ESSENTIAL INFORMATION
BUILD INSTRUCTIONS
CHECKING YOUR PCB & FAULT-FINDING
MECHANICAL DETAILS
HOW THE KIT WORKS
LEARN ABOUT SIMPLE TIMING CIRCUITS WITH THIS
EASY BUILD TIMER KIT
Version 2.0
Easy Build Timer Essentials
www.kitronik.co.uk/2111
Build Instructions
Before you start, take a look at the Printed Circuit Board (PCB). The components go in the side with the writing on
and the solder goes on the side with the tracks and silver pads.
PLACE RESISTORS
1
Start with the three resistors:
The text on the PCB shows where R1, R2 etc go.
Ensure that you put the resistors in the right place.
PCB Ref Value Colour Bands
R1 & R2 10K Brown, black, orange
R3 47 Yellow, purple, black
SOLDER THE POTENTIOMETER
2
Solder the variable potentiometer into the PCB where it is labelled R4.
SOLDER THE TRANSISTORS
3
The three transistors are all the same type so it doesn’t matter which one goes where, so long as
they are soldered into Q1, Q2, Q3 on the board. You will notice that the transistors are a ‘D’
shape and the outline on the PCB is also a ‘D’ shape, make sure that the transistor lines up with
the markings on the board.
SOLDER THE ELECTROLYTIC CAPACITORS
4
Solder the electrolytic capacitor into C1. It is important that the ‘–’ on the capacitor lines up with the ‘-
---’ markings on the PCB.
Using an electrolytic capacitor backwards could result in it being destroyed.
SOLDER THE LED
5
Solder the Light Emitting Diode (LED) into LED1. The LED colours will be the wrong way around if it
doesn’t go in correctly. If you look carefully one side of the LED has a ¯at edge, which must line up
with the ¯at edge on the lines on the PCB.
Easy Build Timer Essentials
www.kitronik.co.uk/2111
SOLDER THE PUSH BUTTON SWITCH
6
The push button switch should be soldered into the board where it is labelled SW1. Once you have got
the pins lined up with the holes, the switch can be pushed ®rmly into place.
FIT THE BATTERY HOLDER
7
Finally you must attach the battery holder. Start by feeding the leads through the strain relief hole
next to the ‘-’ connection. The wire should be fed in from the rear of the board.
The red lead should be soldered to the ‘+’ terminal (also marked with text ‘red’) and the black lead
should be soldered to the ‘-’ terminal (also marked with the text ‘black’).
Checking Your Timer PCB
Check the following before you insert the batteries:
Check the bottom of the board to ensure that:
All holes (except the 4 large 3mm holes) are ®lled with the lead of a component.
All these leads are soldered.
Pins next to each other are not soldered together.
Check the top of the board to ensure that:
The ‘D’ shape on the transistors match the board marking.
Resistor R3 has yellow, purple, black bands on it.
The ‘D’ shape on the LED matches the board marking.
The white band / ‘-’ signs on the capacitor are nearest R2 / R3.
The red wire on the battery connector goes to the ‘+’ terminal on the power terminals and the black wire
goes to the ‘–’ terminal.
Easy Build Timer Essentials
www.kitronik.co.uk/2111
Testing the PCB
Turn the potentiometers to minimum (as marked on the PCB – fully anti-clockwise). Then insert the batteries. The
LED should:
Be green for 1 second.
Then turn red.
When the button is pressed and released the same green, then red, pattern should occur.
You can now set the timer to the required period by adjusting R4.
If your timer doesn’t work as described, use the ‘Checking Your Timer PCB’ information above.
Easy Build Timer Essentials
www.kitronik.co.uk/2111
Adding an On / Off Switch
If you wish to add a power switch, don’t solder both ends of the battery clip directly into the board, instead:
Solder one end of the battery clip to the PCB, either black to ‘-‘ or red to ‘+’.
Solder the other end of the battery clip to the on / off switch.
Using a piece of wire, solder the remaining terminal on the on / off switch to the remaining
power connection on the PCB.
Easy Build Timer Essentials
www.kitronik.co.uk/2111
Start Fault finding flow chart
Fault Finding Power the board up
Check
The batteries are good and in the right
Does the way around
No
LED light The power clip is connected the right way
at all? around and soldered correctly
The pins on LED1 for dry joints or shorts
R3 for dry joints
Yes
No - its orange, Check
then dim red Does the No - Its red Q1 for shorts
LED start Q2 for dry joints or shorts
green? R2 for dry joints
LED1 is in the right way around
There is short Yes
on Q3
No - its
No - it goes off Does it
always green
turn red after
1 second?
Check
Q3 for dry joints Yes Always Starts bright,
LED1 for a short dim How bright then goes dim
is the green?
Yes Is the
LED dim? Check
Q3 for dry joints
Make sure R2 LED1 for a dry
Make sure R1 and and R3 are in joint on the pin
No
R3 are in the right the right place nearest the flat
place
Always
Does the
No bright
timer work when
the switch is
Check
pressed?
Q1 for dry joints or shorts
Q2 for shorts
Q3 for shorts
Yes
R1 for dry joints
There is a dry
R4 for dry joints
joint on SW1 Stop C1 for shorts
Easy Build Timer Essentials
www.kitronik.co.uk/2111
Designing the Enclosure
When you design the enclosure, you will need to consider:
The size of the PCB (below left).
Where the switch and LED are located on the PCB.
Access to the batteries to allow them to be changed (below right).
These technical drawings of all of these items are illustrated on this page, which should help you design your
enclosure.
All dimensions are in mm.
16
57
26
Mounting the PCB to the
enclosure
The drawing to the left
shows how a hex spacer
can be used with two bolts
to fix the PCB to the
enclosure.
Your PCB has four
mounting holes designed to
take M3 bolts.
Easy Build Timer Essentials
www.kitronik.co.uk/2111
How the Timer Works
When the power is connected to the circuit, capacitor C1 will start to ®ll. As this ®lls with charge the voltage across it
gets bigger. The variable resistor R4 controls the speed at which the capacitor ®lls.
The three transistors in this circuit are PNP transistors. These allow current to ¯ow from the emitter to the collector,
when there is 0.7 volts between the emitter and the base. As capacitor C1 charges, the voltage across it and also
across the emitter base of Q1 increases, when this reaches 0.7 volts the transistor turns on. At this point Q2 turns off
and Q3 turns on and the LED changes from green to red.
The gain of a transistor (called Hfe) is about 200. This means that the amount of current that can ¯ow through the
emitter collector is 200 times bigger than the current that ¯ows into the base. In this circuit, to get a long delay, the
variable resistor can be as big a 1 M or 1,000,000 . This means that the amount of current ¯owing into Q1 is very
small. R2 has been chosen so that the gain of Q1 is 100 times. Since the current ¯owing into the base of Q2 is 100
times bigger than the current ¯owing into the base of Q1, it is able to turn the LED on. Q3 is connected so that as Q2
turns on, it turns off, such that only the red or the green LED is on at any one time.
R3 is used to limit the amount of current ¯owing into the LED, this determines how bright the LED is. Finally when
the button is pressed to reset the timer, the capacitor C1 discharges through the button. As soon as this is released,
C1 starts to charge again. R1 is included in case the variable resistor is set to zero. As without it, when the switch is
pressed, lots of current would ¯ow from the battery into the switch. This very high current ¯ow would cause the
switch, interconnecting wire and battery, to become damaged.
Online Information
Two sets of information can be downloaded from the product page where the kit can also be reordered from. The
‘Essential Information’ contains all of the information that you need to get started with the kit and the ‘Teaching
Resources’ contains more information on soldering, components used in the kit, educational schemes of work and so
on and also includes the essentials. Download from:
www.kitronik.co.uk/2111
This kit is designed and manufactured in the UK by Kitronik
Every effort has been made to ensure that these notes are correct, however Kitronik accept no responsibility for
issues arising from errors / omissions in the notes.
Kitronik Ltd - Any unauthorised copying / duplication of this booklet or part thereof for purposes except for use
with Kitronik project kits is not allowed without Kitronik’s prior consent.
