Detecting whether a device is currently running

Hi all,

I have a negative scanner where I have to manually forward the negative holder each time a frame is done.
I'm thinking of using a Teensy and stepper motor to forward the negative holder after a scan is done and then let the computer scan the next frame using a keyboard shortcut.

I'm currently thinking of ways to detect whether the scanner is running using an Arduino/Teensy. Unfortunately, the scanner (A Plustek 8100) does not have an indicator light that blinks when done scanning or something. It's connected using a USB cable to the computer and uses its own 12V power supply.

The options I was thinking about:
-Put a piezo on the scanner to measure vibration when the scanner is running, might be susceptible to playing music or other vibrations.
-Interupting the 12V DC power supply and measuring a drop in voltage when the scanner is running. Could I do this directly using a voltage divider and ADC on Teensy?
-Maybe some kind of circuit where the Arduino is able to read the signals over USB between scanner and computer without interupting there communication?

Curious about your suggestions!

What happens if you try to move the slide drawer while it is scanning? Maybe it locks it and it cannot easily be moved?

Can you just allow a certain (generous) amount of time for a scan?

...R

Hi Robin,

thanks for thinking along. The scanner does not clamp the negative holder while scanning or something.
Because the scanning takes quite some time and is a bit dependent on the type of scan, i thought it would be nice to have a feedback loop with the controller so it works reliably and efficient.

I just came across a ACS712 5A current sensing module. I think putting this between the poweradapter and scanner is nice because I can sense the current consumption over time. The circuit that is sensed and the circuit connected to the Arduino are isolated so that could work nicely.

Any experience/thoughts on this approach?