Part and cost reduction

[bob-u]

Great project. This is basically a fan proxy - very similar to what I've been thinking of making. I'm glad I found this project and thank you for sharing. Given the part shortages, what do you think about also using 74HC4051D for reading PWM input from the motherboard and substituting level converters with PC817 opto-couplers?

I also want to present the temperature sensor output to lm_sensors via USB.

[tjko]

I have had no issues getting any of the ICs, but I guess things are not 'stable' yet.... I went with these since at the time I was designing the initial schematic these were in plenty of supply and they conveniently had ESD protection built-in, etc...

I don't see problem adding support for boards to use multiplexer for (motherboard) PWM input. There is already similarly support for two different ways for boards to implement reading tachometer signals (directly or via multiplexer)...

Were you thinking of putting optocouplers before the 74HC4051 (one for each input)?

For lm_sensors, where you thinking making device appear as 'hwmon' device in USB bus? Or adding lm_sensor 'driver' that would simply issue SCPI commands to get the data?

[bob-u]

For interface I was thinking of:
USBTMC via tinyusb for pipico: tinyusb
liquidctl for client: liquidctl
liquidtux for hwmon: liquidtux

EDIT: I did not realize that fanpico has a fully working SCPI interface already. There's hwmon scpi module but in 2017 it was restricted to ARM builds only. Still, it would probably be easier to change the complie flag then add new code into kernel (what some had been trying for years).