Sometimes the projects of an electronics hobbyist actually find very practical and even by their own family well recognized applications :
My dear wife asked me to provide the  many LED spots at the workplace under the kitchen wall cabinets with a "better" switch. You (and me? :-) should also be able to switch the light "good and easy" even during baking and cooking with floury or sticky fingers.

Alexa and Siri have a kitchen ban with us. This quickly gave rise to the idea of building a relay-based switch that should have "only" a touch sensor running along the entire edge of the cabinet in the form of a thin wire.

In the large box with sensors and actuators for the microcontroller world, I found a suitable 5V relay with  250V/16A contacts and also a TTP223 based touch sensor board.

In contrast to all current trends: It doesn't always have to be the Arduino or ESP32 microcontroller that meaningfully connects such peripheral components, as my schematic circuit shows.
However, I still had to invest a few thoughts and a bit of time in the design and test of the sensor. The touch sensor chip TTP223 works with a  fingertip sized sensor plate whose capacitance against ground affects an internal 1MHz-oscillator. However, the sensor area - respectively its capacitance value - must not become too large.
Instead of the old sensor plate, I then experimented very successfully with sensor wires of different lengths, including a variable telescopic antenna.

My short over all  result: Thin insulated wires brought  the best results in my kitchen environment.
Finally, a two-meter-long thin insulated wire (0.5mm) well optically hidden along the entire edge of the kitchen cabinet's down side did perfectly fulfill my wife's wish, which then earned me a very nice compliment :-)


I changed the original application circuit of the TTP223 at Pin6. As this pin is connected to Vdd now, output Pin1 goes into toggle mode. Every touch of the wire now turns the  relay state and holds it then. Pin4 remains on Vss, which ensures that the relay remains switched off initially when the operating voltage is applied.

For experimenting with your own sensor plates or wires, you should know that the TTP223 dynamically adapts very well to changed capacitance values of the sensor at startup and also during operation. With an additional capacitor of a maximum of 50pF between Pin3 and Vss/ground , the sensitivity of the circuit can also be reduced in a targeted manner.

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After laboriously rebuilt my old blue touch sensor board, the long-awaited ordered 10 pieces of red TTP223 mini sensor boards arrived for 6€. These are even smaller and  are even easier to customize as described above.  The additional sensor wire can be soldered  directly on the "touch" plate. The board is so small that it could also be mounted separately from the relay board directly next to  the sensor wire. A uncritical dimensioned even up to some meters long and thin three-pole  cable then connects the two boards.

Some more detailed descriptions are  collected at https://peterneufeld.wordpress.com/2021/11/19/the-gladly-touchable-electric-wire/