AT42QT-1011 capacitive sensor questions

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adampcloth
 
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AT42QT-1011 capacitive sensor questions

Post by adampcloth »

Hi All,

I am after some help with the AT42QT-1011 capacitive touch sensor. A little history before I ask my question.

full history here: https://forum.arduino.cc/t/proximity-se ... /970815/16

TLDR: I have 24 sensor points that I want to trigger through about 1 cm of wood. The ttp-223 break outs I used with a ring of copper wire soldered to the sensor pad would trigger about 0.5cm above the wood, however due to the 'auto-calibration' 'feature' they stop triggering after 7-8 seconds. The AT42QT-1011 datasheet says this sensor will stay 'triggered' for as long as it senses something. I have bought a few to test.

My questions are:
1: touching the sensing pad on the AT42QT-1011 with my finger has mixed results. Some times it will stay triggered for as long as my finger is touching and some times it will only last about 6-15 seconds before the led switches off. I did read some thing about power maybe being the cause of this. I have tried it using a breadboard powered from a 5v adapter and from a USB connected to a PC and the results are the same. The item I'm trying to build is powered by this: https://www.amazon.co.uk/Switching-Powe ... B07Q2WQ8DS So what could be the issue here and for the final item is there a recommend PSU?

2: I am experimenting with adding an external sensing pad so it will be triggered through the wood, again with mixed results. I have some copper tape and this kind of works through the wood but some times not and then doesn't stay triggered. Any ideas on how to build a pad that works through the wood would be gratefully received.

Thank you for your help.

Adam

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adafruit_support_mike
 
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Re: AT42QT-1011 capacitive sensor questions

Post by adafruit_support_mike »

The first issue is probably pad size.

To a simple approximation, capacitive sensors detect what's in a hemisphere centered on the pad. If you want to sense through 1cm, you'll need pads larger than 1cm in diameter.

You also mentioned using rings of wire as the sensors. That's problematic for capacitive sensing because the strength of a capacitor depends on its surface area. If you aren't using foil pads, give those a try.

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