Touch Switch - please explain me the circuit

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tkb5416

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Touch Switch

Hi,

I have tested on the circuit that I found from website(**broken link removed**).

It works perfectly.Can anyone explain to me the details of how the circuit works?

Thanks.
 

Re: Touch Switch

Pin 1 is held high by R3. When a current flows through R2 to ground (between the touch contacts) the logic level on pin 1 changes to low.

This makes pin 3 change state and charges C1. U1B is connected as an inverter so as C1 charges, the current through it pulls pins 5 & 6 high and makes pin 4 go low. this resets the output of U1A low again. So each time you touch the contacts you get a pulse at the output while C1 charges, the value of C1 sets the pulse length.

You should really connect a diode across R1 to protect U1B. There is a risk that when the output goes low, residual charge on C1 will take pins 5 & 6 below ground potential and cause damage.

Brian.
 

Re: Touch Switch

Thank you Brian, I appreciate it.
 

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