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 GideonTech Projects

-- Variable Speed Fan Controller
-- 01.30.2004
-- By : Skylined
-- Page: 1 2 3

Today we will be constructing a variable speed fan controller that incorporates these three options:
- Variable (6.5V to 10.5V)
- 12V
- Off

You may ask why does the voltage drop from 12V to 10.5V. That is because the voltage regulator we are using will drop the voltage by 1.25V, causing our maximum voltage output to be around 10.75V. In order to push the fan up to 12V we have used a switch that connects the fan directly to the PSU's 12V line. Unfortunately, we cannot set a voltage from 10.5V to 12V.

We've sacrificed that 1.5V for some good reasons:

  • Ability to have RPM sensing
  • Starting voltage is most fan's starting voltage
  • Support of 1.5A in variable mode
  • Full use of potentiometer range
  • No fan's rattling
  • Increased potentiometer sensibility
  • Easy to find and cheap potentiometer


  • Proto PCB - $3
  • LM317 - $2
  • Potentiometer 5KOhm 1/4W - $3
  • 1uF Tantalum Capacitor - $1.50
  • 100nF Ceramic Capacitor - $1.20
  • 470Ohm 1/4W Resistor - $1 for a pack of 5
  • 1K2Ohm 1/4W Resistor - $1 for a pack of 5
  • 4K7Ohm 1/4 Resistor - $1 for a pack of 5
  • Bicolor LED - $1.50
  • 3.5mm Stereo or Mono Jack - $2
  • DPDT Switch - $1
  • Heatsink for LM317 - $1.50
  • Knob - $1
  • Soldering Iron Kit
  • Heatshrink
  • Wire

Prices at Radio Shack 12/05/03*

*Thanks to renderblender for getting the prices.

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