|When this alarm is activated - the siren will sound for up to 20-minutes. Then it will switch off - and remain off. It will not sound a second time.|
How A Cmos 4001 Monostable Works
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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 25 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 .
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.
Actual Size Of Pattern
Next - make and fit the Fifteen Wire Links. For the 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.
The next stage is to fit the six diodes, the 5 fixed resistors - and the 3 presets. To fit the presets you may need to enlarge the holes slightly. Pay particular attention to the orientation of the diodes. Both the resistors and diodes are drawn lying flat on the board. However, those connected between close or adjacent tracks are mounted standing upright. See the Photo Of The Prototype.
Fit the remaining components - the five capacitors - the two transistors - the IC socket - and the relay. The PNP transistor - BC557 - is the one with its emitter arrow coloured red. Pay particular attention to the orientation of the electrolytic capacitors. They generally have a stripe down the side next to the Negative terminal. Note that the two 22uF capacitors are mounted with their negative terminals facing the top of the board. See the Photo Of The Prototype.
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 6 solder bridges.
Finish off by inserting the Cmos 4001 into the socket. Pin 1 of the IC should be in the top left-hand corner. Check that all 14 pins have entered the socket. Sometimes - instead of entering the socket - a pin will curl up under the IC.
You're Now Ready To Test Your Circuit
How To Test The Finished Alarm