[Taken from : https://www.youtube.com/watch?v=3KQd9F0P6PI&t=283s]

I watched this tutorial here (Explanation is from the time stamp 01:58 onwards): https://www.youtube.com/watch?v=3KQd9F0P6PI&t=283s

and I'm having trouble understanding the concept. I get the first part where when you aren't touching SW1 and the S1 is ON, the capacitor C0 is charged up. Once S1 is OFF, capacitor C0 discharges.

Not sure if I am understanding the portion when you touch the sensor correctly. My understanding: When you touch the sensor, your hand is charged (finger capacitance?) and therefore, when S1 is OFF, it takes a longer time to discharge since both your hand and the capacitor is discharging. Therefore, resulting in the micro-controller picking up the longer discharge as a touch

Many thanks in advance for any advice!


1 Answer 1


There are a few ways capacitance switches work, and that schematic is not helpful in explaining which mode is used:

  1. A conductive object (your body), even suspended in free space, has a certain amount of capacitance, i.e., ability to store charge on its surface. Touching, or even approaching, the sensor (poorly labeled "SW1", as it is not a switch), can change the voltage at that point by acting as a capacitive voltage divider. That change in voltage can be used to activate a switch.

  2. Body capacitance can be used to change the frequency of a tuned circuit, in less common use, today. That change in frequency can be used to activate a switch. This change in tuning, using an inductor, is also the basis for a type of metal detector.

  3. The human body is almost certainly at a different potential from that of the sensor. As a charged object approaches a conductor, it can induce a voltage in the conductor, and that pulse signal can close a switch. A sensitive gate SCR can be triggered with less than 1 µA, so just touching the gate lead an turn it on.


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