Computer fan speed tacho out circuit - Add a fan speed monitor lead to any 12V two wire fan. HOME

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

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Do not experiment with or build any of the above circuits.