RRC[

Rat Rig Community [Unofficial]•3y ago

MFBS

Has anyone hooked up a CPAP fan WS7040 to an SKR Pro 1.2 board?

Warning I barely understand enough about the electronics to frame the right questions and I haven't been able to find the relevant documentation in a form I understand yet.

I don't believe I can drive it from the 24V fan port as the SKR Pro 1.2 can't supply over 1 amp. It is easier enough to supply the 24V to it directly from the PSU.

I am trying to work out the best way to PWM it. I know I can do this direct from a GPIO port on the Raspberry Pi but that has two issues.

1. The GPIO pins are I think only 3.3 volts and ideally I want 5V PWM...be a good party trick to drive it at full speed for giggles.
2. If I PWM it from the Raspberry Pi fan will turn on full blast I think, until the Pi has booted.

This is the WS7040 fan and daughter board I am using.
https://www.aliexpress.com/item/1005004729010078.html


I am not sure:

1. Which would be the best pin to try and PWM it from the SKR Pro 1.2 board? Would PC9 be a good option? Is PC9 5V?
2. Because as soon as I hook the fan up to 24V it goes full blast I suspect the WS7040 daughter board has an internal pull-up like the 4028 fans have? If so it might need to pull the PWM down to ground until the Pi has booted.

I might be able to use a pull-down resistor on a digital pin like PC9 to over ride it until the Pi has booted like I did with @eleco's excellent set-up for the 4028 fan? But I am also not sure if this pin is 5V capable or only 3.3V capable?

3. If the WS7040 has a tach output that I could hook up to PF9?