Typically, the cooling fan is connected to the system through a three-wire interface, which includes a power cable, a ground cable, and a Tach cable (speed signal cable). In order to be able to read Tach signals through GPIO, you need to select a fan that supports this feature. Such fans are often referred to as "ach-enabled" (supporting Tach) or "RPM-sensing" (supporting speed detection) fans.

The Tach signal is a pulse signal whose frequency is proportional to the speed of the fan. Typically, a pulse signal is generated for each rotational speed cycle. Here are some steps to help you implement a cooling fan that reads Tach signals via GPIO:

1, Make sure that the fan you choose supports Tach function or speed detection function. You can find this information in the fan specifications and instructions.

2. Connect the Tach wire of the fan to the available GPIO pin. This usually requires the use of cables or connectors.

3, Use the appropriate hardware interface circuit to convert the fan's Tach signal into a digital signal that can be read. This is because GPIO typically operates at the digital signal level.

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