I have a case type 12 V 3-pin fan and I would like to connect its tach signal wire to an ESP32 input pin. Power supplies to ESP32 and the fan are separate, but the ground wire is common.
Based on some posts in google, internally the tach wire gets connected to ground wire twice during each fan rotation cycle. If it is that simple, should I just connect this wire to an ESP32 input pin and have a pull up resistor connected to 3.3 V? If so, what is the minimal reliable current or range the resistor should be calculated for - is it 12 mA or less? Or can the ESP32 pin be configured to use an internal pull-up resistor so the external resistor is not required?