Computer fan speed tacho circuit

Add a fan speed monitor lead to any 12V two wire fan.

You will find this identical circuit inside most 3 wire computer fans with speed monitoring output to the motherboard. Peel off the sticker from the fan hub in order to access a motor winding pin for connecting up the tacho circuit.

Circuit Diagram aka Schematic reverse engineered from circuit board

Safety, accuracy and completeness of information provided herein is not guaranteed,
so be inspired by it but do not use it as a basis for experimentation or other actions.

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