I wish to use a simple way to turn on-off a 4 wire cpu fan using a digital output of the Arduino board. Since even with PWM=0 the fan works at 30% of the full speed, i have to find a way to cut off the power of the fan.
I came across some tutorials describing the optocoupler 4N25, so I decided to give it a try. For that purpose I didn't use the Arduino itself, but two separate powers of 5V and 12V.
The schematic shows exactly what I did first, and it worked fine. The LED was turning on and off accordingly to the switching of the left hand cirquit.
After that I tried to connect the two wires of the fan (ground and power) in the (4) and (5) pins of the optocoupler, but the fan failed to respond to the commands of the switch, actually it didn't start at all. I guess that I miss something there.
I also tried to ground pin 6 (ground) with no success.
This is the type of the fan I am using: http://www.formfactors.org/developer/specs/REV1_2_Public.pdf
Any suggestions would be appreciated
Thank you in advance