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Hey guys I need help with understanding the circuit diagram from this link: https://playground.arduino.cc/Main/CapacitiveSensor?from=Main.CapSense

As of now, this is the schematic I drew from what I understand:

https://imgur.com/YBvBupJ

I know it is wrong since they make use of 2 capacitors, but I do not know where should the other capacitor be connected to.

  • look again, they do not use any capacitors – jsotola Mar 12 '18 at 4:18
  • They mentioned adding of capacitors in the documentation and it is also shown in dotted lines. – Dominic Teo Mar 12 '18 at 4:23
  • Looks like the cross-post was removed. – Nick Gammon Mar 12 '18 at 5:15
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    Also asked at: github.com/PaulStoffregen/CapacitiveSensor/issues/27 If you're going to do that then please be considerate enough to add links to the other places you cross posted. This will let us avoid wasting time due to duplicate effort and also help others who have the same questions and find your post to discover all the relevant information. – per1234 Mar 12 '18 at 6:23
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The other capacitor shown in the article is the ambient capacitance (that is, the capacitance between the pin and the things around it). There is no actual capacitor.

What it is saying is that there is a RC circuit (the supplied resistor and the capacitance in the air) which will change the charging time of the RC circuit as the capacitance changes, when you move your hand near it.


From a comment:

and the other capacitor with a value of 20-400pF

Yes, it does say that:

Adding small capacitor (20 - 400 pF) in parallel with the body capacitance, is highly desirable too, as it stabilizes the sensed readings.

However that doesn't make any sense to me. How do you add a capacitor in parallel with your body? Do you carry one around with really long wires? And how do you hold it? I would ignore that part.

  • Based on the documentation, it mentions that 2 capacitors are used. 1 of the capacitor with a value of 100pF and the other capacitor with a value of 20-400pF. – Dominic Teo Mar 12 '18 at 5:27
  • @DominicTeo See amended answer. – Nick Gammon Mar 12 '18 at 5:36
  • So ignoring the capacitor in parallel with the body, does my circuit drawing looks correct? – Dominic Teo Mar 12 '18 at 5:38
  • Yes it looks like what the referenced web site has. – Nick Gammon Mar 12 '18 at 6:29
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This question appears to get posted every week! There is NOT 2 capacitors. The Csensed capacitor in dotted lines is the capacitance added when you touch the plate. The Cpin capacitor is suggested to stabilise the readings and is not required. So in the circuit NO capacitors are used. All you need is a high value resistor between the Send Pin and Receive Pin and put your plate on the Receive Pin.

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