I have hooked the pin v5 of an Arduino Nano 33 BLE to the A0 pin and measured the value by doing Serial.println(analogRead(A0));. I would expect to see 1023 however instead I see the value oscillating around 810.

Any ideas why I am not getting 1023?

P.S.: I am powering the Arduino board through the USB connector.

  • 1
    You should probably stop doing that until you have an answer.
    – timemage
    Commented Jul 4, 2021 at 16:24
  • use a voltmeter
    – jsotola
    Commented Jul 4, 2021 at 16:48
  • it is not lower power ... it is lower voltage ... the two are not the same thing
    – jsotola
    Commented Jul 4, 2021 at 16:50
  • 1
    I hope you didn't solder the 5 V pin pads on the bottom side of the board. the 5 V pins is not connected to not make 5 V circuits just like you did. because the input pins on this board are for 3.3 V max. arduino.cc/en/Guide/NANO33BLE#please-read
    – Juraj
    Commented Jul 4, 2021 at 17:02
  • @Juraj I have soldered the 5v pin, because my sensors both require 5v. I have a Beetle Bluno BLE board that outputs 5v, I don't really understand the limitation. How am I supposed to power the sensors, with an extra external 5v power source?
    – human
    Commented Jul 4, 2021 at 17:09

1 Answer 1


Well, I thought by now someone else would have answered it. But, I'll try. I'm not familiar with this chip and board, so what I can tell you is pretty limited.

In short, you have a 3.3V micro-controller and generally speaking you don't hook 5V signals to them. There are some 3.3V parts that have "5V tolerant" inputs, but that only makes sense for digital inputs so far as I know.

Barring anything unpleasant happening, the behaviour I would expect to see with hooking 5V to the input of a 3.3V ADC is that it would clip at the high end value. So yeah, for 10-bit resolution, which appears to be the default for the Nano 33 BLE and with VDD as the reference, which also appears to be the default, I would expect to see a value at or near 1023. Up until the point that you fry something that is.

I don't know why you're seeing lower values, but since you seem to be operating it out of specifications, I'm not sure that really matters why. If you want to measure 5V with your 3.3V max ADC, you should involve a voltage divider.

  • the 5 V pin is not connected from factory on this board
    – Juraj
    Commented Jul 4, 2021 at 17:08
  • Again, I don't know what you're talking about. If you have an answer, post it as an answer.
    – timemage
    Commented Jul 4, 2021 at 17:09
  • 1
    – hcheung
    Commented Jul 5, 2021 at 1:11
  • It's nice that they have an official warning about it. The O.P. seems to remain unconvinced, for what reason I don't know.
    – timemage
    Commented Jul 5, 2021 at 1:39

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