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【CW32】PWM fan speed controller

Overview

aim of design

I have several server fans that rotate at 10,000 rpm, but they are too noisy when used. I just added a voltage divider resistor to the speed reduction cable, which consumes power. To control the fan speed, develop a controller.

Schematic design instructions

The power supply part has a 12V input, which directly powers two fans. The voltage is reduced to 5V and connected to the fan control port. The 5V voltage is reduced to 3.3V to power the controller. 12v-5v uses the MT2492 solution, and 5v-3.3v uses the 1117 solution.

In the fan control part, each fan occupies 2 GPIOs, one outputs a 24kHz PWM signal for speed adjustment, and the other collects the fan feedback speed. Since the fan feedback speed is a square wave with a duty cycle of 50%, and only the frequency is related to the speed, only one GPIO is needed to collect the rising edge or falling edge.

The control signal and acquisition signal use MOS for level conversion.

PCB design instructions

Fixing holes are drilled in the PCB and are compatible with 9CM fans, which can be directly screwed to the fan position.

Software description

The software part rewrites the official GTIM timer routine code, inputs the duty cycle percentage, calculates the count value, and performs interrupt output.

Code block:

PosWidth = ( int )( 125 * Percentage / 100 );

Physical display instructions

In the demonstration, the speed control is set to 60%, and the output duty cycle is 60% PWM signal.

Precautions

Tip: Here are some precautions that need to be paid attention to in the production of the work (if not, you can leave it out)

Design Files

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Update:2025-05-18 08:57:24

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