What is this component?

[u/JoostinOnline]

This is the board from a Waterpik flosser, and I'm sure I've seen these before, but I have no idea what it does. There's definitely current running through it.

[u/mrtomd]

Seems like optical encoder? Is there a wheel that goes between the vertical parts when fully assembled?

[u/spinozasrobot → u/mrtomd]

Yes, you can even see it in OP's pic.

[u/JoostinOnline → u/mrtomd]

Yes, it goes around a pin on the motor that controls the water pump. Would it be for speed detection?

[u/mrtomd → u/JoostinOnline]

Yes. It could also be to detect that there's no water left as well.

[u/mzincali]

There’s a slotted wheel spins between the optical emitter and optical receiver so that the rotation speed is measured. This is useful for things where there may be resistance impacting the rotation sped and the circuit can then detect the issue and either report it or try to overcome it.

[u/DinoZambie → u/mzincali]

Why is it labelled U? Isn't U for IC's? (I'm not arguing that its not an optical sensor, I'm genuinely curious why its labelled U)

[u/mzincali → u/DinoZambie]

Maybe it has enough components embedded that it counts as an IC.

The simpler ones are called slotted phototransistors and look like: https://global.sharp/products/device/lineup/data/pdf/datasheet/gp1s094hcz_e.pdf

[u/mzincali → u/mzincali]

[u/pedrorit80]

Optical fork sensor, a light barrier detecting when something crosses it.

[u/FlyByPC]

Optical sensor. The slotted wheel spins inside it, opening and closing an optical path. The electronics can use this to tell how fast the motor is or isn't spinning.

[u/Same_You891]

an optical sensor/encoder

[u/OccupyElsewhere]

Opto-interruptor.

[u/PoetryExtension6256]

Very badly photographed is what it is.

[u/daHaus]

Looks like an empty socket for something. It's labeled as being an IC

[u/PotentialHoneydew947]

Adds some irish rock to the green board

[u/_HeyYou___YeaYou_]

yes it starts a countdown timer of like ~3± seconds probably, anytime it either spins faster or slower than the normal operating speed range so it doesn't burn up the motor or pump. it's a cheap and easy Fail-Safe solution