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We create circuits that are both beautiful and functional
 

MOSTAP

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MOSTAP

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A touch sensitive
blast from the past

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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. MOSTAP is a digital version follow-up to Boldport Club's Project #5, The TAP.

In the second issue of Elektor magazine in English, February 1975, MOSTAP appeared as an improved — digital vs analogue — version of The TAP. We've re-created it for the enjoyment of those who may appreciate the elegance of the design today.

Schematic. PDF

Assembly and usage

The MOSTAP has five 'touch' buttons A through E — they work by either shorting the button with ground through skin conductivity, or through 'detecting' the mains hum through our body — only one active at any one time. A reset (X) button turns off the active button.

The project includes the following components

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Follow the schematic to assemble the project. The solid lines across pads indicate a wire jumper — use clippings of resistor legs for those. Shaded components in the schematic, and dashed lines do not need to be populated unless you intend on chaining multiple MOSTAPs, as described in the original Elektor article.

Make sure that the solder flows into the hole to make a good contact. If needed, use alcohol to clean up the pads before soldering.

Each 'button' has two outputs, indicated as N or N' (A, A', B, B', etc.) The N output comes directly from the NAND-gate IC and can only drive less than 1mA of current per pin. This is normally not enough for driving a load like an LED, and drawing excessive amount of current from the pin can damage the device. For driving loads like LEDs, use N', which is a MOSFET controlled by the N output.

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Further information

MOSTAP 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 design files using our own PCB design open source software, PCBmodE.

The circuit boards were manufactured by Eurocircuits.

MOSTAP was Project #17 of the Boldport Club. If you'd like to purchase a kit, become a member and add one to your order through the shop.

Finally, community contributions for this project are on our community site.