Double tool upgrade using 4PDT relay. #151

Arnaud-ChevalierDWW · 2026-04-05T14:46:17Z

Arnaud-ChevalierDWW
Apr 5, 2026

Hi, I made this dual-tool upgrade for AxxSolder, as I often need two different irons. It uses a 4PDT relay. I use a geeboon stand and handle, for people using other brand a 5PDT might be needed.

video of the iron working
photo :

An improvement could be made to prevent switching while a handle is powered. That would help avoid damage caused by user error.

If the upgrade proves to be stable and there is interest, I will upload the files here : PCB, CAD files and materials used.

Have a great day!
Arnaud

AxxAxx · 2026-04-07T06:05:47Z

AxxAxx
Apr 7, 2026
Maintainer

Very nice idea!

Maybe you can use the "GPIO4 ON at run" and the GPIO4 to know when AxxSolder is in running state.
And where does the switch signal come from?

4 replies

Arnaud-ChevalierDWW Apr 7, 2026
Author

Hi!

Yes, very good idea! I guess that could be achieved with a mosfet, blocking 24V to reach the relay. Opposite logic as when using GPIO4 to run a fume extractor.

The switch signal comes directly from the 24V power supply, controlled via a switch on the enclosure.
I uploaded a short video of it in action, maybe you missed it.

AxxAxx Apr 17, 2026
Maintainer

even the USB could be used to connect to the relay module if you do not want to solder. the USB connector D+ and D- is basically just connected to PA11 and PA12 and not used during normal operation. Only used for firmware flashing in bootloader mode.

AxxAxx Apr 17, 2026
Maintainer

so a usb-c to usb-c cable between the relay board and AxxSolder would give you 2 GPIO's to play with

ct2iry-dot May 24, 2026

even the USB could be used to connect to the relay module if you do not want to solder. the USB connector D+ and D- is basically just connected to PA11 and PA12 and not used during normal operation. Only used for firmware flashing in bootloader mode.

Hi AxxAxx,

Following the conversation with Arnaud
about the handle switch — great suggestion
on the USB-C GPIO trick and GPIO4 protection!

I am planning to extend Arnaud's design
to 4 channels (3 irons + tweezers):
CH1: T245 ← general work
CH2: T210 ← SMD/PCB
CH3: T115 ← micro SMD
CH4: C120 ← tweezers (JBC AM120 compatible)

GPIO plan:
PA11 → CH1 via USB-C ← no soldering ✅
PA12 → CH2 via USB-C ← no soldering ✅
USR_2 (PB0) → CH3 ← solder pad ✅
USR_3 (PB1) → CH4 ← solder pad ✅
USR_4 (PB2/GPIO4) → MOSFET protection ✅

Pre-heat discovery:
HF18FH NC contacts implement pre-heat
passively with zero extra components:
NC closed (inactive) → resistor → 150°C ✅
NC opens (active) → AxxSolder takes over ✅
= true JBC behaviour ← no extra hardware ✅
24V already present on Arnaud's PCB ✅

A few questions:

PA11/PA12 via USB-C:
Does firmware need changes to configure
PA11/PA12 as GPIO outputs in normal mode?
Which HAL init needs updating?
GPIO4 MOSFET protection:
Arnaud's plan = MOSFET blocks 24V to coil.
Confirm logic:
GPIO4 HIGH (RUN) → MOSFET ON → relay BLOCKED ✅
GPIO4 LOW (SLEEP) → MOSFET OFF → relay FREE ✅
USR_2/3 (PB0/PB1):
Already configured as GPIO outputs
in current firmware?
Or need HAL_GPIO_Init?
TIM2/TIM4 PWM on PB0/PB1:
For variable pre-heat temperature control
instead of fixed resistor —
are TIM2/TIM4 channels available on PB0/PB1?
C120 tweezers support PR:
I have analysed tip_profile.c and main.c.
Adding C120 support = ~40 lines:
enum handles + C120
default_profiles[] entry:
kp=6.0, ki=5.0, kd=0.4, max_i=200
TC compensation similar to T210
power limit = 65W
Would you accept this PR?
4-channel firmware PR:
Auto-select via SLP signal ✅
GPIO4 switching protection ✅
PA11/PA12 + USR_2/3 channel control ✅
Pre-heat PWM via NC contacts ✅
Would you accept this PR?
Arnaud's video:
You mentioned you may have missed it —
the link would help understand
the SS (stand sense) signal routing
since HF18FH = 4PDT = only 4 poles
and SS is the 5th signal.

I have done complete analysis of:
AxxSolder firmware (main.c, pid.c,
tip_profile.c, main.h) ✅
SW03 hardware signal architecture ✅
GPIO mapping for 4-channel control ✅
Pre-heat via NC contacts confirmed ✅

Happy to contribute all of this as PRs.

The end result would be the first open source
soldering station with true JBC-like
multi-channel pre-heat behaviour. ✅

Thank you!
Nuno — CT2IRY

ct2iry-dot · 2026-05-24T11:26:36Z

ct2iry-dot
May 24, 2026

Hi, I made this dual-tool upgrade for AxxSolder, as I often need two different irons. It uses a 4PDT relay. I use a geeboon stand and handle, for people using other brand a 5PDT might be needed.

video of the iron working photo :

An improvement could be made to prevent switching while a handle is powered. That would help avoid damage caused by user error.

If the upgrade proves to be stable and there is interest, I will upload the files here : PCB, CAD files and materials used.

Have a great day! Arnaud

Hi Arnaud,

I was thinking about a feature like that
for my own build, aiming at 3 or 4 channels —
3 different irons or 2 irons + tweezers, etc.

Since you already made the PCB, would you
share the KiCad files so we could extend
your design to 3 or 4 channels?

My target setup:
CH1: T245 ← general work
CH2: T210 ← SMD/PCB
CH3: T115 ← micro SMD
CH4: C120 ← tweezers (JBC AM120 compatible)

Now that I understand your design fully:
Relay PCB inside AxxSolder enclosure ✅
24V → toggle switch → relay coil ✅
GPIO4 + MOSFET for switching protection ← brilliant ✅

The goal is true JBC behaviour:
All inactive tips maintained at standby
temperature continuously.
Pick up any handle → instantly ready. ✅

I noticed the HF18FH/024-4Z13D has
NC contacts on all 4 poles.
These can implement pre-heat passively
with zero extra components:

Channel INACTIVE (relay de-energised):
NC contacts CLOSED
→ small resistor → 150°C standby ✅

Channel ACTIVE (relay energised):
NO contacts CLOSED → AxxSolder full power ✅
NC contacts OPEN → pre-heat disconnected ✅

= the relay itself handles pre-heat switching ✅
= no extra relay, no extra MOSFET needed ✅
= true JBC pre-heat behaviour ✅

24V is already present on your PCB ← perfect.
Just a power resistor on the NC path per channel.

For automatic GPIO control replacing
your toggle switch:
USR_2/3 → ULN2003A → relay coils ✅
PA11/PA12 via USB-C → relay coils ✅
GPIO4 + MOSFET → blocks switching while heating ✅
= same relay PCB, same enclosure ✅
= firmware controls it automatically ✅
= no switch on enclosure wall needed ✅

To move forward I need from you:

KiCad schematic ← complete circuit
especially how SS (stand sense) is handled
HF18FH = 4PDT = only 4 poles
SS is the 5th signal ← where does it go?
KiCad PCB file ← to extend to 4 channels
and add NC pre-heat resistors per channel
CAD enclosure files ← can it fit 4 relays?
or do we need a new enclosure design?
BOM confirmation ←
HF18FH/024-4Z13D = 24V DC coil confirmed?
Video link ← AxxAxx mentioned he may
have missed it — would help us all ✅

On my side I have done:
Complete AxxSolder firmware analysis ✅
GPIO mapping ← USR_2/3/4 + PA11/PA12 ✅
C120 tweezers firmware ← ~40 lines ✅
GPIO4 protection logic ✅
Pre-heat via NC contacts ← confirmed feasible ✅

Happy to help on the complete 4-channel version
with automatic switching and true JBC pre-heat,
and contribute everything back to the project
as a PR for the whole community.

The end result:
First open source soldering station
with true JBC-like multi-channel pre-heat
using hardware already on the board. ✅

Thank you for the great work!
Nuno — CT2IRY

1 reply

Arnaud-ChevalierDWW May 25, 2026
Author

Hi Nuno — CT2IRY,

That is a great idea!

Here are the files
video of the iron working

I am afraid the CAD won't be really useful as it was my first time using Freecad, so it is not really parametric. I don't think the design could fit 4 relays, but with one relay you can control 2 handles, so you probably only need 2 4PDT relay ?

SS goes through the relay with Red, green, and Handle Sense.
Blue (which is a floating ground if I remember correctly) goes straight to AxxSolder, not through the relay.

Relay : https://fr.farnell.com/hongfa/hf18fh-024-4z13d/relais-puiss-4pdt-6a-24vdc-embase/dp/4733448
Connector : https://fr.farnell.com/phoenix-contact/mpt-0-5-5-2-54/bornier-fil-a-carte-5-voies-26/dp/2776439

Let me know if I can help somehow.
Keep in mind this was my first time using freecad and kicad.

Looking forward to look at what you can do, seems really cool, especially the way it will interact with the firmware!
Best,
Arnaud

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Apr 5, 2026

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Apr 7, 2026
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