The components used in the circuit should be widely available. However, none of them are critical. So - if you can't find the specified parts - You're certain to find something that will do just as well
. And - if you prefer to make your own PCB - The Stripboard Layout Is Easily Converted
Stripboard or Veroboard is a board drilled with a matrix of 1mm holes spaced approximately 2.5 mm apart and joined in rows by copper strips. The piece used for the prototype has 24 rows with 32 holes in each - and measures about 9 cm by 6 cm (3.2" by 2.4"). The drawing shows the board with PCB mounting terminal blocks. But to save money - and/or space - the wires may be soldered to veropins - or directly to the board itself.
Click Here For A Photograph Of The Prototype.
Click here if you're new to constructing stripboard projects.
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 34 places where the tracks are to be cut. Before you cut the tracks, use the "actual size" drawing to Check 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 - 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.
Next fit the Thirteen 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 allow the insulation to slip off.
Next - fit the 16 resistors. The resistors are all 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 four transistors - the two LEDs - and the eight diodes. The PNP transistor - BC557 - is the one with its emitter arrow coloured red. Pay particular attention to the orientation of the diodes. Note that two of the diodes - D2 & D6 - are mounted with their cathodes facing the bottom of the board.
Fit the remaining components - the ten capacitors - the two IC sockets - and the relay. 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 C6 has its Positive
terminal facing down.
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. These are just small blobs of solder - used to connect two adjacent copper tracks.
Finish off by inserting the two Cmos ICs into their sockets. Pin 1 of each IC should be in the top left-hand corner. Check that every pin has entered its socket correctly. Sometimes - instead of entering the socket - a pin will curl up under the IC.
You Are Now Ready To Test Your Circuit