Kiley, Allie, and I met with Lilian de Greef and Edward Wang, both PhD students in the Ubiquitous Computing lab at UW, about possible sensors for tracking product levels in feminine hygiene dispensers. We began by showing them pictures of the dispenser we’d recently disassembled and they immediately offered a variety of options, which were then vetted by the group:
- Magnetic Sensor
- IR sensor
- Sonic – something from the top
- Circuit inside, resistance changes
- More material you cover, the more resistant it is
- don’t use dangerous amount of current! (what if the person servicing the dispenser is wearing a metal bracelet?)
- stretchable resistance, electrical resistance changes as it changes
- Sound sensor
- how many times was the coin operator turned
- at dispenser – switch bend (momentarily)
- momentary switches
- two magnets, one on the top, one at switch
- they will interfere with each other, so probably not a good idea
- sensor mounted at top moving toward
- magnet – not work because of cross talk (proximity between tampons and pads)
- *absolute sensor
- TDR – know what part of wire you’re pressing on
- slider – resistive material – more material more resistive
- long linear potentiometer (like a dimmer)
- multiple switches as it goes down
- could approximate # of tampons from that
- IR proximity sensors array – calibration/threshold for tampons
- covered → something there
- not covered → not there
- uses “lasers”
- whole array is 2 types of signals → make threshold between them
- make sure to calibrate with door closed
- but we might want to know what the signals are when the door is open and closed (so we know when it’s serviced)
- can tell if door is opened or closed (serviced)
- complete circuit → the door is closed
- not complete → door open
- contact sensor
- magnets – complete the circuit
- light sensor – note every time it’s exposed to light (door is opened)
- not good because we don’t know dispenser would be filled all the way every time
- magnetic proximity sensor w/ coil inductors
- change in magnetic field
- draw wire to IO channel on Arduino
Power & communication concerns
- turn on and off by itself – idle and wake up after a certain amount of time
- trigger each time the dial is turned and reads tampon levels
- OR do a reading once when dispenser is refilled, count every time you turn dial
- wifi might be the right route
- less energy hungry
- problem: concrete bathrooms (cell signals are usually bad w/ concrete walls b/c there is metal inside them)
- cellular will drain power faster
- base station – wifi or cell, plug it in
- solar? phone could serve as communication & power harvesting
- stuck w/ cellular if can’t get access to power
- radio – no towers to receive it
- use dumb phone
- with big car battery?
- steal power off lights?