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

Hijack Alarms - Testing Your Circuit

ANOTHER VEHICLE ALARM

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First Hijack Alarm - Construction Guide Enhanced Hijack Alarm - Construction Guide

Introduction

The prototype of the Hijack 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.


Setup

You can use this procedure to test both Hijack Alarms. A resistor and an LED are all that's needed to demonstrate that the "Buzzer" output is working properly - and the same arrangement can de used to simulate the "Siren". A couple of pairs of wires will serve as the "Door" and "Reset" switches - and for the "Ignition" - you can use any small single-pole switch.


Details of How to Prepare The
Vehicle Hijack Alarm For Testing


Connect an LED - in series with a 2k2 resistor - across the "Buzzer" terminals. Do the same across the "Siren" terminals - and connect an LED to the "LED" terminals. Connect a 2k2 resistor between the positive terminal and the "Pole" terminal - and connect two LEDs from the "N/O" and "N/C" terminals to the negative terminal.

I used five different colour LEDs in the diagram because - in what follows - I want to be able to distinguish between them. But you can use whatever colours you have available.

Next, connect the "Ignition" switch between the positive terminal and the "Ignit" terminal. Move the switch to the "Off" position - and leave it there.

Connect two pairs of wires to the "Door" and "Reset" terminals. 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. You don't have to.

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.


Turn On The Power

When you turn on the supply all the LEDs - except for the white one - should be off. Turn the "Ignition" switch on. Ry2 should energize - the white LED should turn off - and the blue LED should light.

If you are testing the Enhanced Hijack Alarm - when you turn on the "Ignition" - in addition to the above - the yellow LED will flash briefly - and the red LED will light. Touch the ends of the two blue wires together momentarily - to turn off the red LED - and to reset the alarm.

To simulate the opening of a door - touch the ends of the orange wires together. The yellow LED should flash briefly - and the red LED should light and remain lit. This means that the "Buzzer" has given a short beep to warn you that the alarm has been triggered - and the red LED is providing a constant reminder that the "Siren" is about to sound.

After three minutes or so - Ry1 should energize and both the yellow and green LEDs should light and stay lit. This means that both the "Buzzer" and the "Siren" are sounding.

About one minute later - Ry2 should de-energize - the blue LED should turn off - and the white LED should light. This means that the engine has cut-out.

There is no time limit on the siren or the engine cut-out. The circuit must be reset manually. If you haven't already done so - separate the orange wires. Then touch the blue wires together briefly. The alarm should reset. That is - the red LED should turn off - Ry1 should de-energize and the yellow and green LEDs should turn off - Ry2 should energize - the white LED should turn off and the blue LED should light.

Do the test again. Start by touching the two orange wires together. You should get a short flash from the yellow LED - and the red LED should light and stay lit. Let's say that this is an accidental activation. Make sure that the orange wires are not touching - i.e. the doors are closed. Touch the two blue "reset" wires together. The red LED should turn off. This means that the alarm has been successfully reset.

Do the same again - but this time twist the two orange wires together and leave them that way. The yellow LED will flash and the red LED will light. Try touching the blue wires together. The circuit should NOT reset - because the "Door" is still open.

Wait until Ry1 energizes and the green and yellow LEDs light - then turn off the ignition. Ry2 should de-energize - the blue LED should turn off - and the white LED should light. However, the "Siren" and "Buzzer" outputs should continue - even after the ignition has been turned off. This means that - once tripped - turning off the ignition will not prevent the alarm from functioning correctly.

Wait another minute or so - then turn on the ignition again. It should have no effect on the outputs. By now the engine cut-out will have been activated - so turning on the ignition will not energize Ry2. The red, yellow, green and white LEDs should continue to light - indicating that the alarm has been tripped - the Buzzer and Siren are both sounding - and the engine has been disabled.

Untwist the orange wires and touch the ends of the blue wires together briefly. The alarm should reset. That is - the red LED should turn off - Ry1 should de-energize and the yellow and green LEDs should turn off - Ry2 should energize - the white LED should turn off and the blue LED should light.

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 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. 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. 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 provided - 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 twelve 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. Look for unwanted solder bridges. Your felt-tip markings will tell you which ones should be there - and help you identify the ones 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 relevant assembly instructions provided. 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.


First Hijack Alarm - Construction Guide Enhanced Hijack Alarm - Construction Guide

Hijack Alarms - Schematic Diagrams The Rest of Ron's Circuits Write To Ron More Free-to-Use Circuits Circuit Exchange International