Here’s what we did for the Purell sanitizers (model 2720-01).
We desoldered the AA battery packs from the motes and set them aside. Instead we made a circuit with a battery that parasites from the 3 C cell batteries in the Purell.
There are two wire pairs connected to the Purell. The red and black wires go through a hole near the dispenser outlet, avoiding the moving portion, and into the black box. Avoid the cam, which moves, and solder to the battery terminals. The other pair of wires (yellow and blue) go to the motor through a hole which is drilled out of the motor case top. The other end of these wires goes to the 3-pin connector on our circuit board (vl parasite 3.1 on the server). The center pin of the connector goes to the positive side of the motor.
The circuit board was made in the electronics shop. There were two versions, but we think all the current Purells have the version marked 3.1 on the circuit board.
These components go on the circuit board:
1. Female MTA socket with wires and header .1 spacing, 2 pin
2. Female MTA socket with wires and header .1 spacing, 3 pin
3. Optocoupler Isolator Phototransistor 50 MA CTGR-20% DIP-6.
4. 330 ohm resistor
5. 2 resistors (resistance marked in the eagle circuit board file)
5. VL2020 horizontal mounted battery (BATTERY LITH COIN 3V 20MM HORIZ – about $5 from digikey).
6. 4 wires to connect with the mote. (Note: It would be nice to have some connector here so the mote could be detached from the Purell.)
7. IC Linear Regulator Voltage 3.3V, 300mA, (LDO TO-92?)
Two 4-40, 3/4″ screws connect the board to the Purell below the push button.
There are 4 wires from the board to the mote. Assuming that the board is mounted in the purell with the connectors on the right, towards the center of the device, up towards the soap dispenser, we’re labelling the wires from the top down on the left side of the board.
Top is ground (near the voltage regulator)
Next down is power.
3rd down is analog input (a voltage divider so the mote can read the voltage).
Bottom is user button interrupt.
The mote tucks into the case on the left.