Free Details Of How To Build A Simple Keypad Tamper-Alarm - Using Cheap Off-the-Shelf Components.
COMMENTS Homer SUGGESTIONS

Keypad Tamper-Alarm - Support Material

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Circuit Description


Click Here For A Photograph Of The Prototype.

Circuit Diagram For 
A Keypad Tamper-Alarm



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RS Components
Uk & Ireland
Maplin


Construction

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The terminals are a good set of reference points. To fit them, you may need to enlarge the holes slightly. Then turn the board over and use a felt-tip pen to mark the 18 places where the tracks are to be cut. Before you cut the tracks, use the "actual size" drawing to Check That The Pattern is Correctly Marked .

Actual Size Of Pattern

Pattern for Cutting
The Tracks on the
Underside of the Board
ACTUAL SIZE


When you're satisfied that the pattern is right - cut the tracks. Make sure that the copper is cut all the way through. Sometimes a small strand of copper remains at the side of the cut and this will cause malfunction. Use a magnifying glass - and backlight the board. It only takes the smallest strand of copper to cause a problem. If you don't have the proper track-cutting tool - then a 6 to 8mm drill-bit will do. Just use the drill-bit as a hand tool - there's no need for a drilling machine.

Keypad Tamper-Alarm
Construction Guide


Next make and fit the Four Wire Links. I used bare copper wire on the component side of the board. Telephone cable is suitable - the single stranded variety used indoors to wire telephone sockets. Stretching the core slightly will straighten it - and also allow the insulation to slip off.

Then fit the 5 resistors. The resistors are all shown lying flat on the board. However, those connected between close or adjacent tracks are mounted standing upright. See The Photograph Of The Prototype.

Next - fit the transistor and the four diodes. Pay particular attention to the orientation of the diodes. Note that D1 is mounted with its kathode (the side with the bar) pointing downwards. See The Photograph Of The Prototype.

Keypad Tamper-Alarm
Construction Guide


Fit the three capacitors and the IC Socket. Pay particular attention to the orientation of the electrolytic capacitor. Note that electrolytic capacitors generally have a light coloured stripe down the side next to the negative terminal. C3 is mounted with its positive terminal facing downwards. See The Photograph Of The Prototype.

Next - turn the board over and examine the underside carefully - to make sure that there are no unwanted solder bridges or other connections between the tracks. If you backlight the board during the examination - it makes potential problem areas easier to spot. When you're satisfied that everything is in order - add the 4 solder bridges.

Finish off by inserting the Cmos 4017 into the socket. Pin 1 of the IC should be in the top left-hand corner. Check that all 16 pins have entered the socket. Sometimes - instead of entering the socket - a pin will curl up under the IC.


Test Your Finished Circuit Board

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