How to enable the 2 pin header on RockPi 4c

#1

Hi everyone

New post from a newbie!
I have searched for an answer but I am not finding any information so please forgive me if this question is already answered.

How do I enable the 2 pin header on the Rock Pi4c for fan connection?

The specification says it can be used with PWM, but I can only see how to enable PWM on the 40 pin connector. I will be using the 40 pin header so I want to transfer the fan to the 2 pin header.

Any help welcome!

#2

Still need some help here !
I’m using image rock-4c-plus_debian_bullseye_kde_b55
But any pointers for other distros welcome

Thanks

#3

I have seen posts on pwm use on other boards. There are two disabled rk3399-pwm*dto files in /boot. You might start there. And I think in rock 5b boards either in this forum or discord , there are instructions on implementing a script and “pwm curve” that may apply to this as well. I don’t use it, i just connect to 5v / grnd pins on gpio and let it run full on. The NAS, 3d printer, work laptop dans, tv, music or other usually drown out that annoying fan noise. LOL

#4

Thanks for the reply - will check that out

#5

I checked out the links and started looking at the directories in Debian and I am probably more confused than before!

To ask a simpler question…can I enable 5v on the 2pin header?

In other words forget PWM for the moment.

#6

Finally I have a solution after some research, hints from other models and some experimentation.

I have two small fans connected to the 2 pin header and I can control by writing to
/sys/class/thermal/cooling_device2/cur_state
0 off, 1 single fan runs, 2 both fans run quiet, 3 both fans full speed

Writing with sudo nano worked but the change was not persistent and reset after boot.
Tried using echo in a bash script to run at startup but hit permissions errors.

Solution was adding a udev rule:
/etc/udev/rules.d/02-radxa-fan.rules
ACTION==“add|change”, KERNEL==“cooling_device2”, SUBSYSTEM==“thermal”, ATTR{cur_state}=“3”

The fans now start on boot and stop on exit

Some useful commands that may be obvious to others but were not to me…
Test rule: sudo udevadm test /sys/class/thermal/cooling_device2
Start rules: sudo udevadm trigger or sudo udevadm control --reload
Check attributes: udevadm info -a /sys/class/thermal/cooling_device2

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