Automated Fan Speed Controller

By Bill Olson
Category: Home, Computers & Mobile, Workshop
Difficulty: Moderate

When our house was built, I put a server room next to my office. Unfortunately, it had only a small bathroom-style fan with a 4″ duct leading outside, and during the summer I had to leave the door open, which made my office hot and loud.

So I installed a larger fan, along with an 8″ duct that dumps the waste heat into our basement during winter and outside during the summer.

The new fan works well, but also draws a lot of power — almost 300 watts. To reduce energy usage, I installed a manual speed control, but this made the temperature vary too much.

Finally, I built a control system that automatically adjusts the fan speed to maintain a constant temperature in the room. I was already using a serial-port temperature sensor connected to a computer to monitor and plot the server room temperature, so I closed the control loop using a MAKE Controller, a stepper motor, and some Lego Technic gears to turn the manual speed control knob.

I considered getting a different temperature sensor that would connect to the MAKE Controller directly. This would allow the system to stand alone without the computer. But in the end I chose to extend my existing setup and simply use the controller as an interface to the motor.

Parts
/
Tools

Temperature sensor, with serial interface (1) I used a Hot Little Therm from Spiderplant (spiderplant.com) thatâ€™s unfortunately no longer being sold. You can also wire an LM35 temperature sensor chip directly to the MAKE Controller (and tweak my Perl code to read the temperature from the controller, rather than executing the â€œtermâ€Â program).
Fan control, electronic, variable-speed (1) Broan model #72W (broan.com)
MAKE Controller kit, v2.0 with application board (1) product #MKMT3 from Maker Shed (makershed.com), $120
Motor, stepper (1) such as All Electronics part #SMT-116, #SMT-113, or #SMT-119 (allelectronics.com)
Power supplies, wall-wart (2) to power the MAKE Controller and stepper motor separately
Lego sets, Technic beams, bushes, cross axles, and gear wheels (1) Lego sets #10072-1, #10073-1, #10074-1, and #10076-1 (peeron.com)
Electrical outlet box, deep (1) such as Wiremold/Legrand #B3
Host computer, with Ethernet adapter (1) The computer will need to be on all the time, but if youâ€™re cooling a server room (like me) there should be no shortage of computers.
Ethernet cable (1)
Plywood, scrap about 1' square (1)
Bracket, metal, for the end of a 2×4 (1) such as Simpson Strong-Tie #FB24
Screws and standoffs (4) for mounting the controller board to wood; I salvaged some from various ATX computer cases.
Weight, small tied to a string (1)

Steps

Step #1: Assemble the parts.

I mounted all the hardware onto a scrap of board. I screwed an outlet box onto one corner for the 2 power supplies, and drilled the wood to let the 115V AC wiring enter through the back.
I mounted the MAKE Controller in another corner using some hex screw standoffs, and I secured the stepper motor in a bracket sized to hold 2×4 studs.
Next came the connections. From the controller’s Application Board, Main Power connects to DC (I used a 10V DC, 0.3A wall wart), and an Ethernet cable connects to the PC. The motor has 5 wires; 4 connect to Digital Outs Bank 1 on the Application Board and 1 connects to ground. I figured out which went where by trial and error.

Conclusion

I had a lot of fun with this project. It taught me about microcontrollers and stepper motors, and even gave me an excuse to play with Lego. This was my first project using the MAKE Controller, which I was eager to try, and I’m already looking forward to my next “MAKE Controlled” project. Meanwhile, the fan control system has been very reliable during its 20-plus months of service.

This project first appeared in MAKE Volume 21, page 139.

One Response to Automated Fan Speed Controller

Dave Rongey on March 31st, 2013 at 1:21 am said:

This is really awesome – I love it! Bill has made good use of a variety of parts and brought them together to be used for a very creative application. I love building projects as well, and I have found that it is very helpful to understand what parts are available and then using your creativity to assemble the parts for a new application, and that’s what has been demonstrated here. Congratulations on your project!

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