Build this burglar alarm circuit yourself using veroboard and cheap off-the-shelf components. It has automatic Exit and Entry delays, a timed Bell Cut-off and a 24-hour Personal Attack/Tamper zone. Its modular design means you can add as many zones as you like.
Introduction
The prototype of the Two-Zone Module was built using only the Stripboard Layout as a guide. So - if you have faithfully reproduced that layout - you will have a working circuit.
Once you're satisfied that your layout is correct - and you have made a careful and thorough check of the underside of the board - it's time to power-up the circuit and test its operation. This is always an anxious moment. If you construct a lot of circuits - you might consider building the
Current Limiting Power Supply - or alternatively - you could add the Simple Current Limiter to your existing PSU. Both will let you set an upper limit on the amount of current supplied to your circuit - and so protect it from any serious damage.
Setup
There's no need to connect the actual trigger-switches in order to test your circuit board. You can simulate them using short lengths of flexible multi-stranded wire - such as alarm cable. Don't use single stranded wire. It's awkward to handle - and doesn't take well to being twisted and untwisted. An LED is all that's needed to demonstrate that the output is working properly.
Connect the short lengths of wire to the inputs. Strip the insulation from the ends of the wires and twist them together to simulate the Zones 1 and 2 normally-closed Loops. Note that the two wires connected to the Zone 2 normally-open input are not twisted together.
Connect an LED between the "pin 8" output and the negative line. There is no need to use a series resistor. The job of limiting the output current is done by RZ4. I used a Yellow LED in the diagram because - in what follows - I wanted to be able to distinguish between it and the other LEDs on the circuit board. You can use whatever colour you have available.
Next, connect the on/off switch - SW1. Then place the switch in the "Off" position - and leave it there.
Finally, connect the 12-volts DC to the input terminals. Pay particular attention to the polarity of the supply. Note that the positive connection goes to the top terminal.
Turn On The Power
The two green LEDs should be lighting - and the two red LED should be off. While SW1 in the "Off" position - we want the green LEDs to react to inputs from the trigger-switches - but we don't want the red LEDs to record the inputs as alarm activations. Begin by testing Zone 1.
Untwist the wires connected to the Zone 1 input. Then touch them together a few times - to open and close the loop. As you do so - the green Zone 1 LED should turn off and on. But the red fault LED should not light. When you're satisfied that it's working properly - twist the two wires back together and move on to Zone 2.
Begin with the normally-open input. Touch the ends of the two wires together a few times. As you do so - the green Zone 2 LED should turn off and on. But - again - the red fault LED should not light. When you're satisfied that it's working properly - separate the two wires from one another and move on to the normally-closed input.
Untwist the wires connected to the Zone 2 normally-closed input. Then touch them together a few times - to open and close the loop. As you do so - the green Zone 2 LED should turn off and on. But again the red Zone 2 LED should not light. When you're satisfied that it's working properly - twist the two wires back together and move SW1 to the "Set" position.
Now that the alarm is set - we want the inputs to produce an output at the "Pin 8" terminal. We also want the two red LEDs to provide a visual record of the activation - and to continue to do so - even after SW1 is subsequently moved to the "Off" position.
Start by touching the Zone 2 normally-open wires together. Both the yellow LED and the Zone 2 red LED should light. Separate the wires again. The yellow LED should turn off - but the red LED should remain lit. Touch the wires together a few more times. Each time - the yellow LED should turn on and off - but the red LED should remain lit. This means that the Zone will reset - and continue to operate - even with the red LED lit.
Separate the two wires - and move SW1 to the "Off" position. The red LED should remain lit - to indicate that Zone 2 has caused an alarm activation. When you're ready - press the reset button - and the red LED should turn off.
Next, check the normally-closed loops of both Zones 1 and 2. Begin by moving SW1 to the "Set" position. Then open the normally-closed loop of Zone 1. Both the yellow LED and the Zone 1 red LED should light. Touch the wires together again. The yellow LED should turn off - but the red LED should remain lit. Open and close the loop a few more times. The yellow LED should turn on and off. When you're ready - twist the two wires together again - and carry out the same test on Zone 2.
Open the normally-closed loop of Zone 2. Both the yellow LED and the Zone 2 red LED should light. Touch the wires together again. The yellow LED should turn off - but the red LED should remain lit. Open and close the loop a few more times. The yellow LED should turn on and off - but the red LED should remain lit.
Next, twist the two wires together - and move SW1 to the "Off" position. Now - even though the alarm is switched off - the red LEDs should remain lit - to record the fact that both Zones 1 and 2 have caused an activation. When you're ready - press the reset button - and the two red LEDs should turn off.
If You Find a Problem
If - in the course of the test - you find that something is not working properly - then a careful inspection of the relevant area of the circuit board should turn up the cause of the problem. Where you've cut the board to size - look for small loose strands of copper left behind by the saw. Check the board for short-circuits caused by component leads touching each other. If an LED is not lighting - check that it's connected the right way round. It can also happen that the stripboard itself is faulty. I have seen cases where the copper tracks have not been completely severed from one another during manufacture.
If you've built your circuit using the specified components - and you've followed the step-by-step construction guide described on the Two Zone Module Support Page - then the chances are that any bug will be caused by something minor - a component connected the wrong way round - a missing or unwanted solder bridge - an incomplete cut in the track etc.
If you can't see anything obvious then adopt a systematic approach to faultfinding. Begin by double-checking that all of the cuts in the tracks have been made, that they are all - In The Right Place - and that they sever the track completely. Use a magnifying glass. It only takes the smallest strand of copper to cause a problem.
When you're satisfied that the tracks have been severed in all the right places, check that you have made - and correctly placed - all 6 solder bridges. Check especially the bridge that connects pin 14 of the IC to the positive line. Mark each bridge with a felt-tip pen - or something similar - so that it can be easily identified later.
Next - carefully examine the full length of each track. Look for unwanted solder bridges. Your felt-tip markings will tell you which ones should be there - and help you identify any that shouldn't be there.
If all else fails and you still haven't found the cause of the problem - work your way through the assembly instructions on the Support Page. Check each individual component and link - to make sure that it's present and correctly positioned.
Print out the drawings and mark off the components as you go. Pay particular attention to the orientation of the diodes and transistor. Make sure that Pin 1 of the IC is in the top left-hand corner - and that all of its pins are correctly inserted into the socket. Take your time and examine each individual component carefully.
SUGGESTIONS
