Electronic – arduino – Voltage divider/reduction with no current draw

arduinoledvoltage dividervoltage measurement

I am trying to measure the voltage on an LED in an open circuit (awfully shown below) using an arduino, however the voltages are too high for its inputs.

I have tried:

  1. Using a voltage divider (~10K total resistance), however current flows and the LED lights up (which I do not want)
  2. Bumping up the total resistance of the divider to ~10M, the LED glows extremely dimly (which is fine), but now the arduino doesn't read the voltage correctly (due to noise or something?)

So now, I have decided to use some Zener diodes to drop the voltage before connecting with the arduino, is this (theoretically) going to work? Or is there some simpler/smarter way around this?

Also stumbled on this: Measure voltage with no current, but it seems a bit more complicated than using the diodes.

awful diagram

Any input is greatly appreciated.
Many thanks

Update: Thanks everyone for all the help, ended up using the pull-up as it was the simplest

Best Answer

Perhaps I am missing something here, but from your comments you seem to only need to know when the LED is on, or to put it another way, when the switch is closed.

You can do that with a simple diode and a pull-up.

schematic

simulate this circuit – Schematic created using CircuitLab

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