Hi, I’m in the same situation. The power off works great, but the lowest setting (1%) is almost as loud and powerful as the highest (100%) FET works fine, PWM signal is visible on the Gate pin. The output is also apparently switched well by the transistor. What pi-erwin thinks is saturation, I think is due to the output capacitor. I think even the lowest fill factor is too big for this fan. Quite simply, this fan works very efficiently, it can achieve high revolutions even with little current. It would be a solution if the PWM duty factor could be set lower. In the meantime, I replaced the 10uF capacitor with a 10nF capacitor, which is somewhat better. The speed change can already be detected between 1% and 100%. But this does not seem ideal from an electrical noise point of view.
How to access the minimum dutycycle? How can it be modified? Does the 8-bit microcontroller convert a 1-100% input signal to a 30(?)-100% output PWM signal? Or does the code running on the raspberry solve this?
I measured with the original capacitor between ground and the fan negative pin. (Thanks for the picture pi-erwin) 1%:
It can be seen that the negative pin barely moves away from the ground. So the full supply voltage is available to the fan even at the lowest set value. Therefore, there is no change between the different settings.
eight hours later:
As I see it, the 8-bit microcontroller converts 1-100% to 30-100% dutycycle. But there was also a little trick in “argononed.py” that caused my device to refuse to work below 47% fill factor. I commented out these two lines, so the output can already go down to 30%.
