This simple circuit will energize a relay at regular intervals. Both the length of time the relay remains energized - and the length of the intervals in between - are independently adjustable.
Learn More About How An Astable Oscillator Works
Click here if you're new to constructing stripboard projects.
The prototype of the timer was built using only the Stripboard Layout as a guide. So - if you reproduce the layout - you will have a working timer. Details of how to Test Your Finished Circuit Board are also provided.
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 17 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. 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. Make sure that the copper strip 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.
Next make and fit the Six Wire Links - the two presets - and three fixed resistors. 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.
Then fit the three diodes and the transistor. Pay particular attention to the orientation of the diodes. See the Photograph Of The Prototype. Note that D2 is facing downwards. All the diodes are shown lying flat on the board - but D3 is actually mounted standing upright.
Next, fit the capacitors - the relay - and the IC socket. If you are using a non-polarised capacitor connect it across pins 3 & 6 of the IC. If you are using two regular capacitors - pay particular attention to the orientation of each.
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 5 solder bridges.
Finish off by inserting the Cmos IC 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 Are Now Ready To Test Your Finished Circuit Board.
Click Here For A Photograph Of The Prototype.