Fixing a faulty schmoo pump

My hand soap dispenser started to get slower and slower, even with fresh batteries. So I decided it was time to open it and see what was wrong.

Even with hand pumped foam dispensers, the fine metal or nylon mesh used to add the final layer of creaminess to the foam is prone to blocking over time with waterborne "stuff" (possibly organic).

It's nice that this unit is actually serviceable, with both the pump and the schmoo-plumper suited to complete disassembly for cleaning.

Quiescent current of this unit is around 2mA due to its need to continuously pulse the infrared LED. The microcontroller will turn the LED on then check the voltage from the photodiode and then turn the LED off again. It is usually only lit for as long as needed to get the reading.
When it detects a sudden increase of infrared light reflected, it runs the schmoo-pump briefly to dispense the creamy schmoo.

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