This fan speed controller was designed for my Automated Mushroom Cultivation project.

Description

A board to control the speed and measure the RPM of Terrabloom EC duct fans with a Raspberry Pi. It convert a 3.3-volt PWM signal from a Raspberry Pi to a 10-volt PWM that’s sent to the fan to control the speed. The open collector tachometer signal from the fan is pulled to 3.3 volts and can be read by an input pin to measure RPM at 2 pulses per revolution. This was designed for fan speed control and RPM measurement using Mycodo. Circuit designed by lemonsquash11.

PCB Components

The 4 pins to the Pi (3.3v, GND, TACH, and PWM) have a standard spacing of 0.1 inches (2.54 mm) to use any number of through-hole terminal blocks or connectors.

The surface mount pads on the opposite end of the board are spaced at 3.56mm on center, with the pin configuration designed to work with this panel mount female TRRS audio connector. This will allow connecting directly to the 4-pole male-to-male audio cable supplied with Terrabloom EC fans in order to connect directly to the fan and control speed and measure RPM.

The two 3-pin components are NPN transistors (tested with 2N3904). Ensure the orientation is correct for these to work.

The five two-pin components are resistors, with values 3.3k (x1), 10k (x2), and 1k (2x). The value for each resistor is on the silkscreen to determine which goes where.

The Pin configuration is 1-GND, 2-10V, 3-PWM, 4-TACH. Each pin number is stamped on the metal pin of the connector.

Note

Be sure to double check the connections of your audio connector before soldering to the board (as you may have an audio connector with different pinouts) and that the proper pins Raspberry Pi are connected to the board. Also, ensure you plug in the audio cable to the board and to the fan before powering the fan. This circuit should also work with other single board computers and microcontrollers.

Alternate versions of this board exist with a 2.54 mm pitch and 5 mm pitch to give you more connecting options.