Following recently published article about building a PWM Fan Controller here is another simple controller design. This time it’s a 2 Channel PC Fan Controller for standard 12V Fans. It uses software implementation of PWM but instead of directly driving PWM Fan the output is converted to 3 different voltage setting: High +12V, Medium +10.5V and Low about 9V.Each channel can be individually controlled by two push buttons SW0, SW1.The software is a modified assembly code from Microchip Application notes AN1074 for 12F615 MCU. I’ve changed some configuration settings ,PORTs assignment and added switches scanning routines to adjust it for PIC16F876A
Each channel requires a simple calibration. While in High mode (Max RPM) adjust 10k variable resistor connected to LM317