Right, back again with an update on my idea for a kick-ass fanctroller. So far, I've been coding away and right now, I'm up to the point where the actual fan control is implemented (I've already written the LCD-commands, several input functions, a setup and a menu.) But I'm having some problems.
Now that the software is nearing it's end, I'm starting to think about the hardware again. I want to create a custom PCB for this thing. One of the things that bug me the most is the fan power delivery circuit. After a lot of testing (and I mean a lot), I came to the conclusion that the 3-pin fans I intend to use need a true analog voltage. If they're powered by PWM, the fan-speed readout is completely wrong.
That's where I'm at right now and I'd appreciate your input. How can I convert the PWM output (0-5V) of my arduino to a linear analog voltage between 0 and 12 volts with a power supply of 12 volts? I tried using the schematic below, but that gives me a maximum voltage of about 10.5 volts (because of the voltage drop over the darlington). Does anyone have a better idea?
R1 is the load (one or more fans/pumps)
R2 and R3 have been fiddled with endlessly
Q1 is a TIP112 Darlington pair
U1.1 is one of the two opamps in the TS272CN package
The most left wire goes to the PWM output of the arduino