- Why does connecting an external power supply cause the capacitive sensor to output erratic values?
- How can the 'No Touch Value' be stabilized, when connected to an external power supply?
I am creating a capacitive sensor on Arduino. A 10M ohm resistor sits across digital pin 4 (Send) and 2 (Receive). The conductive thread on a piece of cloth is my sensor, which is elevated off the table using a piece of plastic. I am using the Capacitive Sensing Library by Paul Badger.
What I understand
The laptop, which is connected via USB to the arduino, is part of the capacitive sensor. Touching the laptop = Touching the conductive thread
When replaced by aluminum foil as sensor, it yields the same erratic values.
Tests using different power supply
- Power supply using USB on laptop
Stable: 'No Touch Value' ranges from 0 - 35. 'Touch Value' is around 3000.
- Power supply using USB on laptop, which is charging on a power adaptor
Unstable: 'No Touch Value' ranges from 0 - 3000. 'Touch Value' is around 180000.
- Power supply to arduino using 9VDC Switch Power Adaptor, and connected using USB on laptop
Unstable: 'No Touch Value' ranges from 0 - 2200. 'Touch Value' is around 160000.
Thank you so much for your advice and time. I appreciate it.