I have a circuit running with capacitive Sensors, that also has an LED strip. everything works fine when using USB power from a laptop (connected to the mains) and 12v 2A adapter powering 1m LED strip.

When the power supply is split and the arduino is also powered from this supply ( using adapter port ) the capacitive sensor begins to give junk values.

What changes in a circuit that would create such a porblem? Could it be a grounding issue? How else to ground this arduino to behave as it would with a usb connection?

  • Powering using 9V battery or same 12v 2a shared connection in the Vin port produces a different set of problems, where the sensor loses its range. How are the various methods of powering the board changing the behavior so much? Jun 11, 2015 at 20:29
  • They should share the ground connection. Also, do you have any drawings? Of the working situation and where it goes wrong?
    – aaa
    Jun 12, 2015 at 7:11

2 Answers 2


I have run into problems like this before, often it can actually be that the voltage is not steady due to the LEDs sourcing current from it.

You may be able to solve the problem by adding a capacitor inline with the power input (from the +12v to GND). I would probably start with a value of around 10 μF and increase it if the interference continues.

Capacitive sensors and very sensitive to voltage fluctuations, you may even want to put a second capacitor across the VCC and Gnd of the sensor.


Some of the capacitive sensors need a seperate regulated power supply.You can look into the data sheet of the capacitive sensor.Maybe you can try with the same. I just read the datasheet of At42qt2120 cap sensor.

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