Detecting when a vending machine is triggered

Hello Arduino friends,

I'm trying to make the vending machines in the office a bit more interesting and fun and would like to have some sounds and or lights triggered when someone uses them.

Preferred approaches would be those which are not invasive to the machine, so the sensing part would be easily(ish) transferrable to a new machine in case it gets switched out, and to generally avoid being a pain to the people who refill and repair them :slight_smile:

Also it would be best if it would work on all types of machines (coffee making, snacks and drinks dispensing…)

So far I’ve come up with these:

  • voice recognition to detect the sound the machines make (but not other ambient sounds)

  • power detection on the AC plug to detect when the machine is consuming electricity

  • ultrasonic or time-of-flight sensors that would detect when something is moving inside the machine (this may be too invasive)

  • metal detector on the coin input? I could 3D print a metal sensor holder to be fixed to the front of the coin slot (this sounds really nice since inserting a coin is the first point of interaction with the machine and is possibly the earliest way of detection? *Though it won't work for paying with cash/card...)

Which of these sound the most feasible and how to best implement them?

Do you have any other ideas?

Thanks to anyone for playing :slight_smile:

if the machine is refrigerated you might have a hard time noticing the delta of small motors moving - worth trying

another idea: PIR to detect someone in front of the machine? (might get a lot of false positive)

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I think an IR proximity detector to sense some motion inside the window or dispensing area of the machine. Perhaps attach the sensor to the frame with a magnet. The sketch could calibrate the sensor on startup and alert on any significant changes.

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