Electronic – Sensor to detect toilet occupancy


I'm thinking of hacking up something simple to check toilet occupancy in an office. Ideally, the system should be unobtrusive and out of the way.

I know you can use a PIR sensor to track moving objects (What sensor to choose to track human presence indoors?) – however, if somebody is sitting still on a cubicle, that will probably not register since they're stationary.

Apparently parking spot sensors use both IR and magnetic fields to detect cars (http://www.nedap.com/business-units/identification-systems/parking-detection-makes-sense/). Obviously the second part of that won't work on people.

I know you can get those IR-based sensors that bounce a beam off a reflector, however, I'm hoping to be able to mount just one sensor on the ceiling, if possible.

Is there another type of IR or ultra-sound sensors that might work here?

Has anybody got any particular parts or approaches they could suggest? Any caveats I should be aware of for this use case?

Best Answer

The automatic flush systems used at airports, movie theaters, and restaurants all use active IR technology, not PIR. Active IR uses an IR transmitter and an IR receiver. There is one sensor per toilet.

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They are located behind the toilet seat (or on the top of a urinal) and bathe the immediate area with IR light. When a person enters this field, the IR bounces back to the IR receiver and after a few seconds "arms" the unit. When the person leaves, after a couple of seconds the control unit flushes the toilet or urinal.

Commercial units cost hundreds of dollars, but at least at one time you could pick up a complete unit for a home toilet here, supposedly for $24 (I realize you don't need the flusher part, just the sensor).

There are quite a few videos on this subject on YouTube (search for "automatic toilet flush"), including ones centered around the ubiquitous Arduino.