Capacitive keypad

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#1
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I bought a few different inexpensive keypads and also tried individual push buttons. For what I want they are all a bit clunky.
From initial tests it looks like a cheap capacitive keypad is viable but I'd need to play around with the circuit design a bit. I couldn't easily find anything doing searches.
If anyone has links to a working schematic it would be appreciated. TIA.

Ralph Hilton

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rhilton wrote:
I bought a few different inexpensive keypads and also tried individual push buttons. For what I want they are all a bit clunky.
From initial tests it looks like a cheap capacitive keypad is viable but I'd need to play around with the circuit design a bit. I couldn't easily find anything doing searches.
If anyone has links to a working schematic it would be appreciated. TIA.

QProx makes some very nice chips that are designed for capacitve keypads. I've used some QProx chips (QT150s) in the past and I have been very pleased with them.

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I second the nod on the QProx. I've been using them in a project and they do work very well.

A few things to watch out for though - you need a nice quiet power supply for them or you might pick up false triggers depending on how sensitive you set them up. Also, if you go for the multi-input ones (i.e. the QT320) then there is a slight difference in sensitivity between the two channels and you might want to pay attention to the datasheet on the auxiliary capacitance to equalize the responses. And lastly, in setting these guys up, an oscilloscope is handy. Not absolutely necessary, but handy.

But the end result is worth the work. You can put your circuit in plastic equipment boxes without having to machine for actual switches or a membrane keypad tail and also, end users just think it's kind of cool to be able to actuate stuff without actually having to touch something. You can go with the plastic overlay route with the switch borders drawn in and have all the durability of the overlay without the eventual cracking of membrane pads.

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