DIY Dual Fan Controller Full Project

The controller project is an aid for regulating two fans which works by cooling with the first fan when the sensor detects a variable temperature and turns ON the second fan when the temperature exceeds 5 degrees over the changing temperature.

Each fan will turn OFF when the temperature 5° below its turn-ON temperature which prevents the fan from cycling ON/OFF rapidly. One of the analog-to-digital pins of the 8-pin Atmel ATtiny45 microcontroller is used to measure the voltage divided between a 4.7K Ohm fixed resistor in series with a BC component. Based on the temperature, the thermistor changes its resistance in a predictable way.

The same method of converting its resistance into a voltage is being followed by a user-adjustable potentiometer. The thermistor voltage is represented as an 8-bit number from 0 to 255 after being read into the microcontroller. To perform the actual voltage divider-to-Fahrenheit calculation, the microcontroller can be programmed although the calculation is very complex, instead of using a table.

The types of fans used can be standard brushless PC box fans with 12V wire and ground wire. The main fan controller box contains mounting holes, and master power switch.
Read more