A revival of a forty year old kit
At a time when powerful processors are so cheap and much of their functionality left unused in a typical application, it’s delightful to look back to hobbyist electronics projects from forty years ago, and admire the optimised design and the skill of those who created them.
In the first edition of Elektor magazine in English, December 1974, appeared a lovely touch-activated circuit. We've re-created it for the enjoyment of those who may appreciate the elegance of the design today.
The TAP was project #5 of the Boldport Club.
13x bipolar (BJT) single transistor NPN, Fairchild PN2222ATA
2x NAND gate 4 gate, 2 input, TI SN7400
3x Small signal diode 1V Multicomp 1N4148
1x bipolar (BJT) single transistor PNP Fairchild BC556BTA
4x 10MΩ resistor, Multicomp MCF 0.25W 10M
7x 27KΩ resistor, Multicomp MCF 0.25W 27K
3x 100KΩ resistor, Multicomp MCF 0.25W 100K
1x 1KΩ resistor, Multicomp MCF 0.25W 1K
2x 220pF capacitor, Vishay K221J15C0GF53L2
1x 47nF capacitor, Multicomp MC0805B472K500A5.08MM
2x 14-pin IC DIP socket , TE Connectivity 1-2199298-3
1x 20-contacts 2.54 mm header, Multicomp MC34739
Before you do anything, note which side the components are mounted. Look for the symbols described here for an indication.
The 'legend' — the component symbols — on the back-/solder-side of the board is meant to help you orient the components from the top. Also note that there are two wire jumpers, and these need to be bridged with a wire or a clipping from other components.
Also note that T8 is a PNP transistor, whereas the rest are NPN transistors. We suggest that you place it first so to avoid confusion.
The touch pads can be cleaned with alcohol if they oxidise.
To maintain the original look of the circuit (it was exposed copped), we've used transparent solder mask (instead of the standard green) to protect the copper. The touch pads and solder pads are exposed, and may oxidise (this is normally prevented by a 'finish', which isn't applied here); is that's the case, apply some alcohol to clean the pads up.
When assembly is complete you can connect an LED (and current limiting resistor) to the outputs. You could easily use the Cordwood Puzzle for that as it has three LEDs.