PWM fan control over GPIO

General
1

Hi,
i want to obstruct the originally pwm fan

you can activate it by OS, but only on/off at 60°C over pwm gpio.

can I set the pwm by using gpio out:
grafik

I'm not sure, because you should only set it up to a maximum of 100 Hz says the node.

I thought fan control pwm works at about 25000 Hz ?
but I don´t know about the range of the original RPi fan.

2

So... what happens when you try a range between 0 and 100? Often an answer can be found by testing. Something we can't do from here, in your case.

3

What makes you think that it will not work with 100hz?

What makes you think that?

4

If you use a 4 wire fan:

Target frequency 25 kHz, acceptable operational range 21 kHz to 28 kHz

https://www.electroschematics.com/4-wire-pc-fan/
On raspberries the pwm freqency is limited (as it is software generated)

The minimum PWM output frequency is 10 Hz. The maximum PWM output frequency is 8 KHz using writePWMFrequency(mypi, 12, 8000).

Perhaps use a i2c pwm controller chip.

You probably don’t want to dedicate one core of your raspberry to generate a pwm signal too cool the cpu just because you generate the pwm to cool …. :sun_with_face:

If you use a standard dc fan you need a mosfet and filtering to run your fan smoothly. You can perhaps get rid of some filters on higher frequencies but you run into hearable hiss or other noises and emi problems as you push spiky pulses along a wire

1 Like
5

Quickly looking @ the spec they use the serial UART tx pin to drive the pwm. The serial controller probably able to generate the 25k.
So you probably take a look into that path.
But I’m not a raspberry expert. I would go the i2c path as it is always better to have real hardware pwm.

1 Like
6

I don´t have the fan here yet aaaand on the Pi4 Node-Red is not installed. :grimacing:

I think I give the os-fan controll a chance, but on off with pwm 0 / 1 should also be ok.

7

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