3-Wire Cooling Fan Monitor Circuit - ElectroSchematics This little adapter circuit can be used with any 3-Wire instrument cooling/exhaust/blower fan. In a 3-wire fan, first two wires are the power supply wires of the fan. The third wire, comes directly from the output of the built-in ‘Hall Sensor’ chip generates output pulses during the fan rotation. Motherboard (CPU) 4 Pin Fan · AllPinouts Fans and on-board fan headers are backwards compatible. Proper fan connector placement is shown in the figures below: Fan has a 3-pin power connector; desktop board has a 4-pin fan header: Note: when using a 3-pin power connector with a 4-pin fan header, the fan will always be on; there is no fan control. Fritzing Project – Connect, control and read an 4 wire fan. This project shows how to connect, controland read an 4 wire computerfan, INTRODUCTION. This is the first one of several little projects that i intend to upload, they explain the working of usual or undocumented parts that i experimented with. To power the fan you need an external powersource, in this case i used a 12 volt 1,5Amp DC Adapter.