Touch switch electronic circuit based on a Schmitt trigger
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This touch switch electronic circuit is based on a Schmitt trigger with latching, built IC1a, IC1b and R3. IC1b's output signal comes back to IC1a input through R3, resulting in maintaining stable condition of both gates. While the circuit is at rest, the anode of D1 is at "0" and the cathode of D2 is at level "1" retain their status.
When contact is shorted by finger touch, the voltage drop across R8 increases. This increase is translated into a short pulse of R1-C1. This pulse transmit through D1 a “ 1” at input of ICla. IC1b's output and output will also go to "1".
When C2 is charged circuit is ready to change the status of the next stimulus appeared on R1. This momentum will make it output IC1a become "0", in which the output of IC1b becomes “ 0 “ C2 voltage decreases. Output is again,, 0 "circuit again is at the point from which it started.