This ten channel touch switch circuit can be used to generate ten individual on/off outputs in response to the touching of ten respective touch pads.
Touch switches are available in all manner of sizes and shapes, primarily as temporary action or easy on/off (latched) switches.
Using only a good number of components, it is easy to build a ' ten-channel ' TAP, i.e. a ten-pole touch switch.
When among the ten sets of contacts is touched, the corresponding output will probably be taken high.
How the Circuit Works
The heart of the circuit is made by a CMOS decade counter/decoder, 4017, which can be clocked by a easy CMOS oscillator.
On the other hand when the contacts are open, the counter is inhibited, since the clock enable input is placed high.
Precisely the same is valid in case the contacts are bridged, however the corresponding output is readily high, since it's possible that the additional skin resistance will have no impact.
On the other hand, if the corresponding output is low when a set of contacts is touched, the skin resistance (which is negligibly small compared to the other resistances) forms part of a voltage divider, thereby pulling the clock enable input low.
The counter is started and increments prior to the output involved is taken high, whereupon the clock enable input is once more taken high and the count is stopped.
Capacitor C2 is included to suppress mains transients etc., whilst R4…R14 avoid the chance of a shock in case of a short between the contacts.
It ought to be emphasized that when the counter is started off, each output from this ten channel touch switch circuit consequently goes high (for a very short period) till the preferred channel is switched.
This certainly will not prove to be a difficulty with most applications, on the other hand accessibility needs to be made for this when used with flip-flops and other edge triggered devices.