This project is a controller for three standard PC fans, controlled by a computer program(Windows 7/10 tested). Video with a demonstration:

https://youtu.be/8hW6mBzUgN4?list=PLEL7qGoBXwEaDuzdx020j9YMi9B89LieX

Schematics provide two versions of the board, one - using Arduino Nano and ULN2003(Darlington transistors package), first photo from upper, and second - using ATmega8 CPU and three MOSFET transistors in the TO-220 case(for example IRF540/IRF640/IRF740).

I developed only the first one in PCB format, the second remained in prototype format(last photo). I like the first option because ULN2003 is popular chip that integrates everything from current-limiting resistors to protection diodes in a circuit that only requires a few components:

According to the documentation for ULN2003, the chip can output 500mA per channel, if you look at my schematic, you will see that I have paralleled two outputs for the FAN2 and FAN3 - they can output up to 1000mA per fan, and fan1 has three outputs connected in parallel, correspondingly, the output current can be up to 1500 mA, that is, a more powerful fan can be connected here. However, MOSFET solutions can produce several times more output currents.

You can use both solutions, Arduino Nano or ATmega8, but in the case of ATmega8, you need pre-flash the firmware(with Arduino IDE) and next step - connect a USB-UART adapter to J2 (baud rate 9600), ATmega8 solutuon - need supply +5V for the J2, Arduino Nano have all this in board.

More informations about project on Github:
https://github.com/techn0man1ac/SoftReobasArduino/