So I have a (possibly) unique project here. What I would like to be able to do is automate the flushing of a toilet, once it has been used.
The reason for this is because I manage a function centre which has several urinals. There is a 'uric acid' sensor in each of these, attached to a flushing relay & solenoid, so that when the uric acid sensor detects a certain level of uric acid, it will flush the toilet.
Needless to say, they have stopped working, and each uric acid sensor costs $500 or so, and, as fate would have it, one of the relays has also stopped working - a cost of $489 for this. So, for the sake of saving $1500, I figured there must be a good Arduino setup I could take advantage of.
I have already purchased some waterproof ultrasonic sensors (http://www.ebay.com.au/itm/Ultrasonic-Module-Distance-Measuring-Transducer-Sensor-Waterproof-DC-For-Arduino/182272591168?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649), but the beam is too broad to be useful - the toilets are too close to have enough separation in beams.
Ideally, I would place the sensor (whatever that turns out to be), above the person as they stand there to do their thing. The ceiling is around 2.4m so when someone stands, there is a distance of around 500mm - 700mm between the top of their head and the ceiling. A laser/photo-resistor is not an option as I only have limited install options - mainly directly overhead. Also, I don't want any visible light as when there is a function on, there are drunk people and they tend to be attracted to bright little dots and want to mess with them - or at least their source.
If anyone knows how I might solve this problem, I would be very happy!
I have considered:
Infrared laser diode - but don't know how to apply this, I assume a reflector/receiver is necessary.
IR Temp Sensor - no idea on spread of detection
Laser Sensor/Detector - this might be the best option, though I dont know for sure.