Arcane Engineering

The Gorilla of Destiny

September 24, 2024

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Contents
1 Introduction 5 Battery Dump . . . . . . . . . . . . . 26
Legal Information . . . . . . . . . . . . . . 6 Circuit Rules Cheat Sheet . . . . . . . . . . 27
1. General . . . . . . . . . . . . . . . . 27
2 Theory 7 2. Spell Slot Storage . . . . . . . . . . 27
How Spells Move in a Circuit . . . . . . . . 7 3. Resistors . . . . . . . . . . . . . . . 27
Real Circuitry Basics . . . . . . . . . . 7 4. Inductors . . . . . . . . . . . . . . . 27
Kirchhoff’s Laws . . . . . . . . . . . . 8 5. Casters . . . . . . . . . . . . . . . . 27
Arcane Charges . . . . . . . . . . . . . . . . 8 Building Rules Checklist . . . . . . . . 27
Components . . . . . . . . . . . . . . . . . . 10 Chaotic Circuit Failure Table . . . . . . . . 28
Spell Slot Capacitors . . . . . . . . . . 10
Spell Slot Batteries . . . . . . . . . . . . 11 4 The Arcane Engineer Subclass 29
Zeroth Level Batteries . . . . . . . . . . 11 Component Savant . . . . . . . . . . . 29
Resistors . . . . . . . . . . . . . . . . . 12 Component Specialist . . . . . . . . . 29
Series and Parallel Resistors . . . . . . 13 Scavenger . . . . . . . . . . . . . . . . 29
Parallel Resistance Calculation Example 14 Theorist . . . . . . . . . . . . . . . . . 29
Inductors . . . . . . . . . . . . . . . . 15
Logic Gates . . . . . . . . . . . . . . . 16 5 Arcane Engineering Examples 31
Standard Casters . . . . . . . . . . . . 18 Background . . . . . . . . . . . . . . . . . . . 31
Custom Casters . . . . . . . . . . . . . 18 Bait and Blast . . . . . . . . . . . . . . . . . 31
Miscellaneous Components . . . . . . . . . 19 Brief Glimpse . . . . . . . . . . . . . . . . . . 31
Recap of Components and Rules . . . . . . 19 Clown Buzzer . . . . . . . . . . . . . . . . . . 31
Spell Slot Carriers . . . . . . . . . . . 19 Chaos . . . . . . . . . . . . . . . . . . . . . 32
Capacitors . . . . . . . . . . . . . . . . 19 Charming Ring . . . . . . . . . . . . . . . . 32
Batteries . . . . . . . . . . . . . . . . . 19 Crown of Banishment . . . . . . . . . . . . 32
Resistors . . . . . . . . . . . . . . . . . 19 Delayed Dispel Magic . . . . . . . . . . . . 32
Inductors . . . . . . . . . . . . . . . . 19 DO NOT PRESS . . . . . . . . . . . . . . . 32
Logic Gates . . . . . . . . . . . . . . . 20 Firefighter . . . . . . . . . . . . . . . . . . . 33
Casters . . . . . . . . . . . . . . . . . 20 Fire Grenade . . . . . . . . . . . . . . . . . 33
Miscellaneous Components . . . . . . 20 Grease Trap . . . . . . . . . . . . . . . . . . 33
Hand-held Fan . . . . . . . . . . . . . . . . 34
3 Rules 21 Hot Potato . . . . . . . . . . . . . . . . . . 34
Circuit Building . . . . . . . . . . . . . . . . 21 Labyrinth . . . . . . . . . . . . . . . . . . . 34
Number of Circuits . . . . . . . . . . . . 21 Little Big Light . . . . . . . . . . . . . . . . 34
Building Casters . . . . . . . . . . . . . 21 Might Explode . . . . . . . . . . . . . . . . 34
Circuit Damage and Repair . . . . . . . . . 22 Missile Stick . . . . . . . . . . . . . . . . . . 35
Charging Circuits . . . . . . . . . . . . . . . 22 Nuclear Option . . . . . . . . . . . . . . . . 35
Time Delays and Duration . . . . . . . . . . 22 Opus Lux . . . . . . . . . . . . . . . . . . . 36
Detailed Out of Combat Rules . . . . 22 Parachute . . . . . . . . . . . . . . . . . . . 36
Simplified Rules . . . . . . . . . . . . . 23 Passwall Button . . . . . . . . . . . . . . . 36
In Combat Rules . . . . . . . . . . . . 23 Reactive Armour . . . . . . . . . . . . . . . 36
Cost of Components and Component Spell Counter . . . . . . . . . . . . . . . . . 36
Crafting . . . . . . . . . . . . . . . . . 24 The Box . . . . . . . . . . . . . . . . . . . . 37
Spell Casting, Traps, and Learning . . . . . 24 The Scary Orb . . . . . . . . . . . . . . . . 37
Concentration . . . . . . . . . . . . . . 25 The Useless Machine . . . . . . . . . . . . . 37
Counter Casting . . . . . . . . . . . . 25 Vendor . . . . . . . . . . . . . . . . . . . . . 37
Arcane Engineer Spells and Actions . . . . 26 What Was Tha- . . . . . . . . . . . . . . . 38
Repair Circuitry . . . . . . . . . . . . 26
Stabilise . . . . . . . . . . . . . . . . . 26 6 Acknowledgements 39

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Chapter 1: Introduction
Some people have the gall to say wizards can’t
invent things, but with the power of our in-depth
analysis and far superior intellect, we are more than
capable of making enchanted, autonomous, and
arcane systems with nearly twice the organisation
and half the lethality of the other schools of
engineering. This book is split into 5 chapters. First
up is The Introduction, which you’re already
reading, good job. Following that, we have the
real meat of the project, The Theory of Arcane
Circuitry. The Theory will be very technical, and
in this chapter we will explore the implications of
the theoretical choices made, but for the sake of
everyone else at your table, we will then move onto
the third chapter: Rules Implementation. If you
aren’t that excited by the maths, this is the chapter
for you; it contains all the information you’ll need
to actually play the class with rules based off of the
theory. After this, we have the Arcane Engineer
Subclass. This is just a simple combination of some
of the rules into a subclass for you to use in your
own games. Finally, we have Arcane Engineering
Examples. these are some circuits I’ve made up
that I think follow the rules, unless otherwise stated.
This book has become a huge project sort of by
accident. I appreciate everyone’s patience around
its writing, and I hope that it can somehow live
up to your expectations. However, like all my
work, there are likely a myriad of typos, errors,
inconsistencies, contradictions, and mistakes. If
you find any, please just let me know (email is
best: gorillaofdestinytiktok@gmail.com), and I will
attempt to rectify them ASAP.
Finally, I would like to thank George Eracleous
for all the wonderful art in this book as well as
Stenis for the graphic design of the heraldry, page
background, and the circuit diagrams in the Arcane
Engineering Examples. And, of course, I would like
to thank all of you for your continued support. If
you enjoy my work, a rating is much appreciated,
but don’t feel obligated.
Thank you, The Gorilla of Destiny.

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 Legal Information
This work includes material taken from the
System Reference Document 5.1 (“SRD 5.1”)
by Wizards of the Coast LLC and available at
https://dnd.wizards.com/resources/systems-
reference-document. The SRD 5.1 is licensed
under the Creative Commons Attribution
4.0 International License available at
https://creativecommons.org/licenses/by/4.0/legalcode.

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 (get it? if you don’t, keep reading, then come
back and have a good 5 to 10 minutes of laughing
Chapter 2: Theory to yourself before leaving a five-star review) our
development of arcane circuitry. Similar to our
distance calculations, however, much of the theory
One key thing that I have to emphasise a lot we develop as a result of the rules we see will be too
throughout my work is “Magic isn’t real.” Now, frustrating to impliment directly and so we will also
obviously, I’m not talking about the magic of present a simplified version of the rules for play.
hearing a song from your past you had never Finally, at the end of this section, I will try and
forgotten but couldn’t remember, the magic of include a short recap of all the different components.
laughing with your friends so hard your head begins
to hurt, or even the stage shows involving cards
and cups. No, what I mean is that the magic, as How Spells Move in a
described in the rules of 5e, is almost certainly
not true. When we play these games, we must Circuit
accept a certain amount of fantasy and deviation Real Circuitry Basics
from our otherwise sensible universe. This isn’t to
the detriment of fantasy. In fact, one of the main In the earlier stages of whatever physics education
appeals is being able to escape from the boring, and you might have had, you may have been told to
often much more complicated, rules of reality and think of circuits as electrons moving around a
tell stories in strange worlds but with real human circuit, being given a certain amount of energy
truths at their core. When we embark on these (called voltage), which they then deposit at
“scientific” magic projects, we have to “buy into” the various components (resistors, lamps, etc.).
this a little bit. We must remove ourselves from Somehow, these electrons know to spend their
reality and instead think of ourselves as scientists energy exactly so that they return to the battery
in these different and strange worlds, including all with absolutely none left. This isn’t quite right but
their ridiculous rules. We can’t fall back on real- is useful as a starting example. In reality, currents
world understandings and must instead build our flow because of a “push”, and the voltage describes
new science on the fantastical evidence presented to how strong this push is. The “push” comes from
us. Most often, that evidence comes in the form of a the repelling force like charges (charges with the
rule book. same sign) give each other (similar to how magnets
attract if you have opposite poles but repel if you
We are forced to import some understanding from
have the same pole). An electron is moved by some
our reality, such as the fact that c2 = a2 + b2 in
electromotive force (emf), which then causes the
the universe’s geometry despite the rule book saying
next electron to feel a push from their mutual
that the length of the diagonal on a 5x5ft square
repulsion, which will then repulse the following
is 5ft. If we took that at face value, the geometry
electron, and so on, and so forth. When we flip a
of our fantasy world would be so unrecognisable
switch off, we break the loop, which means there
and technically complicated that we would never
is nowhere for pushed electrons to go, stopping the
get anything done and probably leave quite angry.
circuit. The flow of this electric charge is called
Similarly, if we had to specify that we are moving
the current (analogising very well with a current of
7.071...ft every time we moved diagonally, we’d
water), and different components require more or
get frustrated with the game. So, we assume these
less energy to be pushed through. This resistance to
particular rules are just simplifying the reality of
this flow is called (wait for it) the resistance. Ohm’s
our movement for the player’s convenience and not
Law tells us the relationship between these three
as a bold scientific statement that the space-time
properties:
curvature of the fantasy world is so fundamentally
altered that it justifies these distances.
V
Therefore, we have two kinds of evidence: I= (2.1)
R
hard rules that have no real-world allegories
(i.e., spell levels, damage, hit points, etc.) and where Current I is defined by the voltage V and
rules of convenience that we can ignore. Why I resistance R. Components with a higher resistance
even mention this is because we are going to be require more “pushing” from the voltage, and that
building a system for magic circuitry. Much to affects the current of the entire circuit. One of
my undergraduate self’s dismay, circuitry is a real the key takeaways from this is that current is the
thing. The real-world rules of electromagnetism same everywhere in the circuit (provided it doesn’t
are complicated and not entirely useful to the split anywhere, see next section). It is not like a
very discreet world of 5e magic. So, here we are, river with some regions of high speed and some of
obviously taking inspiration from the real-world, low, but instead, the flow is constant due to the
but most importantly, we want to try and keep balancing of the emf given by the battery and the
faithful to the in-universe evidence and not get resistance of the circuit. In Ohm’s law, you can see
distracted trying to make the complicated, nuanced, this quite neatly: if we increase the voltage of our
and fascinating world of real-life circuitry impede battery, then we get an increasing current; if we

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 increase the resistance, we will have a decrease in voltage. This means:
current (and vice versa). ∑
As mentioned earlier, though, the current can V =0 (2.3)
be different in different components of the circuit, ∑ ∑
⇒ Vin = Vout (2.4)
but in order to understand why, we must look at
Kirchhoff’s Laws (Next Chapter). In the real-world, ∑
where Vout is the sum of ∑voltages used in each
the very basic idea of circuitry is this: that there is
component of the circuit and Vin is the sum of
one force pushing the electrons around the circuit
input sources of voltage. So, if we have a single
and another force pushing them back, resulting in a
component (a lamp for example), we use all of our
current that sits in the happy balance between the
voltage in that component. Looking at Ohm’s Law,
two.
we can see that this can result in a dangerous or
I will confess now that circuitry was never my unwanted amount of current in our component. But
chosen subject in university, and while I will if we add a resistor, then we will have some of the
attempt to do it justice, there are thousands of voltage used to push through that resistor which
details I’ve already omitted, but for the sake of reduces the circuit’s overall current. This is why we
arcane engineering, this simple idea will suffice. The have components such as fuses, which will break if
other important fact I will ignore in developing this the current is much higher than is safe.
theory is Alternating Current. With all of this in mind, we are now, finally,
Alternating Current (AC) comes from the able to start thinking about how we might make
movement of electrons back and forth; this is something analogous for the magic in 5e. Keep in
actually the far more interesting side of electricity mind that our main focus is not to recreate these
in the real-world (in my humble opinion), allowing laws and phenomena in 5e but instead use them as
us to build filters for musical instruments, self inspiration as we build around the known evidence
correcting circuits, and many other complex effects. of the rule book. Given their importance, we will
But as we will discuss later, there is no need for any also talk about each individual component’s arcane
understanding other than the simpler Direct Current cousin in their own subsection.
(DC). With that, we can cover the second half of our
brief tour of real circuitry.
Arcane Charges
Unlike real-world voltages and currents, magic is
Kirchhoff’s Laws incredibly discreet1 . There is no fractional spell
These are some simple principles from real circuitry slot2 ; the requirement of the spell is either met or
that I think will prove useful to us in the future it isn’t (or it is upcast, again by a discrete level).
development of the arcane circuitry system. This is A lamp can be brighter when more current flows
where I find the analogy of rivers to be immensely through it, but a fireball will always cost a 3rd level
helpful. The first law is that all current entering spell slot and no less. As such, we differ almost
a junction must be equal to all current leaving a immediately from real circuitry in that our circuit
junction. In terms of our rivers, this makes perfect is not a traditional flow of current as it is in a
sense. If the river splits at a junction, the total standard wire.
amount of water coming out must be equivalent to We choose to say that spell slots are not moved
the total amount of water coming in. Similarly, if by a magic pressure that forces inherently magic
two rivers meet and combine, they will also have the particles in material to flow in a similar way to real-
sum of water in = sum of water out: world electrons (though such a system might be
a workable model for other systems, hells, maybe
∑ ∑ even a follow-up book to this one). Instead, we
I0 = Iout (2.2) imagine our wire being a material that can carry
∑ a small fraction of a spell slot known as “Spell
The symbol simply means ‘the sum of’ and will Slot Charges.” You might be concerned given I
feature a lot in this book. Essentially
∑3 put, we could just mentioned that “there is no fractional spell
write a simple version like n=0 n = 0 + 1 + 2 + 3 = 6. slot,” but I hasten to add that that is in reference
In that example, we have included limits of n, but in to casting; we cannot have half a fireball cast, but
cases where we are dealing with arbitrary amounts there is no reason to believe the energy itself cannot
(like above), then we simply omit these from the be moved in discrete packets that carry a fraction
notation, which suggests “Sum of however many you of the total amount of energy required. There are
have.” two possible methods of modelling these charges,
The second law is that the sum of voltages must either in a way similar to spell points, where they
equal 0 across the circuit. When we add voltage are identical regardless of level, and when enough
using a battery, generator, or some other means, pass to the caster (see Casters section), they will
we consider that a positive voltage. When we lose cast at their given level. Or in the model we will
voltage to components, we consider that a negative go with, the spell slot charges have their level data
1“Discrete” in physics means something is individual, distinct, and not continuous.
2 Technically there are spell points, but these are less commonly seen and even then they’re still discrete.

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within them and cannot mix with other levels in In one action, we want a single spell to be cast; if
the same wire. This leads to some interesting ideas, we say the time for a spell of level L to be cast is TL
such as “Can we filter out different levelled charges with the requirement TL ≤ TA < 6 seconds, we can
and have them travel along the same wire for long define the current I as:
distances then separate them out again?”, while
the other method would not require such filtering. Lmax
I0 = (2.5)
However, the first method would also restrict the TA
ability to up-cast spells by changing the source, and where I0 is the default current without any
instead, you would have to change the caster. resistors in the circuit (discussed in the Resistors
Ultimately, this is irrelevant; there may be section), the units being “spell slot levels per
interesting implications of one system over the other second.” Lmax is the maximum level that can be
that become clear in future research, but as things cast (i.e., in 5e, we have Lmax = 9, but perhaps
stand, it is simplest (and most in line with the most you would want to set it to Lmax = 7; for
commonly used rules) to take spell slot charges at a example, it matters not to the maths). We might
given level spell slot. If you prefer the other system, also have Lmax determined by the material used in
it should be almost trivial to alter the following the circuitry with only the rarest materials being
model to your liking. able to cast 9th level spells; as such, we will just
We will have to assume that this arcane keep Lmax as a variable throughout the theory and
conductive material (or group of materials) exists. use Lmax = 9 for most 5e rules.
Its rarity, name3 , and physical properties are a From this, we can then define the time needed to
decision for the GM as they are mostly unimportant cast a spell by rearanging eq. (2.5):
for our work here where we can just say, “This L
material exists, and we can make wires and arcane TL = (2.6)
I
components from it.” In this material, the “Spell You’ll notice here that if we then cast a spell with
Slot Charges” can carry a finite fraction of any spell L = Lmax , we have TL = (Lmax Lmax
/TA ) = TA as
slot with them; they have no care for what level they 4
expected . More properly, this means that:
are carrying, merely that they are carrying it. They
will carry this fraction of a levelled charge through L
to the final spell casting component, which will do TL = TA (2.7)
Lmax
nothing until a spell slot’s worth of charge has been If we say each carrier takes a fraction of a spell
deposited, at which point it will cast immediately slot f (by default, f = 1000 1
seems reasonable).
(how it knows what spell to cast we will discuss in 1
We will need f Spell Slot Carriers (SSCs) to carry
Casters section). a full spell slot over in TL , that means there are
This might all seem super arbitrary: How many 1
f ×TL SSCs per second passing through a given part
per foot of wire? How fast do they move? What of the wire for a given spell slot level. Again, more
fraction of a spell slot is carried? These are all generally:
fascinating questions that I think you should have
an honest attempt at answering. That said, they 1 1 I
can ultimately be arbitrarily decided. We can decide # of SSCs per Second = = L = (2.8)
f × TL fI f L
their speed and fractional spell slots semi-arbitrarily
so long as they can follow the regular rules of 5e. Though, these factors are not likely to come
Yet even there, we have some further arbitrariness. up in later theory. This is just a very technical
According to the rules, a single round takes 6 exploration for those with the will and strength to
seconds, and in that, you and everyone else get your indulge me in it.
movement, action, bonus action, and potentially, When an SSC has dropped its fraction at the spell
reaction. For balance, it seems like a natural choice casting component, it will then carry on through
to say our spell slot charges move at such a speed the wire until it again reaches the battery or a
and in such a density that in a single turn, they can grounding element. For most batteries, they will
cast one spell in a single action. Throughout, we require a loop such that the battery finds new SSCs
will use TA to notate the time chosen to take for an to charge while possible. My understanding of
action; in many cases, we might choose TA = 1 since this would be that when charged by the battery
that keeps the maths more simple, but ultimately, with a fraction of spell slot’s energy, the SSC will
this decision is arbitrary so long as TA < 6 seconds. move through the wire (perhaps even directed by
If you do want more specific values (maybe you are it), which will stop if the circuit has nowhere for
one of those wonderfully technical players who are it to go (e.g., a switch). In order for the current
planning things beyond even my imagination; if you to stop flowing, there must be some counter to
aren’t that fussed about the technicality and maths, the movement induced by the battery. In real
feel free to skip to the next section), we can simply circuitry, this is our electron’s repulsion. We do
calculate them. not want to limit arcane batteries by saying their
3 Electrum does seem appropriate.
4 Similarly, we are defining here that higher level spell slots take longer to cast. This will be important later, but I choose to
justify it by saying it is because more powerful SSCs require more time to direct and control safely

9
 switches must be immediately after the energising Spell Slot Capacitors
station, and so we must assign some level of mutual
repulsive force to these charges that can overcome
the force to move and hence stop the circuit. The
battery will only be able to charge new SSCs
passing through that are being forced to stop by the
unmoving charges in front of them. One interesting
consequence of this is that if the spells have some
momentum, they will likely keep it, allowing them
to further push into the resistance of unmoving
charges. The consequences of too large a buildup in Figure 2.0.1: Example of an arcane capacitor being
the circuit will be our fail state or circuit building grown and then stacked to form a battery
and will be discussed in Circuit Failure.
Spell Slot Capacitors are the foundation of arcane
This finally gives us the basis understanding. batteries. In the real world, capacitors are not the
Spell Slot Carriers (SSCs) are found in certain rare foundation of batteries but instead two conductive
materials that function as the foundational material plates separated by some distance with some
for our arcane circuitry components. Batteries insulating material between them (such as air). The
(which we will discuss in more detail in Spell Slot insulation prevents charges from moving through the
Batteries) are constantly trying to use stored spell circuit and instead cause, a potential difference to
slot energy to move SSCs that, in an open circuit, build between the two plates. The capacitance of
are resisted by the SSCs’ mutual repulsion. When the resistor is defined using the charge it can hold
the circuit is closed, this force will dissapear and “Q” and the potential difference “V ”:
the charged SSCs will move through the circuit,
pushing any uncharged SSCs along with them back Q
C= (2.9)
to the battery. When these SSCs arrive at a spell V
slot component, they deposit their charge, and once In a DC circuit, the charges will accumulate in
a full spell slot charge is accumulated in the spell one plate, and they will begin to resist the flow of
casting component, a spell is cast. new electrons onto the plate with their own negative
charge, eventually building up enough repulsive
If, for whatever reason, a SSC escapes the circuit force to push against the emf, forcing the current
the energy is let off as bright light and heat (which to stop entirely, which stops the buildup of more
may harm you at a certain level; we will discuss electrons and so an equilibrium is reached. If we
this more in Rules). This is a sharp and sudden then discharge this capacitor, we will quickly release
decay of energy as the spell slot uses itself up in this accumulated store of electrons. There is much
other ways so quickly, we treat it as effectively more fascinating detail about how they interact with
instantaneous. alternating current (AC) circuits and how they allow
us to filter signal frequencies, but that will have to
This is barely analogous to real-world circuitry wait, as we have far more important magic material
at best, and there’s every chance that our attempt to cover.
to form this allegorical system at all will lead to so In our case of arcane capacitors, are levelled
many issues that fundamentally destroy it. I urge spell slot holders. You might like to think of these
the reader to try and find them; consider this not to as small crystals that glow when holding spell
be taken as the written law of a god, which cannot slot energy (rules for how these are charged are
and should not be broken. Instead, see it for what described in Rules). Capacitors are, like spell
it is: A crackpot theory for fictitiously observed slots, levelled. A 1st level capacitor can only hold
phenomena; if you can think of a better method and a 1st level spell slot, a 2nd level capacitor a 2nd
theory, then by all means do so. level spell slot, and so on. Much like real-world
capacitors, these are slow to charge but relatively
fast to discharge. When an uncharged Spell Slot
Carrier (SSC) is input into the capacitor, it is given
some of the spell slot’s energy, which forces it to
Components continue moving in the circuit (and hence moving
the rest of the SSCs in the circuit).
Most capacitors cannot hold a spell slot for an
In this section, we will discuss each of the infinite amount of time. In fact, we can define their
components necessary for basic arcane engineering. capacitance as it tells us how quickly spell energy
At the end, I will give a brief summary since there within them will decay. Capacitors are defined by
is already a lot of heavy theory, which will just two numbers: Primary Capacitance Time “t0 ” and
end up in a simplified form anyway, and I want to Capacitance Decay “C” (this is quite different to
give people the quickest route to playing with these real-world capacitors now, just to be clear). t0 tells
systems. us how long the capacitor will remain stable for,

10
that is for a time of t0 the capacitor will store the In order to make this more convenient to play
spell slot without decay. After t0 , however, the is to simply say a battery will lose all of its charge
spell slot amount stored within the capacitor will be after a long rest (even though it isn’t technically
defined as: a limitation with the maths we have currently).
Similarly, we can simplify things by limiting
S(t) = S0 e−C(t−t0 ) (2.10) batteries to have identical capacitors within them
(i.e., the same values of C and t0 ).
The eagle-eyed amongst you will notice that as
soon as we are past t0 , this is not enough energy to There is much argument within the Wizards of
cast a spell as S0 = 1 (since we have only one spell the School of Arcane Engineering about whether
slot per capacitor), and therefore S(t) < 1 ∀ t > t0 , it is better to charge every capacitor equally or to
which means you cannot cast a full spell5 . In order charge an equal number of capacitors as you are
to solve this problem, arcane engineers will often opt putting spell slots into the system. In reality, it
to string together capacitors into “Arcane Batteries.” doesn’t really matter, which makes the arguments
I would suggest the default value for t0 is 16 hours even more heated.
(i.e., a full day of being awake before a long rest).
One fun legendary item you can offer a player is To recap, this means batteries have three
the idea of a “Zero Capacitance Decay Capacitor” parameters.
(ZCDC, even reading that gives chills of excitement,
doesn’t it?). If C = 0, then no matter how long
it has been since the capacitor has been charged
• N : The number of capacitors
S(t) = S0 ∀t. A 9th level ZCDC is the stuff only
• C: The Capacitance Decay of each capacitor
whispered by maddened wizards.
• t0 : The Primary Capacitance Time for each
capacitor
Spell Slot Batteries
These are simply a clustering of Spell Slot As an Arcane Engineer, you are much more likely
Capacitors to try and overcome pesky things like to encounter batteries than capacitors in your day
only being able to cast once and not being able to to day, so for my sake, your fellow player’s sake, and
hold a spell slot over a 24-hour period. If we have your GM’s sake...just use the simple version6 .
two capacitors placed in our circuit one after the
other, when empty charges pass through the empty
capacitor, they will continue to the next; if that has
energy, they will be able to pick it up from there. Zeroth Level Batteries
Therefore, two half charge capacitors are as good
as one fully charged capacitor capable of casting If you have read some of my previous work, you’ll
a single spell. If we have a standardised battery know I have this irritating habit of calling cantrips
where every component capacitor has equal C and t0 “zeroth level spells.” This will be no different, and
values, then we can write the total number of spell you will never stop me. A zeroth level battery is
slots as a sum of their individual values. Before t0 quite simple; it draws on the natural magic energy
(assuming all capacitors are charged), we can simply in the world around us and passes zeroth level spell
say S = 1 + 1 + 1 + ... = N for an N capacitor battery. charges through the circuit. These can be used for
However, after t0 : casting as well as basic logic within circuits without
using your own charged spell slot energy. Typically,
∑
N
the current of a zeroth level spell slot can simply
S= e−C(t−t0 ) = N e−X(t−t0 ) (2.11)
i=0
be output into the air without causing much more
than a spark as the Spell Slot Carriers dissipate and
where, we horrible people, we could make this eventually lose their withheld energy; to account for
incredibly complicated by considering the case where this, these batteries are not filled with capacitors
we charge each capacitor at a separate time “ti .” (as they draw the energy required as needed) and
At which point, we would have to consider each instead SSC rich materials such that even with the
of the batteries capacitors separately for whether excess being dissipated into the air or ground, they
they are 1 or have begun to decay and then sum the will not run out. That said, most of this “grounding”
values of these decays. If you want to keep track of effect is kept for logic gates, which we will discuss
that, be my guest, and it will be more technically in Logic Gates, as the alternative will be to allow
correct. Similarly, we might have capacitors each your zeroth level battery to continuously charge
with different values of C and t0 , which would make and run out of its reserves of SSCs much faster
our equation the terrifying: than anticipated and hence become useless. Most
arcane engineers only need to swap their zeroth
∑
N
S= S0,i e−Ci (ti −t0,i ) (2.12) level batteries out once every few years; most carry
i=0
enough replacements to last their lifetime.
5∀ is just a fancy maths way of writing “for all.”
6 Please.

11
 Resistors L LR
TL = I0
= (2.16)
R
I0
Then, from eq. (2.14), we can substitute I0 :
1
TL = (LRTA ) (2.17)
Lmax
We call this equation The Resistor Equation
as it tells us the time it will take to cast a spell
of level L given our chosen TA and the resistor R.
This leads to the first obvious question: What is
the maximum resistance we can add to any given
circuit? Well, we can set a simple restriction that
TL ≤ TA . hence:
Figure 2.0.2: Example of an arcane Resistor
TL ≤ TA
Resistors are fairly simple in their effect; they 1
(LRTA ) ≤ TA
change the current of the circuit. In the real-world, Lmax
this can be done by using a less conductive material LR
(i.e., more force is required to push electrons through TA ≤ TA (2.18)
Lmax
the resistor and hence more energy is used), to make LR
the material thinner, which reduces the amount ≤1
Lmax
of electrons which can pass through at a given
Lmax
moment, or making the material longer, which R≤
L
means electrons have further to push in order to
pass the current through. Note here, we are using TA , as some spells require
In our wonderful world of arcane engineering, we bonus actions to cast. You may wonder if that has
only use the first option, special materials that do any bearing on the spell as TA will become TBA .
allow for our spell slot charge carriers to pass but The answer is not simple, as bonus action spells still
at a much slower (or potentially faster) pace. While require an entire spell slot and this systems works
charges will enter the resistor at the normal pace, by slowing the number of spell slot charges; thus we
they will backup as they are slowly allowed through assume that the bonus action/action divide is not
the resistor (the dangers of this will be discussed one of time and one of personal energy or mental
shortly). In Arcane Charges, we described the capacity. Thus, we have, for all action and bonus
time taken to cast a spell of level L as: action spells, the Resistor Limit Equation:

L Lmax
TL = (2.13) R≤ (2.19)
I L
with I being the current of our Spell Slot Carriers. In simple terms, this means that the maximum
The default current is defined as: resistor allowed for a given circuit relates to the
spell level you intend to put through a circuit. If
Lmax you will only cast spells of level 1 through, then
I0 = (2.14) R ≤ 91 ⇒ R ≤ 9; if I will pass levels 1
TA
through 3 through my circuit then the maximum
where TA is the time we choose an action to take safe resistance is R ≤ 39 ⇒ R ≤ 3. If your
(e.g. TA = 1s) and Lmax is our maximum level we resistance exceeds this inequality, then the Spell Slot
can feasibly cast (typically Lmax = 9). This is Carriers building up in your circuit will become too
chosen since we expect a Lmax level spell to still dense with energy and cause a chaotic explosion or
be cast within an action (provided it isn’t a ritual release of magic (see Circuit Failure). A buildup
spell). of level 9 spell slots is significantly more dangerous
The new current after we add a resistor of than level 1, and so it follows that lower level spells
resistance R to our circuit is: can withstand buildups more effectively. Specific
implementations are discussed in the Rules chapter,
I0
I= (2.15) but in a pure theory sense, I imagine it similar to
R wild magic or a powerful raw explosion of that spell
This equation provides us with our definition of level. This could be cleverly used if someone were
resistors. Our resistors slow down the current by a devious enough (and brave enough) to try.
factor of R, and thus, the resistance of a material What if R ≤ 1? The Spell Slot Carriers accelerate
tells us by how much the spell slot carriers are again. Since most spells cast are instantaneous, this
slowed. Using eq. (2.13), we can substitute our new does not usually matter, and spells that take longer
value for I: to cast such as ritual spells cannot be performed

12
by circuits (as of yet, perhaps new research will
allow for such things). One potential use is that if
we slow our circuit down for some reason (perhaps
before a split in wire), we can use a resistor with a
resistance of 2; we could then return the current to
normal frequency with a “resistor” or resistance 0.5.
This provides an interesting idea of how we return Figure 2.0.3: Two examples of how resistors may be
charge carriers to the battery. At the moment, set up. On the left, we have resistors in series, and
the best practice seems to be that the battery has on the right, we have resistors in parallel.
them in such abundance that it does not matter
the rate of return as the reserve is always vastly We can calculate the total resistance of N resistors
higher. This makes life simple. However, we could in series as:
always add a restriction of resistors such that they
are in fact “brackets” of sorts in our circuit, that for ∑
N

every resistor with resistance R, there must be an RT = Ri (2.20)

equal and opposite resistor that has resistance R1 . i=0

In such a scheme, the current will always return to which is just a fancy way of saying, “We add them
1, and the battery will have no net-loss of spell slot all up.” So in Figure 2.0.3, we have two resistors
charge carriers. But I personally think that will over- with resistance R1 and R2 , respectively, their total
complicate things too much for effectively the same resistance RT will be RT = R1 + R2 . In parallel,
result. things get slightly more complicated. We instead
The primary use of resistors within arcane calculate the total resistance of N parallel resistors
circuitry is to delay casting and time combinations using:
of spells. For example, in the following diagram,
you can see that we have two circuits that can be 1 ∑ 1 N

combined (as we’ll see later) to begin at the same = (2.21)

RT i=0
Ri
time. Using Equation (2.17), the first will cast spells
with TL = 91 (1 × 1 × TA ) = 91 TA while the second will If there are series resistors within the parallel
cast within TL = 91 (3 × 2 × TA ) = 96 TA (i.e., 6 times parts of the circuit, then we can add them up
as long as the first). and treat them as a new resistor in our future
calculations.
However, in arcane engineering, we deviate in
some interesting ways due to our original choices
of how Spell Slot Carriers are carried around the
circuit (which tempts me even more to make a
follow-up book for this exploring a more real-life
similar model). Equation (2.15) tells us that I =
I0
R . If we imagine two resistors in series, the current
going into the first will be I0 , and the current
coming out will be I1 = RI01 , which will also be the
current going into the second resistors. The current
coming out of the second resistor will be:
0 I
I1 I0
I2 = = R1 =
R2 R2 R1 R2
Or, more generally, for N resistors in series in
an arcane circuit, the new resistance becomes the
equivalent of a single resistor with total resistance
RT given by:

RT = Π N
i=0 Ri (2.22)
If you haven’t seen ΠN before, it is the
Series and Parallel Resistors i=0 ∑
multiplication equivalent of , so Π3n=0 n = 0 ×
What if there is more than one resistor in the 1 × 2 × 3 = 0. The total resistance must still follow
circuit? In real circuitry, we have two cases that will the rules of Equation (2.19), so be warned those who
help inform us what to do with arcane engineering, add too many resistors in series. The main use of
and these are called “Series” and “Parallel.” When this is to effectively create a new resistor with those
resistors are in series they are happening one after which you already have.
the other along the same wire. In parallel, they are If our resistors are in parallel, it is much more
happening along different paths of different wires similar to the real-world case, but the interesting
after a junction: part for us is not the overall reduction in current but

13
 how much goes to which parts of the junction. As And so, we pass the second requirement. In the
we know from Kirchhoff’s Laws, the∑current∑must example above, we can use eq. (2.23) to determine
split at a given junction such that I0 = Iout . In that the current passing through the lower branch
the branch with the least resistance, we expect the (I2 ) and the higher branch (I1 ) will be:
most current to flow. The current in a given branch
‘n’ of parallel resistors (In ) is defined as:
1
In = ∑R n
I
N 1 0
(2.23)
i Ri

∑where
N 1
Rn is the resistance on branch n and
i Ri is the summation of 1 over each branch’s
resistance and I0 is the current (after having been
slowed by these resistors). The brilliant amongst
you will notice our denominator looks suspiciously
like eq. (2.21), and we can then say that the total 1
1 2
resistance follows the same equation in arcane I1 = 1
1
1 I0 = 3 I0 = I0
engineering and real-life. Thus, we have two 1 + 2 2
3
1 1
(2.25)
restrictions to follow in parallel casting: 2 2 1
I2 = 1 1 I0 = 3 I0 = I0
1 + 2 2
3
1. The resistance in individual branches must follow
R ≤ Lmax
L

1
∑N 1
2. The the total resistance given by RT = i Ri
must also follow RT ≤ Lmax
L

Parallel Resistance Calculation

Example
Consider the following example:

We can then confirm that indeed after casting, the

current will sum to I0 as expected from Kirchhoff’s
Laws. We can also see then that the current through
the first branch is twice that of the second and thus
will cast twice in the time it takes to cast one spell
in the lower branch. This is how we can time spells
to a great degree of detail within our contraptions.

With that, we have finally detailed how resistors

work in Arcane Engineering. These are fairly
detailed rules and implementations we will attempt
to simplify in Rules, but I want to highlight
that these are in fact very difficult, and if you
If we have level 1 spells, for example, then we didn’t quite understand it in parts or whole, that’s
have satisfied requirement one as both individual perfectly understandable. Despite having gotten
resistors are below R = 9. The overall resistance RT A’s in courses directly about this exact subject, I
is given by: still needed a lot of pen and paper to get my head
around parts, so if you are also finding it a bit much,
that’s an entirely reasonable response.
1 ∑ 12
=
RT i=1
Ri
1 1 1
= +
RT R1 R2 One of the most interesting things about parallel
1 1 1 (2.24) resistance (in arcane engineering) is how unnecessary
= + it often is; it might allow for some of the real clever
RT 1 2
1 3 clogs to do some truly ingenious things, but for
= most purposes of timing and casting, I found two
RT 2
2 separate circuits performed just as well while also
RT = being easier to verify they were valid by the rules.
3

14
Inductors magnetic flux ΦB produces a voltage:
dΦB
V = (2.26)
dt
where flux is just the physics way of saying “How
much of this field is passing through a given area.”
The term dΦ dt simply means “The change in the
B

magnetic flux with respect to time.” This may all

seem overly complex, but I assure you that these
formal and nuanced equations and definitions can
help us reveal the strange perplexity of our universe,
but for our purposes we will keep it relatively
simplified in necessary understanding.
Because of this negative voltage (from eq. (2.26)),
the inductor actually works against the forces
pushing the electrons in the battery and thus resists
the change in current. How much this inductor
resists the change is defined by its inductance: L =
ΦB
I . Rearranging this a little and plugging into
eq. (2.26), we get:
d dI
V = (LI) = −L (2.27)
dt dt
where we are able to move L out of the derivative
d
Figure 2.0.4: Example of an arcane Inductor dt since it doesn’t change with time. If you
remember from earlier definitions, V being negative
This is the last major component we will talk about shows that it is going against the emf of the battery,
but certainly one of the more important. In the resulting in a direct relationship between the voltage
real-world, inductors rely on the fundamental resisting and the change in current. However, since
relationship between electricity and magnetism. this induced voltage slows down, the change in
Every time an electric charge moves, it generates current over time dI dt also reduces, which reduces
a magnetic field in a circular arc around itself. the magnetic flux and then the voltage, which
This behaviour is very accurately modeled by most reduces the resistance to the current such that it can
right hands. If you form a thumbs-up sign with increase again (but slower than before). Eventually,
your thumb pointing straight up and your fingers the current will reach a steady value and with no
closed into a fist, you can think of your thumb as more change in the current V = −L × 0 =
representing the direction of current (which is, by 0. At this stage, there is a steady magnetic field
a frustrating convention, the direction of positive running through and around the coils of the wire
charge flow and hence the opposite of electron and no more opposing voltage. This works in the
flow direction), and your fingers will represent the reverse as well now, and if the current shuts off
circular magnetic field these moving charges have and begins to reduce, then the inductor will form a
created. This rule is, of course, reciprocal as well, as positive voltage and oppose that change as well by
a moving magnetic field can generate electric current generating a voltage as current decreases.
(an incredibly helpful fact for electricity generation). One of the really cool things we can do with this
These laws were codified with Maxwell’s Laws of is transfer energy from one inductor to another.
electromagnetism and while they are incredibly As we (well, Maxwell) discussed earlier, electricity
fascinating, I might have to leave their exploration and magnetism are intrinsically combined, and so
for another time. The key is: Electricity and placing another inductor near one with a steady
magnetism are intrinsically linked. This leads to magnetic field can induce a current in the other
all sorts of fun physics, such as the speed of light inductor, allowing the transfer of electric energy
(Electromagnetic Radiation), energy generation, and through the magnetic fields! We call these systems
modern electrical instruments. “transformers”, and the exact voltage transferred is
In an inductor, we coil wire together such that our defined as:
electrons move in a circular motion, and this creates √
a magnetic field. When we first pass a current L2
V2 = k V1 (2.28)
through our inductor, the change in current causes L1
the magnetic field to similarly change, which itself Like so many things in physics, I have ignored the
causes a voltage (or electromotive force) to push three or so pages of derivation to get to this result,
against the flowing electrons. Specifically, according but I am personally a big fan of complex derivations
to Faraday’s Law of Induction7 , the change in that result, in outstandingly simple equations. The
7While it isn’t always good practice to cite Wikipedia, I can highly recommend googling terms like these if you are more

curious, and often for physics, the Wikipedia page is reliable. If in doubt, you can check the sources.

15
 value of k is the coefficient of coupling between the This scheme means we could effectively transform
coils, but for our sake, we will say k=1 (i.e., we did a level 4 spell slot into a level 2 spell slot using a
it perfectly, also known as an “Ideal transformer”). level 4 and level 2 inductor in seperated circuits.
N2 2 This maths definition can be rewritten slightly to
We can even reduce this further since L L1 ≈ N1 , so
2

we can rewrite eq. (2.28) in terms of N1 and N2 (the show that:

L2 L2
number of loops in each inductor): = (2.32)
L1 L1
N2 which means our transformer rule can simply be
V2 = V1 (2.29)
N1 put as transforming from circuit 1 to circuit 2. You
simply use the inductors at the level in which you
which I think is just very tidy. intend to use in the second circuit to transform from
So what’s the point of my long rant? How can we the level in the first using an inductor of the same
adapt this into arcane engineering using the theories level.
we’ve already built? Inductors in the real-world This is how we might up or down-cast spells.
heavily rely on this electromagnetic connection that I have some debate about whether it should be
we simply do not have in magic. Instead, I posit allowed to up-cast spell slots and it seems for
something somewhat analogous: The moving spell balance’s sake, we must limit this to only downgrade
charge causes a small ripple in the arcane field- spell slots. Or more plainly:
space (commonly known as the weave, though I have
some theories that these may be separate concepts L2 ≤ L1 ⇒ L 2 ≤ L 1 (2.33)
entirely), which permeates all reality and is utilised
by spell casters and arcane circuitry alike. Similar The circuit notation for a transformer is two
to the real-world, if we coil our arcane wires, we see parallel inductors with parallel lines between them
this perturbation in the magic field build up over (since we assume they are ideal):
time, initially resistant due to the tension inherent
to the field (as discussed in the Theory of Magic)
but gradually becoming easier as a more stable field
grows. This field will then, once stability is reached,
resist changes in the circuits state and allow a spell
(that is receptive to such things) to maintain itself
for a given time unless the circuit itself undergoes
enough trauma to rupture the stability of this With that, we now have our large and major
field. The inductance here will then refer to how components at hand. Now we may look at the
resilient the inductor is and what level of spell it can components that really truly unlock the creativity
effectively use. inherent to arcane engineering.
Or in less condescending language: circuit
concentration. For the sake of balance, we restrict Logic Gates
inductors to only be able to function with spell slot
levels at or below their inductance.
The presence of an inductor will allow the casting
of concentration spells through circuits. I must
admit, I find this justification a little too hand
wavey, but it is an important aspect of spells, and
I do think the idea works. In universe, feel free to
consider this a developing theory from an eccentric
academic wizard. In reality, you can call it what it
is: A simple justification for a necessary component
of spellcasting by a person who takes ttrpgs slightly
too seriously.
The second important aspect of capacitors though
is their transformer capabilities. Here, I propose a
very simple relationship to govern the effectiveness
of two inductors:

L2 = ϵL1 (2.30) Figure 2.0.5: Example of arcane Logic gates.

where L1 is the spell slot level input to the
transformer and L2 is the spell slot level after Luckily for us, the similarities between the arcane
transformation. ϵ is the transformer constant defined and real Logic gates will be immense. There will be
by the inductance of the two inductors: some differences later on, but for now, we will focus
on the broad strokes.
L2 Logic gates take one or more binary inputs. These
ϵ= (2.31) are inputs that are either on (1) or off (0) and
L1

16
output a single binary output. These can form Input A Input B Output
incredibly complex digital circuits, but they are 0 0 0
also exceptionally useful for forming more nuanced 0 1 1
arcane circuits. Here, I will cover the simplest Logic 1 0 1
gates and cover their “logic tables” before including 1 1 0
some extra considerations for arcane circuitry.
There are two gates that take in a single input,
the buffer, and the NOT. The buffer gate simply
returns the input while the NOT gate returns the So, what do we need to add to make this
opposite of the input. To show how gates operate, compatible with arcane engineering? Well, it is quite
we can use something called a “logic table” that simple. When using logic gates, at least one of the
gives us all the necessary information for how these inputs to any gates must be connected to 0th level
systems will operate. They have two broad columns: batteries, and by convention, if a non-0th level Spell
input and output. The output column shows us Slot Carrier is passing through, it will be to the B
whether the output will be 0 or 1 for a given output. input, which will then be allowed to pass through
The input columns show us the value for each the output. The unused 0th level Spell Slot Carriers
input node, and we permutate through all possible will be flushed from the logic gate, producing a
combinations of inputs. defuse but harmless magic effect8 . This is a minor
The logic table and symbol for the buffer is: but crucial change as a dangerously under-qualified
Input A Output arcane engineer might accidentally connect his non-
0 0 0 SSCs to the A input and cause a (slightly directed)
1 1 blast of uncontrolled magic energy, and who would
ever want to do that?
These are simple but incredibly powerful systems.
Some gates (such as NOT) will have a circle on For example, if we look at the arcane circuit in
the right hand side of their regular symbol, and this Chapter 2 we can use logic gates to combine the two
means we invert the normal output. The NOT gate circuits to a single switch:
is the inversion of the buffer gate:
Input A Output
0 1
1 0

To justify this in our system we will say the

not gate can only take 0th level inputs and acts
essentially as a 0th level battery. If it receives a
signal it ejects the input, if it does not receive a
signal it sends 0th level SSCs.
For more complex gates, we typically have two
inputs, A and B. For example, the AND gate checks
if both inputs are on, and if they are, then it returns
1; otherwise, it returns 0.
Input A Input B Output
0 0 0
0 1 0
1 0 0
1 1 1

which we can also invert to NAND, which will

simply turn a 1 in the output column into 0 and 0
to 1 (i.e., it will remain on unless both gates are on).
Finally, we also have the OR and the XOR gates:
Input A Input B Output When the switch is closed, the 0th level Spell Slot
0 0 0 Carriers will pass to the two AND gates, allowing
0 1 1 the first and third level spell carriers to pass through
1 0 1 the circuit as intended. This is a very basic example,
1 1 1 but hopefully it is now explaining some of the
complexities.
8Any effect from Prestidigitation seems reasonable

17
 Standard Casters • Conjuration: Yellow
• Necromancy: Green
• Evocation: Maroon

• Abjuration: Indigo

• Transmutation: Orange
• Divination: Cyan

• Enchantment: Pink

• Illusion: Purple

There are, of course, different conventions as

some arcane engineers prefer to personalise their
casters to the spell. Some carve the spell rune
into the stone itself, others choose meaningful
materials to them, and some even use non-
conventional or misleading materials as a trap for
those unsuspecting.
The point is: you can do it however you like, but I
will judge you for not using the same convention as
me (just like real science).

Custom Casters
These are marginally more complicated than the
standard casters but not by much. Instead of
presenting the stone with the inner workings of a
Figure 2.0.6: An example of an Arcane Caster in a known spell, you may opt to instead create your
protective casing own. As you become a more capable wizard, you
will learn new ways of modifying custom casters to
Throughout this entire book, I have been include new components. The different attributes
desperately avoiding talking about what is actually you may customise are the:
casting the magic. That time is over, and now we
must finally discuss the spell casting component. • Spell Level
There are two types: those which cast predefined • Area Type
spells (which we will discuss in this section) and • Damage Type
those which cast customised damage spells (the next • Range
section).
Standardised spell casters are small arcane focuses As these spells are home-crafted, they are not
(such as crystals) through which you have spent a classified into schools of magic (unless the creator
considerable time (approximately one hour for each insists). These spells are generally weaker than
level of the spell) encoding your understanding of the well researched standards but can form useful
the spell through such that they can cast it without custom outcomes. Once created, these can be
direct guidance. This encoding requires your own disassembled and remade.
detailed understanding of a spell and thus is limited
to spells known to the caster. Similarly, this in-
depth understanding of a spell means that arcane Spell Level
engineering is limited to wizards. These focuses will
“remember” these spells until they are destroyed or This is fairly simple: you can select a level up to and
decoded (which takes an equivalent amount of time including your highest level spell slot.
as to encode) and will cast the spell given to them
every time they receive enough power; this is either
through the arcane circuitry as discussed or through Damage Type
the caster themselves (though that seems unlikely A simple selection of either Acid, Bludgeoning, Cold,
as the caster could simply cast the spell themselves). Fire, Force, Lightning, Necrotic, Poison, Psychic,
In circuits, we notate these using a diamond shape Radiant, Slashing, or Thunder damage.
(to represent the common choice of crystal material
by arcane engineers who regularly choose coloured
crystals that follow a convention of colour to school
of magic). This isn’t necessary, of course, and is just
Area Type
convention, and modern magical research suggests Each level of spell can have a single target or an
the schools of magic are themselves arbitrary. Still, area of effect no greater than the values presented in
the convention is: the table below:

18
 Level
0
Cylinder
(5, 10)
Cone
5
Cube
5
Line
15
Sphere
5
Recap of Components and
1
2
(10, 20)
(10, 20)
15
20
15
15
30
30
10
10
Rules
3 (20 30) 20 20 60 20 Spell Slot Carriers
4 (20 30) 30 20 60 20 Spell Slot Carriers (SSCs) can hold a finite fraction
5 (20 30) 30 20 60 20 of a spell slot’s energy and are found in magically
6 (30 40) 60 30 90 30 potent materials such as crystals. They are able to
7 (30 40) 60 30 90 30 pass through certain magic conductors like electrum
8 (30, 40) 60 30 90 30 and have a slight repulsive force to each other, such
9 (40 60) 60 60 120 40 that if the circuit is closed, they will stop moving.
When given a finite fraction of a spell slot’s energy
Table 2.1: Area Types allowed in custom casters for by a capacitor, they will begin to move if they can.
each given level. Cylinder values are given in form When they reach a caster, they deposite this small
(radius, height), Sphere values represent the radius, fraction to a the caster’s larger reserve.
and all values are in units of feet.
Capacitors
Capacitors can hold a single spell slot in them.
Range When SSCs pass through them, they give them
a fraction of that spell slot to carry forwards.
The range is similarly defined as being one of the
Capacitors lose their charge after a long rest (see
following options:
above for details) and must be recharged after.

Batteries
Level Range
Capacitors can be stacked together to form batteries
0 Touch/Self/<60ft
that hold multiple spell slots of the same level. The
1 Touch/Self/<60ft
battery’s level reflects what spell slot it can hold.
2 Touch/Self/<60ft
3 Touch/Self/<90ft Resistors
4 Touch/Self/<90ft
5 Touch/Self/<90ft Resistors slow current down according to their
6 Touch/Self/<120ft resistance: I = IR0 which results in the time
7 Touch/Self/<120ft to cast a levelled spell being defined as: TL =
Lmax (LRTA ) with Lmax being the maxmium spell
1
8 Touch/Self/<120ft
9 Touch/Self/<150ft level and TA begin an arbitrary time taken for an
action. Their primary function is to allow for the
timing of seperate spells in the same combination of
circuits
Predicted Damage Table The total resistance along any given path must
The predicted damage per damage type from the satisfy the inequality: R ≤ Lmax
L .
Theory of Magic given in the tables at the top of the Series resistors can have their total resistance
next page. calculated by multiplying them, and parallel
resistors can be calculated as one over the sum of
one over each individual resistor.
Miscellaneous Components Inductors
I feel it worth mentioning that in your circuits you Inductors allow for spell concentration and down-
may wish to include something that hasn’t been casting. Their level determines the level of spell they
added here. I think, provided they do not produce can use to concentrate with, and to downcast from
a magic effect, that should be fine. For example, two levels, you simply place two inductors of those
a button for closing the circuit, levers, lights, etc. levels near each other (i.e., to go from level 9 to 3
You may also invent components like “magic field you would have two inductors of levels 9 and 3 near
detector,” which could be used to detect incoming each other, though such a waste of a 9th level spell
magic effects. These are up to the discretion of your should be discouraged).
GM, but I believe that they could serve a crucial
and fun aspect to creating your own circuits.
Another interesting idea is transmitter and
receiver components that may allow you to, for
example, use a receiver to trace the strength of a
signal from another circuit’s transmitter, giving you
a rough estimate of its direction, which gets stronger
as you approach.

19
 Level Radiant Poison Piercing Fire Slashing Cold
0 1d8 1d8 1d8 1d8 1d8 1d8
1 1d10 1d12 1d8 1d8 1d8 1d12
2 2d8 2d10 2d6 2d8 2d8 2d10
3 3d8 3d8 2d10 2d12 4d6 3d8
4 4d6 4d8 3d8 3d10 5d6 4d8
5 5d6 6d6 4d8 6d6 7d6 5d8
6 5d8 7d6 5d8 7d6 8d6 7d6
7 7d6 8d6 6d8 8d6 10d6 9d6
8 8d6 7d8 9d6 10d6 11d6 10d6
9 7d8 8d8 6d10 11d6 13d6 11d6

Level Force Psychic Thunder Acid Necrotic Bludgeoning Lightning

0 1d8 1d8 1d10 1d8 1d8 1d6 1d10
1 1d12 2d6 2d8 2d6 1d10 1d10 2d8
2 2d10 2d10 3d6 2d10 2d8 2d8 3d6
3 3d10 3d8 3d8 4d6 3d8 3d8 3d10
4 6d6 5d6 4d8 4d8 4d8 5d6 4d8
5 7d6 6d6 6d6 5d8 5d8 6d6 5d8
6 6d8 5d8 5d8 7d6 6d8 7d6 6d8
7 6d10 7d6 6d8 9d6 7d8 8d6 9d6
8 8d8 9d6 8d6 10d6 8d8 7d8 10d6
9 9d8 7d8 7d8 11d6 9d8 8d8 8d8

Logic Gates
Logic Gates behave very similarly to real logic gates
taking in a number of inputs and a single output.
One of the inputs will continue through the gate
while the other will be ejected. It is vital that
arcane engineers have the ejected input be a level 0
battery as otherwise it can be dangerous (see later).

Casters
Casters have a spell assigned to them by the
circuit designer and will cast a spell as soon as
enough energy has been given to them. You can
use predetermined spells and (if necessary) preset
the choices for casting as well as building your own
caster with equipment that scale with your own
expertise.

Miscellaneous Components
Your GM should allow you to have some level of
custom components within reason. Though, if you
are abusing this, they have my full permission to
have the component break and never ever reappear
again.

20
 Circuit Building
Chapter 3: Rules Circuit building takes time, tools, components,
and expertise. Without considering other abilities,
adding or removing a single component to a circuit
There are a few guiding principles with this rules takes half an hour on top of the base time required
section that I should outline. The main reason for to build a circuit of that size. Only an Arcane
doing so is so that you can modify and implement Engineer may build circuits.
these rules to fit the spirit of the rules if the actual You may wish to have your circuit on an object,
implementation here does not balance well in your which is, of course, fine. There will be some
game. As ever, we should consider the golden rule restrictions, though. You cannot modify the
of ttrpgs: “The GM has ultimate power, and they underlying object on which there is an existing
can remove/modify/add any rule they choose at any circuit without breaking the circuitry itself, and so
time provided such changes enhance the gameplay you must disassemble the circuit before modifying.
experience for the players.” This can be a difficult There are also considerations about the size of the
line to walk; I know I struggle between “Is this underlying object.
monster winning because it’s balanced or am I just
Each component is approximately 1cm (4/10ths
salty because they delayed the session three times in
of an inch) in length, and a quarter of that in width
a row?” So, with the golden rule in mind, here is the
and height. Creating circuits on larger objects
spirit of my rules.
makes them sturdier and capable of holding more
components, but will take more time accourding to:
1. Arcane Engineers should feel 1 like playing a
wizard subclass. It is specifically designed with
the level of technical and specialised knowledge Size # of HP Construction
that defines wizards, and an arcane engineer Components Time
should feel like a specialised wizard. (hours)
Tiny 5 2 0.5
2. The rules should not be restricted by the theory Small 10 5 1
if the theory is inhibiting fun. This was partially Medium 20 9 4
discussed in Spell Slot Batteries where we Large 40 13 16
talked about the simple and complex rules Huge 80 3 HP per 64
implementations (e.g. batteries). While one may component
be more technically accurate if that isn’t fun for Gargantuan 160+ 3 HP per 256
you or your table (and I imagine it isn’t), then we component
shouldn’t be restricted by it.
Table 3.1: Table showing the different construction
3. Circuit construction rules should be simple in rules and properties of circuits with different sizes.
a way a non-expert can understand. Here, non-
expert means someone who hasn’t read this book
(which makes you an expert, congrats). There is
a strong chance that if you use this as a GM or a Number of Circuits
player, you will be doing so with people who don’t Arcane circuits interfere with each other when
share your enthusiasm for this sort of thing. In charged. The maximum number of charged circuits
order to keep things clear, fair, and fun, we should anyone can have on their person at any given time is
do our best to give clear instructions that a non- equal to the intelligence modifier of their creator as
expert can check. you find more ingenious ways to insulate the circuits
from each other. If there are two arcane engineers
4. The Arcane Engineer should not make other then the maximum number is equal to the largest
wizard classes obsolete and should have flaws intelligence modifier but they do not stack.
and failings, things they cannot do that another
wizard might.
Building Casters
With all that said and done...let’s have a go. This In order to have a caster that can cast a specific
section will mostly be discussing the rules we are spell, you must spend one hour concentrating on
implementing and why they have been chosen and the caster to imbue it with the understanding you
how they relate to the theory. At the end, we will have of the spell. Some arcane engineers do this
make a cheat sheet for GMs and players which by carving onto the crystal directly, and others
should include all necessary rules for playing an will write runes around it, others will simply sit in
arcane engineer. If I do my job right, it should cover silence. Once a caster has been set to a specific spell,
a simple A4 page, but knowing me, it will be at least it will take one hour to remove it such that it can be
two. reused.
1Already starting strong with vague language

21
 Circuit Damage and Repair d12
1
Damage Type
Acid
2 Bludgeoning
Of course, your circuits may incur some damage 3 Cold
during your adventures. The circuit has a AC of 4 Fire
10, and when the circuit takes damage its creator 5 Force
must roll an intelligence saving throw to test 6 Lightning
the robustness of the creation. On a successful 7 Necrotic
saving throw the circuit takes no damage, on a 8 Poison
failure it takes full damage. A Variant rule to this 9 Psychic
might be that the AC is determined by size (Tiny: 10 Radiant
19, Small: 16, Medium: 13, Large: 10, Huge: 7, 11 Slashing
Gargantuan: 4), use whichever suits your table best. 12 Thunder
The total hit points of your circuit decided by its
Table 3.2: Damage Type table for a battery dump
size (table 3.1). If the circuit falls below 0HP, it
attack.
will cease functioning, and if its HP falls to negative
values below or equal to its maximum HP, then the
circuit cannot be repaired.
Anyone/anything can activate and use an arcane
To repair circuitry, you must have the arcane circuit, but only an Arcane Engineer can charge
engineer subclass and half the material cost required them since it requires technical knowledge of the
to create the circuit. It takes one quarter of an components to do so safely.
hour to repair each component. Circuits are not
creatures and cannot be healed by healing magic,
health potions, or other medical checks. Similarly,
the mending spell cannot be used to repair arcane
Time Delays and Duration
components as the spell cannot restore magic to an Detailed Out of Combat Rules
object.
Time delays are crucial for so many of the brilliant
(and terrible) contraptions an Arcane Engineer
might dream up. The main issue with this in 5e
is that time falls into two, distinct states: Non-
combat and combat. We’ll begin with the simpler
non-combat implementation.
Charging Circuits As discussed previously, the time to cast a spell of
a given level “L” is given by eq. (2.17) which is:
Charging a battery requires a full turn per spell slot.
This is so that out of combat you can effectively 1
TL = (LRTA ) (3.1)
allocate charges as you please; it makes sense within Lmax
the theory and allows you to cast spell slots through
a circuit if the battery has run dry but you still have
some spare. To maintain balance, we require that Where Lmax is the maximum castable spell level
doing so takes your entire turn (movement, action, (9 in our case2 , R is the total resistance before the
bonus action, and reaction) to do so. As a rule of caster, and TA is the time it takes to take an action.
thumb, the battery will lose all charge after a long Since TA is somewhat arbitrary, we leave it in the
rest but there are magic items that do not have equation as a reference time that can be tweaked by
this decay or lessen it so that they only half by the the GM. Personally, I think TA = 3 is the best value,
time a long rest is taken, or even do not decay at but this will vary with other tables. The calculation
all (see Spell Slot Batteries). With the arcane of R is a little more complicated, as discussed in
engineering subclass, at the appropriate level, you Resistors, but to recap, we use eq. (2.22) for series
may, as an action, dump the entirety of the energy resistors (resistors that are one after the other) and
of your battery as a single attack doing 1d6 per eq. (2.21) for parallel resistors (if the wire splits and
level for each spell slot in a 15 foot cone (details rejoins before the caster).
on the attack in the next section). This means two In the below example (which will probably be
3rd level spell slots would do 6d6 damage. This more complicated than anything you should make),
effect will be fairly chaotic and so you should roll there are two casters and four resistors. In order to
for the type of damage it does using a d12 with the calculate TL for each spell caster, we need the total
following table: resistance of their path.
2 I was toying with the idea that this should be your maximum spell level you can cast such that as you gain higher spell slots

your circuits become marginally faster, but given that this effect is already fractions of a second, it seems arbitrary and a needless
complication.

22
 1 1 1
= +
RP R1 R2
1 1 1
= +
RP 1 2
(3.2)
1 3
=
RP 2
2
RP =
3
Figure 3.0.1: An example complex circuit for casting We can then combine this resistance with the first
two level 3 spells resistor (before the first split, just after the battery)
the same as before: RT 2 = 1 × 23 = 23 and thus
TL2 = 19 (3 × 23 × TA ) = 29 TA .
The first, simpler, path is shown below, where we It is important to note here that per our
follow only series resistors: definition of resistance, a resistor of value R = 1
has no effect on the current. Regardless, we can see
that the more complex path will cast first while the
simpler one will cast second. If we use my proposed
value of TA we get TL1 = 2s and TL2 = 32 s.

An Aside on Total Resistance of

Example
As discussed in Resistors by Equation (2.19),
there is a limit to our total circuit resistance we
must account for. The total resistance here is the
sum of the resistances in the two vertical paths, as
previously calculated the resistance in the left path
is RP = 32 and the resistance in the second is simply
Figure 3.0.2: The same diagram as fig. 3.0.1 with 2. We combine these using eq. (2.21):
the simplest spell casting path highlighted.
1 1 1
= +
RT R1 RP
On this path, we have two resistors, one of 1 1 3
= + (3.3)
resistance R1 = 1 and one with resistance R2 = RT 2 2
2. To calculate the total resistance according to 1
RT =
eq. (2.22) we simply have RT = ΠN i=0 Ri = R1 × R2 = 2
1 × 2 = 2, thus TL1 = 19 (3 × 2 × TA ) = 69 TA = 23 TA . Lmax Lmax
Since is 3 we satisfy RT ≤ L .
In the second path, we have three resistors: L

Simplified Rules
The above is...rather complicated if you’re planning
to use this in any given scenario. While I think they
are better and if you’re willing to put in the effort
to calculate specific timings, your GM should allow
it, however, no one wants the game to come to a
screeching halt because you need to run a quick
calculation. The simpler form of the rules that
you will be able to simply calculate (even if it isn’t
Figure 3.0.3: The same diagram as fig. 3.0.1 with technically correct) is that the time delay out of
the more complex spell casting path highlighted. combat for each caster is a number of seconds equal
to the product of resistor levels before it. Obviously
this means that you can’t use parallel resistors, but
While this might seem complex at first, we can it does simplify everything to a more manageable
break the problem down. First, we will calculate degree.
the resistance after the first split (i.e., across the
two parallel resistors). As discussed previously In Combat Rules
in Equation (2.21), we can calculate this total What about during combat? Well, now we have
resistance (RP ) as: covered the basics, this is but a small modification

23
 that accounts for initiative. We simply calculate material for purchase as many of the construction
the time as we have before, but this time, we round materials are not found in the correct purities in the
to a whole integer. We say the spell is cast at the wild.
initiative order TL after the initiative step it was Arcane Engineers can also craft their own
activated. Circuits always go at the end of that components given enough time. Using approximately
initiative’s order (i.e., creatures and players go first), one hour of down time they can create components
and if there are two circuits on the same initiative at the level of:
value, then the one that was activated first will
go first. So, in our example, if we were in combat Component Crafting Cost
and activate the circuit on our turn, the shorter Capacitor 1GP ×L
delay (TL = 23 ) will happen on the initiative step Battery 5GP ×L
immediately following our turn, and the longer delay Resistor 6GP ×L
(TL = 2) will happen two steps after our turn. Inductor 20GP ×L
This might sound counter-intuitive and strange,
Table 3.4: Guide to cost of crafting components in
and that’s because it is. By my understanding of
down time where costs cover the necessary materials.
the base rules an entire round in 5e combat lasts
L here stands for the level of item being crafted or
6 seconds. Regardless of if there are thousands of
purchased.
combatants or two, they will take 6 seconds to all
take their turns; this isn’t an exact science and so
this rule-set, while not technically the most accurate, This table also acts as a guide for the cost of
allows for Arcane engineers to plan their turns purchasing these components. The maximum level
with their delayed circuits. Similar to the out of that can be crafted by an arcane engineer is equal to
combat scenario, we can simplify this to be their maximum spell slot level.
a position after you in initiative equal to the As discussed previously in Casters, Arcane
product of resistor levels before each casting Engineers can also craft their own casters.
component.
I think the simplified rules will work well for most Spell Casting, Traps, and
tables, but you may wish to talk to your GM about
implementing components such as timers or fuses to Learning
allow for longer delays. I debated this mechanic for a long while, but think
I have settled on what makes the most sense to
Cost of Components and me. Spells cast through an arcane circuit behave
very similar to regular spells (with regards to
Component Crafting casting and what the player must roll). When a
spell which would normally require a spell attack
Like all magic items and necessary equipment, this is made through an arcane circuit you designed
comes down to your GM’s discretion, should they then you will simply make it as a spell attack
think you are overpowered, they may restrict the with your modifiers. This means, since the arcane
supply. If you ask nicely and they feel you have engineer is a wizard subclass, you would be using
earned it, the supply might become more generous. your intelligence ability to calculate trajectories of
Personally, I think components should be broken your attack. Similarly spells which require choices
into levelled kits, each costing approximately double of target creatures/people or locations for casting
of the last. These will contain necessary components will work identically to as if you cast them normally
for a given level and their rarity determines the (except for the fact they are in a circuit and the
contents for said level, this rarity similarly increases timings might be a bit different). If your circuit
the cost. A nice and simple method might be to requires more manual aiming and is being used by
have a price per kit and a price per rarity, and to another creature or person then they may make a
simply add them together to get the final price ranged attack using the circuit as well as making the
of a kit of a given level and a given rarity. In the necessary selections.
following table I will give an example price guide for Concentration checks, as discussed in Inductors,
this (but you are more than welcome to change this will be made by the inductor and the circuit rather
to suit your world and players). than by you, where the modifier is determined by
This is, obviously not perfect and I think a little the inductor level.
bit restrictive, so your players should of course also Where things get a little more interesting is the
be able to buy components individually. For such presetting of arcane traps. This can be done in a few
things, the above table can be a guide for their ways but I think the easiest is that the target must
rarity and cost. In general, higher level components be predefined. For a spell which makes an attack,
should cost exponentially more than their lower you can say whether it will attack the nearest
level versions, and should be significantly more rare. creature (for example), or perhaps the biggest (it is
Similarly, these can only be created (barring any up to your GM if you can add in flavour for devices
abilities from the arcane engineer subclass) in urban such as “creature mass estimators” to your circuits if
environments or places with large supplies of magic you want some extra fun). For spells which target a

24
 Rarity I (10GP) II (20GP) III (40GP) IV (80GP) V (200GP) VI(400GP) VII (800GP) VIII (2k GP) IX (4k GP)

Common (0,3,3,3,0) (0,3,3,3,0) (0,2,2,2,0) (0,1,1,1,0) (0,1,1,1,0)

(10GP)

Uncommon (0,4,4,4,1) (0,4,4,4,1) (0,3,3,3,0) (0,2,2,2,0) (0,2,2,2,0) (0,1,1,1,0)

(50GP)

Rare (3,4,5,5,1) (3,4,5,5,1) (0,4,4,4,1) (0,3,3,3,0) (0,3,3,3,0) (0,2,2,2,0) (0,1,1,1,0)

(500GP)

Very Rare (3,4,5,5,1) (0,4,4,4,1) (0,4,4,4,1) (0,3,3,3,0) (0,2,2,2,0) (0,1,1,1,0)

(1k GP)

Legendary (3,4,5,5,1) (3,4,5,5,1) (1,4,4,4,1) (1,3,3,3,1) (1,2,2,2,1) (1,1,1,1,1)

(10k GP)

Table 3.3: A table showing example kits of arcane engineering components where the number in the brackets
tell us the number of (Capacitors, Batteries, Resistors, Casters, Inductors) in each kit respectively. The
column tells us the level of kit (and hence of components) The price of each kit is given by the sum of prices in
the level and rarity labels (e.g.Legendary Level 9 kits will cost 14,000 GP).

specific creature (such as “charm” for example), you

may choose to have targets such as “The first person
to touch the object.” For Area of Effect spells you
must preset the location at which the spell will be
cast (within range of course).
These are all fairly reasonable assumptions to be
made and allow the system to work with the myriad
of different spells possible. Once the trap is set I
believe you would have to disarm the trap if there
are relevant materials (i.e., pressure plates), maybe
if your GM is nice they will give you advantage since
it’s your own trap.
If a spell requires a target it can “see” then the
casting component must be able to draw a direct
line of sight to the target.

Concentration
Spells which require concentration require an
inductor in the circuit of equal or greater level to
the spell being concentrated on. When the circuit
is damaged it will make a constitution saving throw
with a modifier equal to the inductor’s level.

Counter Casting
Nice and simple: effects which dispel magic will
result in the circuit not being able to cast, it will
lose all spell slot charges stored in the battery, if you
are a nice GM you may allow for components which
grant some resistance to this effect (i.e., the circuit
cannot cast but it will not lose any spell slots unless
activated at which point it will lose the cast spell
slot). Counters to spell casting specifically also work
provided they satisfy the rules as if the circuit had
cast like a creature, any associated checks or saves
will be made by the arcane engineer as a stand in
for their technical ability to craft resilient circuitry.
Since the casting components are neither verbal nor
somatic they are resilient to counters which typically
silence spell casters.

25
 Arcane Engineer Spells and Stabilise
3rd level Transmutation
Actions Casting time: 1 action
These are few since the arcane engineer is a subclass Range: Touch
of wizard and thus uses the wizard spell list. That Target: An arcane circuit which you touch
said there have been some specialised spells that any Components: V
wizard can learn but are of particular use to Arcane Duration: Instantaneous
Engineers. Classes: Wizard
You touch an arcane circuit built by a willing
Repair Circuitry creature and immediately shield it within a
1st level Transmutation protective sphere. While in this sphere the circuit
Casting time: 1 action cannot cast spells and has an additional +10 to
Range: Touch its AC and advantage on all saving throws. If the
Target: An arcane circuit which you touch circuit drops below 0HP while within the sphere it
Components: V, S, M (spare arcane wire) will return to 0HP at an initiative of 20.
Duration: Instantaneous
Classes: Wizard Battery Dump
An arcane circuit you touch repairs itself with You may use an action to dump all remaining spell
your touch gaining a number of hit points equal to slots from your arcane battery you can touch into a
1d4 + your spellcasting ability modifier. This ability 15 foot cone originating from your circuit. Creatures
has no effect on creatures which are not constructs. within the cone must make a Dexterity saving throw.
At Higher Levels: When you cast this spell A creature takes 1d6 damage for every level of each
using a spell slot of 2nd level or higher the healing spell slot on a failed save and half as much on a
increases by 1d4 for each slot level above 1st. successful one.

26
Circuit Rules Cheat Sheet
This is a simple rule sheet to cover all the • Out of combat: The spell will cast at a
rules required of circuit building so that both the number of seconds after activation equal to the
player and GM can check that circuits are valid total resistance before the caster component.
by the rules we have ascribed. These are the most
simplified rules from the theory developed. There 4. Inductors
is more nuance available in the sections above,
1. Inductors must be equal to or greater than the
but these should allow for quick building and
spell level passing through them.
calculations.
2. When a concentration saving throw is required, it
1. General is done with the usual rules with the constitution
1. All Component Levels must be less than or equal modifier of the circuit being equal to the
to the maximum spell slot level of the circuit’s inductor’s level.
creator.
3. Two inductors of inductance L1 and L2 may
2. All circuits must contain a battery (or capacitor) transform from spell slots L1 → L2 according to
which is connected to a caster. If that battery is L2 = LL1 L1 .
2

above 0th level the circuit must have a closed loop

back to the battery. 4. Inductor based transformers require:

3. Spell slots of different level cannot pass through L2 ≤ L1 s.t. L2 ≤ L1

the same wire but can exist in the same circuit.
4. Circuits cannot cast ritual spells. 5. Casters
5. Only Arcane Engineers may charge batteries with 1. Casters may cast any preexisting wizard spell in
their spell slots. Charging a battery takes one 5e
entire turn.
2. If the circuit is not equipped to a creature, the
target(s) of a spell must be preset in general
2. Spell Slot Storage terms5 .
1. Spell Slot Batteries lose their charge after a long
rest unless they are special components that 3. Spells will cast immediately when a full spell slot’s
negate this rule. worth of energy is in the caster component and
not sooner or after.
2. Spell Slot Batteries may only hold spell slots of
level equal to theirs. Functionally the amount is
beyond the limit of any caster but for edge-cases,
Building Rules Checklist
we say a battery can hold 10 spell slots. Reiterating the rules relevant to circuit building: a
circuit is stable if it satisfies the following:
3. Spell Slot Capacitors may only hold one spell slot
of level equal to theirs. □ All Component Levels must be less than or
equal to the maximum spell slot level of the
4. Different spell slot levels cannot be present in the circuit’s creator.
same wire at the same time.
□ All possible paths begin and end with the same
3. Resistors battery (a closed loop) with the exception of
0th level batteries.
1. The resistance along a given path3 ‘R’ must
□ Different spell slot levels cannot be present in
satisfy R ≤ L9 with ‘L’ equal to the level of spell
the same wire at the same time.
slot passing through the resistors.
□ The resistance along a given path3 ‘R’must
2. The delay of any particular path is calculated satisfy R ≤ L9 with ‘L’ equal to the level of spell
by multiplying the individual resistance along slot passing through the resistors.
said path. If the battery’s spell slot energy is
split along multiple paths then the time will be □ Inductor level is greater than or equal to the
multiplied by the number of paths the energy is spell level it will be casting.
split between4 . □ Transformers can only downgrade spell slots.
• In combat: The spell will cast at an initiative If the circuit fails to meet these requirements,
after the circuit is activated equal to the total then when the circuit is activated, you must roll on
resistance before the caster component. the Chaotic Circuit Failure Table (Next Page).

3 Calculated by multiplying the individual resistances

4 So if my level 1 battery is powering two casters it will take twice as long for both to cast
5 e.g. “The nearest three creatures”

27
 Chaotic Circuit Failure Table
This is a simple table that you must roll on if you break the rules of circuit construction or your circuit suffers
a catastrophic failure. After every effect, the circuit becomes inoperable unless otherwise stated.

Chaotic Circuit Failure Table

d100 Effect d100 Effect
01-02 Roll on this table at the start of each of your turns for the next minute, ignoring 51-52 Roll a d8, that number of components in your circuit fail starting from the first
this result on subsequent rolls. component after the highest level battery and moving along the circuit.
03-04 The wire of the circuit begins to heat, resulting in 1d4 fire damage to the circuit 53-54 An adhesive substance appears on your circuit, sticking it to whatever creature or
and anything touching it. object it is closest to for the next hour. It cannot be removed by any means until
the hour is up.
05-06 For the next minute, you can change the spell cast through the spell caster at will 55-56 The wires in your circuit burn out, and any creature touching the wires takes 1d8
to a spell of equal or lower level; after this minute, the caster will break and be fire damage, and the circuit is unusable until new wires are installed.
unable to be used until replaced or repaired.
07-08 A light-blue magic flare illuminates a region up to 30 feet around the circuit in 57-58 The circuit fixes itself such that it no longer violates the rules at no cost to you.
light, clearly visible to any creature with line of sight within 500 feet.
09-10 Magic Missile is cast from each spell battery at the batteries level at a target of 59-60 For the next minute, the circuit will change colours, cycling through the rainbow
your choosing. and back.
11-12 The range of spells cast through this circuit increases by 10 feet for a minute. 61-62 The circuit will release a brilliant bright light, blinding every creature within 30 feet
of it if they fail a Constitution saving throw with your Spell Save DC.
13-14 The wires of the circuit glow, illuminating everywhere in line of sight with the 63-64 The circuit creates an arcane fog centered on itself that is the equivalent to casting
circuit. Fog Cloud.
15-16 The Circuit casts Thunderclap centered on itself. 65-66 For the next minute, the circuit has effectively no weight.
17-18 The wires of the circuit begin to grow in length, dangling from their attached 67-68 For the next minute, Silence is cast centered on the circuit and moves with the
components. Any creature which was holding the circuit must make a Dexterity circuit.
saving throw against the circuits DC. If they fail, they will become restrained. They
may make a new Dexterity saving throw at the beginning of their subsequent turns
until they succeed.
19-20 The resistance of all resistors in the circuit become one, but the circuit does not 69-70 The circuit will do nothing until the start of your next turn, at which point, it will
break until after the casting. cast as expected.
21-22 For the next minute, the weight of the circuit doubles, causing the wearer (if any) 71-72 For the next minute, the circuit grants you some of its arcane power, giving you
to have disadvantage on all Strength and Dexterity saving throws. advantage on all Intelligence and Charisma saving throws.
23-24 The Circuit and the material it is attached to become invisible for the next 10 73-74 For the next minute, the circuit releases random sparks, and if a creature enters or
minutes. starts their turn within a 10 foot radius of the circuit, they must roll a Constitution
saving throw with DC equal to your own spell save DC, taking 3d4 lightning
damage on a failed save and half as much on a success.
25-26 For the next minute, the circuit becomes a creature that is passive and casts the 75-76 You may choose to either roll on this table again or take 1d4 fire damage.
same as before...just now, it looks and feels alive, with casters appearing like eyes.
After that minute, the circuit dies and is not repairable. It keeps the AC and HP of
the circuit it came from.
27-28 For the next minute, any initiative delays to casting are halved, and activating the 77-78 For the next minute, any initiative delays to casting are doubled, and activating the
circuit now takes a bonus action. circuit now requires an Action and movement.
29-30 The circuit teleports 60 feet to an unoccupied location in a direction determined by 79-80 When you cast the next spell, the circuit will cast as many spells as there are spell
the result of a d4 roll (1 = forwards, 2 = right, 3 = behind, 4 = left). Otherwise, it slots remaining in its battery such that it targets the maximum number of different
is unchanged. creatures, beginning with the one closest to it. If the spell has an Area of Effect
they can be placed where the activator of the circuit chooses to target the largest
number of targets possible with overlaps where possible.
31-32 The circuit is transported to another plane until the end of your next turn, after 81-82 The circuit vanishes, and all components are lost.
which time it returns to the space it previously occupied or the nearest unoccupied
space if that space is occupied.
33-34 The next damaging spell cast through this circuit deals maximum damage. 83-84 The circuit assumes the shape of a sphere, and if it was wrapped around any part
of a creature (e.g., finger, arm, or head), they will take 2d8 bludgeoning damage.
35-36 The circuit begins to rust and wires will require replacing; until then, the circuit is 85-86 The caster nearest the circuit restores one spell slot of equal level to the lowest level
inoperable. spell slot battery in the circuit.
37-38 For the next minute, the circuit can fly and behaves as a creature controlled by the 87-88 The Circuit turns to water permanently, losing all components.
GM with a flying speed of 40 feet; it is frightened of you. If it is attached to you,
then you must make a Strength Saving throw to resist its desired movement.
39-40 The circuit, through highly improbable magic effects, grants you another spell slot 89-90 The circuit becomes confused and tries to pass lightning through its wires. Any
of equal level to its lowest battery level. creature touching any wire in the circuit must make a constitution save taking 3d8
lightning damage on a failed save and half as much on a success.
41-42 The Circuit transforms into a plant-like creature that behaves as the circuit 91-92 The base object of the circuit is transformed into a mimic.
normally does (i.e., it still functions) until the next long rest is taken at which
point it decays and is not repairable.
43-44 For the next minute, the spell cast by this circuit does not consume spell slot 93-94 The circuit turns into a single gold coin, destroying all components in the process of
charges from the battery. its transformation.
45-46 For the next minute, the caster will cast Magic Missile at the level of battery 95-96 The circuit begins to emit a high pitched buzzing that only you can hear for this
provided. If the battery is level 0, then only one dart is cast. turn, and next, you will take 1d4 psychic damage.
47-48 For the next minute, the circuit can speak and may choose not to cast its spells. 97-98 You so fundamentally break the fabric of magic around you that no spells may be
You may attempt to convince it with persuasion or intimidation skill checks with a cast within 60 feet of the circuit for the next minute.
DC equal to your spell save DC.
49-50 All components become gold, each worth about 50GP. After 24 hours, the 99-00 The circuit immediately casts all the intended spell(s) of the circuit on itself
components will return to their normal material, and if the circuit has not been simultaneously.
altered, it will return to functionality again.

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Chapter 4: The Arcane Engineer Subclass
As an Arcane Engineer, you seek the mastery DC. The circuit must follow the standard rules of
of the practical application of magic theory. More circuit construction, and you may only have one
traditional wizards might look upon your work as of these circuits at any given time. Only you may
strange and dangerous when compared to the more use this circuit and it does not interfere with other
traditional specialisations of orb ponderers, pointed circuits. Once per long rest, you may reconfigure the
hats, and heavy books. Non-wizards might see your circuit and its components however you like.
rules as an unnecessary restriction on their more
chaotic constructs. In reality, you know that it
is through a careful understanding of these rules
you can bring the consistency and danger of a well-
trained wizard to the creativity and practicality of
real-world systems. Upon taking this subclass, you
learn the action Battery Dump (see above).

Component Savant
You’ve begun to familiarise yourself with the
components of your circuits, their theory, and
their materials. Using this knowledge from second
level and higher, you can create circuits provided
you have the correct components. Crafting and
purchasing components is limited to areas with
sufficient materials such as urban environments or
locations with sufficient materials in the correct
quality for components.
Additionally, you may also repair a circuit which
has had its HP drop below 0 provided it has not
dropped below the negative of its maximum HP.

Component Specialist
Starting at sixth level, you may increase the level of
components not embedded into circuits by one for a
quarter of the standard cost (given in chapter 3) of
constructing a component at this higher level. You
may upgrade a component as many times as you like
up to a level equal to or less than your maximum
spell slot level.

Scavenger
Your deep understanding of the components that
build magic circuits allows you to find suitable
replacements from your surroundings without the
need to purchase or craft new components. Starting
from tenth level, you may use a day of down time
to find 10GP worth of component equivalents at no
cost to yourself. These equivalents can be found in
all environments and will act exactly as a normal Art Credit: George Eracleous
component would.

Theorist
At levels 14 and higher, your understanding of magic
circuitry is so deep, you are no longer bound by
the material costs of components; instead, you can
create a theoretical magic circuit on a chosen object
that acts exactly the same as a physical circuit
would. To see the circuit a creature must make an
investigation check with DC equal to your spell save

29
30
Chapter 5: Arcane Engineering Examples
Background
The following are example circuits taken from one of the university’s top professors Elyn Sparkfire. Her
scrawlings have been found on various blackboards, scraps of paper, walls, books, desks and occasionally
students around the University of Theoretical Magic. Despite her...eccentricities...she has pioneered the field,
and it would not be right to ignore her contributions. In each section, I will describe the circuit, its workings,
and the circumstances in which we found them. Please use at your own risk.

Bait and Blast Brief Glimpse

The Bait and blast was proudly displayed (without I found a box on my desk one day containing this
my prior knowledge) at the first ever convention circuit. The “Brief Glimpse” first casts Foresight on
for limiting magic’s use in warfare. Elyn told me the person to first touch the box. It then, almost
she planned on demonstrating the risks of arcane immediately after, casts Power Word Kill. Naturally,
engineering’s contributions to warfare, and to her being the middle of a work day, I was in good health
credit, she certainly made her point. and not affected by the spell. I was, however, quite
Built into a throwable object, the Bait and affected by the howling laughter of Elyn as she fell
Blast is comprise of two connected circuits. Both out from her hiding place in my office, spluttering
are activated by a simple switch, though I’m told out the words, “You should have seen your face!”
a sensor or other cantrip-based detector would between her cackles. I did not find it as funny. Very
work. When the button is pressed, the cantrip dangerous circuitry.
energy is passed to both circuits and through the
AND gates, allowing their spells to pass. The
first (top) circuit uses a 6th level battery to cast
Mass Suggestion with the predefined suggestion
“Approach.” Unsuspecting victims will then walk
towards the device. The second (bottom) circuit will
then cast fireball on itself, destroying the device and
anyone nearby. The third level resistor slows the
casting just enough for the approach command to
take effect. After we had quite securely drained the
batteries at the convention, Elyn decried the lack of
1. A more effective low level area of effect spell for
which to attack the victims.
2. A lower level, less long lasting, version of Mass
Suggestion which might allow for construction
that less valuable resources.
Needless to say, I checked Elyn’s work before any
future displays.

Clown Buzzer
A favourite of Elyn’s at formal occasions, a simple
cantrip battery takes energy from the surrounding
environment, and channels it into a shocking grasp.
Very funny to the right crowd.

31
 Chaos it will cast banishment, keeping concentration using
the inductor. I’ve been told this should give them
When I first saw this diagram on the blackboard of ample time to reconsider their lordliness.
Elyn’s lab, I assumed it was a simple mistake. It
was only when I heard the thud of six magic missiles
(a 9-10 on the Chaotic Circuit Failure Table) and
her triumphant shouts, I realised what she had done.
The circuit is DESIGNED TO FAIL to induce
one of the chaotic effects arcane engineering can
lead to. The fourth level spell slot backs up at the
third level resistor, resulting in a build up of magical
energy. If it somehow doesn’t fail, it still casts
Blight, a strangely dangerous choice. I believe the
goal of this research was to find a way of inducing
certain chaotic effects more often than others, but to Delayed Dispel Magic
date, this research has not yielded expected results. This is actually one of Elyn’s latest inventions after
a few grumblings from some of the other academics.
This is an emergency magic dispelling circuit that
can be activated manually, giving a short delay and
then casting dispel magic. The delay is so that the
item may be thrown or allow someone relying on
other magic to get out of the dispelling field’s way.

Charming Ring DO NOT PRESS

A fantastic ring that I must admit to having
borrowed for one or two important meetings. A Elyn has recently been trying to work on her cross-
simple contraption, small enough to fit on a ring disciplinary research, and this was her attempt at
and appear stylised, it will cast charm person on the something called “psychic-ology.” She placed this
person who activated it (likely during a handshake circuit in the centre of the student halls along side
or other greeting). a large magic sign saying, “DO NOT PRESS.” She
aimed to show how trustworthy both our signs
and students are. When the button is pressed, it
casts shatter at 9th level. She is very lucky it was
Wizard Wenda who pressed this first and not one
of our more fragile students. Wenda was simply
enraged and cast “Hit with Axe” a few times.
Which reminds me to follow up on exactly what her
qualifications were.

Crown of Banishment
When she was reading too many fantasy novels,
Elyn created this as a trap for any descendant of
exiled kings. “You know, the type that roam around
with birthmarks and swords, joining humble jobs
like the city guards until one day they slay a dragon
and overthrow whoever ran the city before,” she told
me. The wearer sees this crown, but unless they are
observant enough they will not notice the circuitry
hidden on the inside. When they put the crown on,

32
Firefighter
One of Elyn’s most useful inventions. A smoke
detector allows cantrip level energy to pass to the
AND gate if it detects any smoke; this then allows
a fourth level battery to cast control water on a
nearby reserve, which is directed to the source of
the fire. I have personally seen to it that these
have been installed in our most flammable labs and
library sections.

Grease Trap
Elyn had this brilliant idea while discussing food
preparation within the university. The circuit
simply activates when a pressure plate is stepped on,
first casting grease, then almost immediately after
casting produce flame with a one-second delay. This
was not intended for use in kitchens.

Fire Grenade
In protest of the number of her resources used
to put the “Firefighter” circuit throughout the
university, Elyn created the “Fire Grenade.” It
begins with the pin switch closed, which stops any
current passing from the NOR gate. You then press
the button (similarly preventing the NOR gate from
giving an output) and then release the pin. Now,
when you release the button, there will be a four-
second delay. After this, the AND gate will activate
and the third level fireball will undergo another
three-second delay before casting. This allows for
the object the circuit is built into to be thrown.
Say what you must, but there is no doubting the
effectiveness of Elyn’s work.

33
 Hand-held Fan
The first time I became aware of this invention was
during a warm summers day when Elyn and I were
strolling through the campus. Being far too warm,
she produced a hand held fan; unfortunately, I was
not paying enough attention and only noticed the
circuit as we were both thrown 15 feet across the
green. She has assured me she is looking into a
way of reducing the impact of the gust while still
keeping the circuit handheld. That said, the alchemy
department have put this to great use.

Labyrinth
This was one of Elyn’s earlier “pranks” for another
member of staff with which she had had enough.
The “Labyrinth” first casts Feeblemind on the target
foolish enough to press the button before Maze is
cast on them. Trapping them until the spell ends.

Little Big Light

Hot Potato A charming device Elyn uses at her desk when
While explaining the power of non-magical marking. With a simple switch, the object will
suggestion during a lecture, a student insisted either cast light or dancing lights depending on
she was wrong. In response, Elyn reached into how much light she needs for her work. I recieved
her drawer and withdrew this brass ball, shouting a similar circuit for my anniversary of ascension to
“catch!” at the student, and then subsequently filling Archmage and am thrilled.
out a lot of paperwork and a handful of written
apologies to everyone involved.
Initially, the cantrip capacitor is uncharged and
the button open, which stops the AND gate (A and
B) from activating. After pressing, the capacitor
charges, but the NOT gate inverts the signal again
keeping the AND gate off. After the button is
released, the cantrip signal from the capacitor and
the NOT gate allows the signal to flow, casting
heat metal on the ball it is built into. In layman’s
terms, if you press the button then release, it will
get dangerously hot. Elyn would like to reiterate
how sorry she is to the students affected and how Might Explode
much she has grown as a person during her resulting Elyn’s most terrifying invention to date, simply
temporary suspension from teaching. because even she refuses to test it. A funnel

34
containing some flammable liquid (e.g., lamp oil)
is held in a high place like a ceiling. A small glass
plate prevents fuel from leaving. With the press of
a button, the right hand circuit creates a flame and
the second casts telekinesis, which pushes the glass
plate aside, allowing the fuel to fall. Her concern is
that the fuel may catch inside the reserve as it is not
falling fast enough, so instead of having the desired
effect of dropping liquid fire onto her victim, it may
cause an explosion, which is “no use at all.”1

Nuclear Option
Elyn proposed this to me during a staff meeting
once, and I hope she hasn’t begun construction
and never will. The circuit is comprised of as many
Ninth level batteries as you can find, each casting
meteorswarm at a predetermined location. In
order to switch on, the master AND gate must be
activated by the turning of two keys. She suggested
I have one and she have the other, which is a much
better idea than her having both (or the only) keys.

Missile Stick
A simple but cunning invention styled to look
like a standard wizard’s wand but significantly
less versatile. By a radial switch, you can select
the level of magic missile you wish to cast. A
favourite of our one and only Reliable Ron, who
insists on only casting Magic Missile. The power
of this device seems to mostly be in the reliability
of its application within other circuits and as a
demonstration of the use of switches.
1Were you to use this in game, I’d say that it has to “succeed” a +0 saving throw against its creators spell save DC (i.e., the

circuit wants to explode, but only if it’s clever enough to circumvent design).

35
 Opus Lux
A fancy old language for “Work Light”, this orb sits
in the center of Elyn’s work bench. When activated,
it will cast Light and Levitate on its own casing,
floating above her station and providing a bright
light from which to work.

Reactive Armour
In her aforementioned fixation on fiction novels,
Elyn decried her inability to effectively use plate
armour due to her “academic levels of strength.”
When I pointed out that we have Mage Armour, she
frustratedly said that it required you to cast it when
the time was right rather than when you needed
it...at which point, she ran off to her workshop.
This is a simple ring or brooch over an area of
interest where a sensor detects blood and casts
Mage Armour. While I’m sure some battle mages
might find this helpful given Elyn’s broader lifestyle,
this has mostly resulted in her gaining armour after
giving herself a paper cut.2

Parachute
A small detector inside this device detects whether
the object is or is not in free-fall and, if it is,
casts feather fall on the nearest creature. I only
discovered this when Elyn leapt from one of the
tallest towers of the university and landed with some
grace about 300 feet below her. While it doesn’t
have any damaging components, it certainly inflicted
some sort of psychic damage on me.
Spell Counter
A now commonplace circuit amongst our graduates,
the spell counter detects perturbations in magic
fields and casts counterspell. This doesn’t always
work, of course, as the circuit may not be able to
see the caster. Regardless, it will also give a light
indicator to the user to say that a spell has been (or
attempted to be) countered. This is especially useful
if you intend on adventuring in high risk regions.

Passwall Button
For years, Elyn used buttons like these she had
hidden around the university to get around without
being pestered by students, staff, or anyone else.
While I don’t condone such behaviour, it has been
exceptionally useful to know the location of a few of
these. By my count, there are currently thirty-six
hidden within the campus.
2 In game I would take this as undergoing slashing, bludgeoning, piercing, or force damage.

36
The Box The Useless Machine
Regretfully, students will sometimes disagree with A fun side project she has every student make in
their lecturer’s grades and challenge them. In this their first advanced class. A simple machine which
particular case, a student challenged Elyn who had casts telekenisis to shut itself off. Fascinating, if
failed them for “Not considering all eventualities.” useless.
She decided to give the student a final chance, and
they could make any contraption they wanted to
and try to escape whatever trap she made, and if
they did, she would pass them. Assuming she would
simply make some form of counterspell device, they
opted to avoid any teleportation magic and instead
decided to make a counter-counter spell circuit to
win this “duel.” Clearly, they had not been paying
attention to who was lecturing them as they failed Vendor
to counterspell one of the four walls that erupted To help raise funds for certain faculty events, Elyn
around them. This device is a little too flashy and made this, an automated arcane vendor. which will
irregular for my tastes, but I do enjoy a tale of dispense food and drink when provided with coins.
hubris. Were I to remake this, I would simply choose This has proved a highly successful way of earning a
one type of wall. passive income.

The Scary Orb

This was actually Elyn’s first ever contraption which
she made as an undergraduate. Mostly used to keep
away the folk she didn’t want to be near, ‘The Scary
Orb’ simply detects intelligence3 and casts in their
general direction. She still carries this orb at the end
of her staff to this day.

3 For a game rule, I would say its a simple 1d20+0 check for the circuit to detect the target with a DC of 10 minus target’s

intelligence modifier (i.e., smarter people are easier to detect).

37
 What Was Tha-
This circuit is used to help teach students the
importance of comedic timing. When the pressure
plate is pressed, there is a three-second delay
followed by a fireball. Elyn says it is an important
Arcane Engineering principle to be able to
anticipate the words that your targets will say as a
good punchline will ensure maximum effectiveness.
I’m not sure I agree, but the results speak for
themselves.

38
Chapter 6: Acknowledgements
In particular, I would like to thank Stenis for his work on the background graphics, foreground graphics (such
as the Theory of Magic logo), and circuit diagrams in the final chapter. Graphic design is not my passion but
I’m very fortunate to know people for whom it is. While the effect of the background graphics and the footer
are subtle they add a huge amount to the overall feeling and impact of the work. You can see his other work at
his twitter: ‘@__stenis__’ or his Bluesky: ‘@stenis.bsky.social’.
I would also like to thank George Eracleous for his incredible cover art, component sketches, and concept art
for the Arcane Engineer subclass. Be sure to check out his artstation (https://www.artstation.com/theredcow).
One of the great joys of this work is getting to talk to so many talented people and coordinate their talents
into my mediocre ideas, which I always feel gives these things a veneer of professionalism I have not earned.
I’d also like to thank my editors. There were three that had the misfortune of working with me. My
apologies to the editor who simply had to check for grammar and spelling. I seem to view grammar as a series
of suggestions rather than rules that helps readers, and so they found 600 places where I needed to put
commas. Secondly, I had an electrical engineer review my real-world introductions, mostly so I had someone
else to share the blame with for my own idiocy. Finally, and certainly not least, I would like to thank Jesús
Blanco Artero for his incredible work helping me balance the game-play applications of this work. I wish I
could pretend I had thought of every eventuality and come up with good systems first try, but alas I am
stupid. Jesús found a lot of areas for improvements in my rough foundations, and with our constant back and
forth we were able to come up with a system I’m very happy with. Especially for systems like the custom
casters, you are seeing a large amount of work from him.
Lastly, I’d also like to thank you and all the other readers for your continued support of my various works
and patience with how long it takes to write. Hopefully, you will continue to enjoy the nonsense I write in the
future. I’d appreciate if you left a review, but a lot of this book was a lot of hard work on your part, so I don’t
think I can ask you for much more than that.

39