using gpo's to vary fan speed

jleach · Post by **jleach** » Mon Mar 25, 2002 6:46 pm

I'd like to use two of the GPO's on my LK204-25PC to vary the power to two or three of my case fans like this:

GPO1 GPO2 Fan Voltage
OFF OFF 12v
ON OFF 7v
OFF ON 5v
ON ON 0v (off)

Unfortunatley, I don't know how to design a circuit to do this. Heh. Anyone care to help? I think this would be a great way to vary the voltages to your fans by software. 12v is the default with both GPOs OFF because they're off by default and the fans get 12v by default... just seems right.

Let me know if you have any ideas.

Cheesekeeper · Post by **Cheesekeeper** » Mon Mar 25, 2002 10:18 pm

I had the same idea a little while ago - it can be done, but I'm waiting for my LK204-25 to arrive before I can test it out. The circuit only needs 2 relays, and pretty much nothing in the way of baord design (I'm just using Veroboard).

The first relay switches between 5V and 12V, and the second switches between 5V and 0V. Once I have this working, I'll be writing an LCDC plugin to control it. Note that LCDC can sort of do this in software, by pulsing power to a 12V GPO, giving you 3 speeds (full, ~50%, off).

I'm a little worried about how long the Display can keep pulsing the GPO before the smoke escapes, so I'm going to stick to the 4-speed relay idea instead........

Post by **Henry** » Tue Mar 26, 2002 10:07 am

Sounds good

Post by **Mat-Moo** » Tue Mar 26, 2002 10:10 am

Henry assures me that the GPO's will handle that with no problems