Potentiometer with switch wiring question. Not reading correctly

Question

I have a potentiometer with switch, that seems to be working a little wonky (Keep in mind I have tried this with a few different pots and they all behave the same way which leads me to believe I am wiring them wrong).

I can easily hookup the potentiometer and it's three terminals on the side, 1 being ground, 2 being output, 3 being input power. I can monitor it's value on a serial port with Arduino. However when I try and test the switch, which are two terminals on the bottom of the pot. I get an on signal when the pot is on, but when it is clicked off I get a random on/off signal. As in it reads that it is sort of on but never truly reads off.

Right now I am simply giving it 5v from the Arduino to both the switch and the third terminal. Should I be giving the switch power via a capacitor? Not sure, have not tried that yet but that may smooth out my readings.

Any suggestions?

Answer 1

From your description of switch wiring, it sounds like you have one of the switch leads attached to +5 V and the other switch lead to an input.

As noted in comments and answers to "Why all unset pins of my Arduino Uno are outputting 2 volts?", such an input will read high when the switch is closed, and will read randomly when it is open, because an input is a high-impedance device that can accumulate charge:

... input impedance typically can be taken as 100 MΩ for design purposes. ... Each pin has a few pF (5-10?) of capacitance ... which in general is small compared to stray capacitances of attached wiring.

When stray electromagnetic fields charge the pin and stray capacitances, a small voltage develops on the pin. You could connect a 1 to 10 MΩ resistor between the pin and ground, to avoid the [voltage] you are seeing.

The easy fix for the problem is to attach one switch-lead to ground, one to an input pin, and initialize the pin with INPUT_PULLUP pinmode instead of just INPUT.

• Chris James Champeau: Perfect, that makes sense, I now remember this small detail when learning Arduino a long time ago