6

Is it possible to make a capsense sensor that works through a sheet of glass? I have a working capsense sensor on one of these PSoC development boards:

PSoC Capsense

The buttons work fine, but when I put a sheet of glass on top, they don't work. Do I need to bond the buttons to the back of the glass to make this work? If so, do I need to use a particular type of glue?

Rocketmagnet
  • 26,933
  • 17
  • 92
  • 177
  • FYI Qprox (now Atmel) sensors on a standard PCB works perfectly behind a 1/2" tick glass panel, after a little tuning of capacitors, without glue... – Axeman Sep 12 '12 at 12:41

1 Answers1

7

Since the capacitance change will be much smaller due to the extra distance, you will need to set the sensing algorithm up accordingly for the new setup.

You can get an idea of things by displaying the sense value for pressed/not pressed on the LCD with and without the glass.
Then you can tune the thresholds, averaging, filtering, etc (e.g. a longer integration period is better for confirming the smaller change, but makes the response time slower) I imagine Cypress should have an app note on doing all this, Microchip have a few decent ones too if they don't have much (how useful depends on how the Cypress peripherals function, though they are likely to be very similar)

Oli Glaser
  • 54,990
  • 3
  • 76
  • 147
  • OK, but I shouldn't need any glue or anything ? – Rocketmagnet Sep 12 '12 at 13:30
  • As long as it's a reasonably tight fit (and not prone to variations) it should work fine without glue. Contact adhesives can be used to ensure good contact though. – Oli Glaser Sep 12 '12 at 14:22
  • Aah! Just got it working! I hadn't set it to Auto Tune, so it was just using the tuning values from the original dev board. – Rocketmagnet Sep 12 '12 at 14:31
  • Good stuff - if it has an auto tune mode then I'd imagine that will make getting things working much less hassle. Pity the Microchip ones I've used don't have that function. Might have to have a go with one of these PSoC things, they look pretty interesting. – Oli Glaser Sep 12 '12 at 14:37