Olimex ESP32-EVB Dual Fan Add-On

This is an untested add-on board for Olimex ESP32-EVB for controlling two standard 12V four-pin PWM fans.

In addition to controlling the fan PWM and observing the fan RPMs (via tachometer inputs; two pulses per rotation), one or both fans can be powered down completely.

On the PCB, the two Vishay SI2393DS-T1-GE3 P-channel MOSFETs in SOT23-3 are marked as G6, the six Nexperia NX138AKR N-channel MOSFETs also in SOT23-3 are marked as AP, the four 220Ω resistors in 0603 as 221, and the six 10kΩ resistors in 0603 as 103.  These should match the markings on the corresponding components themselves.

There are two 3mm holes for mounting, their center-to-center distance being 45mm.