4 ms·
I guess the microcontroller controls a fan using PWM with a duty cycle depending on the mode. Even if you could do it with a 555, it's easier to just do it with
by retSava 9y ago
I guess the microcontroller controls a fan using PWM with a duty cycle depending on the mode. Even if you could do it with a 555, it's easier to just do it with a microcontroller. It also makes it easier to make changes up until production without changing hardware.
- lmilcin 9y agoNo, it controlled it through a Darlington array controlling an array of mechanical relays. The fan has 3 220V AC inputs and selecting the combination of inputs changes the fan speed. I haven't looked inside the fan because it worked correctly. I also didn't want to test it to see how it works so I figured it out by analyzing the PCB. Actually that was quite good idea because the relays seem to be connected in such a way as to only allow valid combination to be sent to the fan even in case of invalid input from the microcontroller. I suspect bad things would happen if I sent incorrect inputs to the fan -- looking at how crappy the board was but at the same time that the person put effort into placing the relays to explicitly disallow invalid combinations of power lines to the fan.