Ever wished those noisy fans weren't on all the time? or dont see the point in them being on when the computer isnt doing anything? Well, I can help you...

There we go, thats the finished article, well sort of finished anyway. Some trim around my dodgy dremel on blanking plate skills will finish it off. Anyway, thats not the point at the mo, its whats behind there that counts...

What you need (w/Maplin Codes):
1x Temperature Module - FE33
1x Probe for above - FE34
1x Stripboard - JP51
2x BD139 Transistor - QF07
2x Power Relay - UQ94
2x 1N4001 Diode - QL73
4x Push To Make Switches of your choice (I used FF96)
2x 330R Resistors - M330R
1x MALE Molex Connector - JW64
Various Wiring, Solder, Soldering Iron and the usual mod tools :)

The display

What does this circuit do?:
This circuit allows you to set two temperature thresholds using the switches on the front, a 'high' threshold and a 'low' threshold. When the temperature detected by the probe displayed on the LCD is below the lower threshold the fans are completely off. When the temperature is above the lower but below the higher threshold the fans are at 5v (or any other voltage you desire - explained later). When the temperature is above both the thresholds the fans are running at 12v. Thanks to the temperature module, this circuit does not switch the fans on and off rapidly, i.e. the fan must stay on for a minimum of 30s before being allowed to go off. The prevents them turning on and off all the time which gets annoying.

Lets get down to the modding... :)

Attaching the new probe:
The module comes as standard with a sensor soldered directly onto the PCB, but this isnt much use for taking the temperature of a remote source, i.e. the Graphics Card heatsink. Fortunatley for us we ordered the extra probe didnt we? ;)

Heres the module with the extra probe

After unscrewing the battery holder via the 6 screws (3 down each side) we can see the original sensor (circled).

The new sensor

All you have to do is unsolder the old sensor from the board and solder the leads from the new one onto the pads, it does not matter which way round it goes.

Fire up the iron!!

Theres the new sensor attached no probs :)

Now its time to knock up the PCB with all the goodies on and attach it to the temperature module...

Building the circuit:
The following is the schematic for this circuit, I know it isnt particularly clear so if you have any questions feel free to mail me.

Ill just give you a quick explanation of how it works...

Lets assume that the temperature is inbetween the two temperature thresholds. This means that both of the relays are in the NC position (normally closed). This sets the fan output at 5v.

If the temperature falls below the lower threshold the temperature module sends +1.5v from pin 7, this allows the transistor to conduct and so the relay switches to prevent any current from going to the output, hence the fan goes off.

If the temperature rises above the higher threshold the module sends +1.5v from pin 6, this, again, allows the transistor to conduct and the first relay switches. It switches over so that it is giving 12v to the second relay instead of the usual 5.

Now all you have to do is build that schmatic onto your stripboard (you will have enough if you ordered that number that I gave you ;).

There's my board finished

Once you have built that circuit its time to connect it to the actual temperature module.

The Pinouts:

There, that should be enough information for you to be able to complete the project. All you have to do is mount it now, but ill leave that up to you because we all have different tastes ;).

Im currently working on a backlight for it, and will probably be inverting the display (like all my others ;) so you can look out for those soon I think.

Once again, any problems just mail me.