FSR sensor readings change when USB is unplugged

Other Hardware Motors, Mechanics, Power and CNC
1

Hi, I'm doing an installation with Neopixel LED strips and vibrations motors that respond according to touch, from readings from FSR sensors. The color changes gradually from cool to warm and the motors turn on when the FSRs detect pressure. I drew a schematic diagram that is attached.

Everything works well when testing and calibrating my program's response according to the sensor readings (from Serial monitor) when the Arduino is connected to both the USB and the 5V wall power supply, however when I unplug the USB the color of the lights change immediately and it doesn't respond the same way.

I suspect somehow the voltage of the circuit changes when the USB is unplugged? However shouldn't it draw power from the wall supply even with the USB plugged in?

schematic.gif
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2

Schematic shows 5V into Vin if I read it correctly?

Read here and see that Vin needs to be 6V min, 7V preferred.

And I think it chooses the USB over that, so that would be a regulated 5V already which is good, whereas 5V on Vin still gets regulated on board so it ends up too low.

3

Thanks! Somehow I missed that despite spending an hour googling.

According to Arduino Uno R3: Directly supply regulated 5V to 5V pin? - Electrical Engineering Stack Exchange, it seems that connecting my 5V supply to the 5V pin would solve the problem.

4

seeyf:
seems that connecting my 5V supply to the 5V pin would solve the problem.

Except that the same source linked above says this:

Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.