Low Cost Air Flow Sensor

 simple air flow sensor using scrap parts.

simple air flow sensor using scrap parts.

1, mouse center wheel
2, heat shrink tube 
3, used ball pen refill
4, lm358 comparator circuit
5, acrylic sheet
6, IR slot sensor

MOC7811 is a slotted Opto isolator module,
with an IR transmitter & a photodiode mounted on it.
Performs Non-Contact Object Sensing. This is normally used as positional sensor switch (limit switch) or as Position Encoder sensors used to find position of the wheel.
It consists of IR LED and Photodiode mounted facing each other enclosed in plastic body.