The cover of the first Elektor English edition, December 1974

A revival of a forty
year old kit

The board comes as a kit from the Boldport Club

The solder- component-side symbols mark when the components go.

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 circuit

The functionality of the circuit is comprehensively and beautifully explained in the original article. Here it is as a PDF, and it's really worth reading. Here is the schematics I re-created for the board.

We haven’t made any changes to the circuit, and remarkably all of the same components are still available today, including the original 7400 IC!


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.

Here are the components included in the kit:

The board's schematics (note difference values of C1 and C2 from original to reflect what's in the kits)

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.

Further information

The TAP is an open source design, as is most of our work. You can find the design files for the hardware and packaging at our GitHub repository. You can edit the files using our own source software, PCBmodE.

The TAP project was Project #5 of the Boldport Club. If you'd like to purchase a kit, become a member and add one to your order through the shop.

The board was lovingly manufactured by European Circuits in Scotland.

A full gallery of the kit is here.