Build this vehicle alarm circuit yourself using veroboard and cheap off-the-shelf components.

COMMENTS SUGGESTIONS	Car Alarm - Testing Your Circuit	VEHICLE HIJACK ALARM

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Car Alarm - Support Material

Introduction

The prototype of the Car Alarm 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.

Test Setup

Details Of How To Prepare
The Car Alarm For Testing

A resistor and an LED are all that's needed to demonstrate that the Buzzer output is working properly.

The same arrangement can de used to simulate the Siren. 

A couple of pairs of wires will serve as the trigger switches. 

And Sw1 can be any small single pole two-way switch. 

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Connect an LED - in series with a 2k2 resistor - across the Buzzer terminals. 

Do the same across the Siren terminals.

Connect an LED to the LED terminals. 

I used three different colour LEDs so that - in what follows - I can distinguish between them. 

You can use whatever colours you have available.

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Next, connect the on/off switch - SW1. 

Pay particular attention to the position of the Pole. 

It doesn't matter which way round the other two connections are made. 

Move the switch to the Off position - and leave it there. 

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Connect two pairs of wires to the Door and Inst terminals. 

You really only need three wires. But - for clarity - I used two pairs.

Strip the ends of the wires - but do not allow them to touch each other. 

Again - I made the pairs different colours so that I can distinguish between them. 
     
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Finally - connect the DC supply to the input terminals. 

Pay particular attention to the polarity of the supply. 

Note that the positive connection goes to the top terminal.

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            Turn On The Power 

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All three LEDs should be off. 

Move SW1 to the set position. The red LED should light and remain lit. 

Wait for about 30 seconds. Then touch the blue [Door] wires together. 

The yellow LED should light and remain lit. 

This indicates that the alarm has triggered - and the Buzzer is sounding. 

After about 10 to 15 seconds - the relay should begin to energize and de-energize.

And the green LED should switch on and off at the rate of about once a second. 

This indicates that both the Entry delay and the Siren output are working correctly.

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If you haven't already done so - separate the two blue wires. 

About 3 minutes after you separate the wires - the yellow LED should turn off. 

And 10 to 15 seconds later - the green LED should stop flashing. 

This indicates that both the timed output and the automatic reset have functioned properly. 

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Repeat the test. This time touch the two red [Inst] wires together. 

As before - the yellow LED should light. But there should be no Entry delay. 

The green LED should start to flash immediately. 

This indicates that the Instant switch has triggered the alarm - and bypassed the Entry delay. 

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If you haven't already done so - separate the two red wires. 

About 3 minutes after you separate the wires - the yellow LED should turn off. 

And 10 to 15 seconds later - the green LED should stop flashing. 

This indicates that both the timed output and the automatic reset have functioned properly. 

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Next - test the Exit delay. 

Move SW1 briefly to the off position - then move it back to the set position.

During the first 10 to 15 seconds - you should be able to touch the ends of the blue wires together without triggering the alarm.

This indicates that the Exit delay is working properly - and you can leave the vehicle without setting off the alarm. 

Note that the delays apply only to the Door switches. 

The Instant switches will trip the alarm during both the Exit and the Entry delay. 

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When the Exit delay expires - touch the ends of the blue wires together. 

The yellow LED should light - and the Entry delay will begin. 

Wait for the Entry delay to expire and the green LED to flash. 

Then move SW1 to the off position. 

Both the yellow and the green LEDs should turn off. 

This means that the alarm can be silenced at any time - by moving SW1 to the off position. 

Repeat the tests as often as you like - until you're satisfied that your circuit is working reliably.

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.

If an LED is not lighting - check that it's connected the right way round. If you're not using the specified transistors - check the pin configuration. Even if your transistors look like BC547s and BC557s - they may still have a different pin configuration.

Check the board for short-circuits caused by component leads touching each other. 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. Where you've cut the board to size - look for small loose strands of copper left behind by the saw.

If you've built your circuit using the specified components - and you've followed the step-by-step construction guide described on the Car Alarm - 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 - and backlight the board. 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 seven solder bridges. 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. Use a magnifying glass - and backlight the board. 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. Take your time and examine each individual component carefully. Pay particular attention to the orientation of the diodes - transistors - and electrolytic capacitors.

Car Alarm - Support Material

Car Alarm Photograph	The Rest of Ron's Circuits	Write To Ron	More Free-to-Use Circuits	Circuit Exchange International

Car Alarm - Testing Your Circuit

Introduction

Test Setup

If You Find a Problem