- (EDIT: Flyback diode (such as a 1N4001) is not needed since Noctua already provides polarity protection, and a brushless fan typically already has it);
- (EDIT: No need for voltage divider) From Noctua documentation (https://noctua.at/media/wysiwyg/Noctua_ ... _paper.pdf), the RPM output is an open collector output (see page 3 of Noctua Doc.). This means that if the Vcc is 3V3, and R=1k5 Ohm, we should be fine (current is then limited to ca. 2.2mA);
- Resistence R2 (2K2) and transistor Q1 (2N2222A) are used to drive the PWM signal.
Wires connected to the Pi header:
Red: (+5V) Pin 2 (https://pinout.xyz/pinout/pin2_5v_power); (+3V3) Pin 1 (https://pinout.xyz/pinout/pin1_3v3_power)
Black: (GND) Pin 6 (https://pinout.xyz/pinout/ground)
Blue: (PWM Signal from Pi) Pin 32 (https://pinout.xyz/pinout/pin32_gpio12)
Green: (RPM Signal) Pin 36 (https://pinout.xyz/pinout/pin36_gpio16)
In other words:
- Is this circuit correct? Am I making any mistakes? I'm an engineer, but not an electrical one, so be kind...
- Noctua does not seem to recommend an open collector design (see below)... What alternatives do I have?
Again, from Noctua doc.:
Can you help?