Touch sensing AVR placement on PCB?

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I would like to integrate two touch sensors (implemented using Qtouch lib.) to a project. The PCB that will host these buttons is a small stripe that will be installed a few cm away from the main PCB and will be connected using a few wires. Is it preferred to install the AVR itself on this small strip or is it possible to install it on the main PCB and have the touch sensing PCB connected using only a couple of wires?

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Somewhere there is an application note on touch sensor design for AVRs.

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slow_rider wrote:
two touch sensors
slow_rider wrote:
using a few wires

For two sensors I count two wires.

IIRC the R/C network must be close to the micro pin but the sensor pad can live on the end of a bit of wire. Mine did and worked well.

 

I did bodge this up first using self-adhesive aluminium tape. I can't see why you can't do something similar. It should take you only a few hours to hack something together as a test, don't folks do this anymore ? For me, that's where the fun lies in engineering.

 

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N.Winterbottom wrote:

slow_rider wrote:

I did bodge this up first using self-adhesive aluminium tape. I can't see why you can't do something similar. It should take you only a few hours to hack something together as a test, don't folks do this anymore ? For me, that's where the fun lies in engineering.

 

I intend to do that (using the same method BTW, I have some copper tape for this purpose), however before going at it, I would like to know that I'm not wasting my time. The app notes I've found say device should be close and that long wires will introduce EMF issues which is obvious, however what is long? 2cm? 4cm?

 

http://ww1.microchip.com/downloads/en/appnotes/atmel-42094-qtouch-schematic-and-layout-checklist_applicationnote_at02259.pdf

http://ww1.microchip.com/downloads/en/AppNotes/doc10752.pdf

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Since the touch points are a separate board you might want to save yourself the headache and look at the pre made touch stuff that Digikey offers. They don't cost much and all the hard work is done already.

Jim

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Last Edited: Sat. Feb 23, 2019 - 05:41 PM