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What I am trying to design is a 12 V DC controller for a PWM fan that uses a 100 Hz input signal and reversed duty cycle between 8 and 87 % to drive it. What I mean by reversed is that the fan is on full speed when at 8 % duty cycle and 87 % duty cycle yields minimum RPM (88 % will turn it off). I need to use a 0-5 VDC analog temperature sensor as an input signal and scale the duty cycle against it, 0 V being off, and 5 V full on, with a linear increase of speed in between. So a 0 V DC signal input to the controller would provide a 100 Hz 88 % (off) duty cycle signal from the controller and 5 V would provide an 8 % duty cycle (full speed) signal to the fan.

The controller doesn't handle the high current side of the fan at all, the fan has it's own wiring directly to the battery for that, so no relay or transistor would be required in the controller. If the controller is off, so is the fan.

Future plans for the controller would include a separate input that when triggered by a 12 V DC analog signal will cause the fan to go to max RPM (8 % duty cycle), and adjustable on/off points based on the 0-5 V DC input (narrowing the input voltage window [1-4 V DV, or 2-5 V DC, etc] to scale the PWM duty cycle against).

I'm not an electrical engineer by any means, but I do understand most concepts and parts involved in circuitry. I have been trying to build this device using off the shelf assembled PCB's but I couldn't find a pre-fabricated solution to scale the duty cycle in reverse based on the 0-5 V input.

I know it's a lot, but any help is greatly appreciated!

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    \$\begingroup\$ Welcome! A 5 V microcontroller would do what you want with about 20 lines of code. \$\endgroup\$
    – winny
    Commented Oct 27, 2022 at 12:15
  • \$\begingroup\$ Can you find a pre-fabricated solution to scale the duty cycle (not in reverse) based on the 0-5 V input <-- could you find this? \$\endgroup\$
    – Andy aka
    Commented Oct 27, 2022 at 12:21
  • \$\begingroup\$ I agree with Winny. Unless you want to build and learn about a lot of analog electronics (that's cool too!), a simple microcontroller is the way to go here. \$\endgroup\$ Commented Oct 27, 2022 at 14:09
  • \$\begingroup\$ I do have a controller that will scale the duty cycle for the 0-5v input, but it scales it in a positive direction instead of reverse. A Google search yields an insane amount of options and platforms for a microcontroller, I dont even know where to start. Ugh. Most solutions I've researched seem to indicate this as well, but I have no idea how to program something like that,, whereas I am more than capable of assembling circuitry. Thanks for the suggestions. \$\endgroup\$
    – TronCarter
    Commented Oct 27, 2022 at 22:05
  • \$\begingroup\$ Look into the Arduino platform. Great place to start for beginners with microcontrollers. \$\endgroup\$ Commented Oct 30, 2022 at 20:09

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