Duet3 MB6HC Rev1.0 firmware 3.0beta12 can’t control PWM fan

Jimmykc

My fans configuration is showed below.

I jump wire to check the PWM signal by the oscilloscope.

I try to key the different fan command to control PWM.
M106 P0 S0
M106 P0 S1
M106 P0 S100
And I also slide the icon on DWC menu.

The PWM signal on the oscilloscope is no different.

dc42

Please upgrade first to RRF 3.0 and then to RRF 3.01-RC9, and see if the problem still exists.

Jimmykc

@dc42 Thanks for your help.
After I update to RRF 3.01-RC9, I can control PWM fan. But I have new question.
After I measure the out4 pin to check PWM signal, it is different from the PWM which I configure the io4.out as PWM.
The figure of PWM comparison is showed below

The Ch2’s PWM is configured from the io4.out.
The Ch3’s PWM is configured from the OUT4.
May I use fan PWM to control the servo ? or
Could you give me the suggestion how to use fan PWM to control the servo ?

dc42

The fan output are open-drain, so the signals on them won't make much sense unless you connect a fan or other load (e.g. a resistor) between the two pins.

It's possible to use a Fan- output to control a servo by adding a pullup resistor between that output and +5V, but why would you want to do that if you have a free IO_x_OUT pin?

Jimmykc

@dc42 I have servos more than IO_x_OUT pin so I want to use fan PWM to control them. OK, I will add a pullup resistor to try it. Thanks for your help.

dc42

@Jimmykc said in Duet3 MB6HC Rev1.0 firmware 3.0beta12 can’t control PWM fan:

@dc42 I have servos more than IO_x_OUT pin so I want to use fan PWM to control them. OK, I will add a pullup resistor to try it. Thanks for your help.

You will also need to invert the pin in the M950 command that creates a servo output using a fan pin.

Jimmykc

I add a pullup 3.3k resistor to 3.3V to try it.

It can work, but I have a new question.
What is the limitation of voltage for the fan pin if I want to pullup voltage more than 3.3V?

dc42

The limit is the VIN voltage.

Jimmykc

@dc42 I see, thanks.