Inside an automatic foam soap dispenser with clever pump.

I was expecting this unit to be based on a single motor driving a separate fluid pump and aeration system. But they've got a very clever pump system that combines the two into one.

The infrared sensor seems to put out four pulses a second. I didn't reverse engineer the op-amp section because I have a feeling that it may just be a pre-filter and amplifier, with the microcontroller processing the resultant voltage level via an analogue input.

On eBay this type of unit has the description:-
350ml Automatic Foam Soap Dispenser Infrared Motion Sensor Touchless Hand Washer

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