I'm having a bit of trouble here. I am a sophomore Computer Engineering student at Psu. I recently bought a new computer case, and the front has an 80cm fan with LED's and what-not. The problem is that it is very loud. To make matters worse, it runs on a four-pin molex, and the speed isn't variable. Additionally, I share the room with a roomate, and the lights are kinda bright, esp. when its dark. The case is acrylic, and the side panels are screw-on, so I can't even unplug it.
Now my Idea is to use the 'reset' button, which is useless with a 'power' button above it, to change the speed, as well as turn it off.
My plan is to us a binary-output counter (SN74LS163), and tie the one's and two's places into a 2 to four DMUX (Say an SN74LS139A). I'll then use the momentary switch(reset button) as the clock for the counter. This will let me cycle between four different circuits: Unmodified, 80%, 40%, and off.
Now implementing the logic is no problem. The issue I have is using the 5v logic outputs to actually control the 12v fan. I looked into Tri-State buffers, but even if I was able to find one that took 5 and12 volt inputs, none have the necessary 150 mA capacity. Now I talked to an EE buddy of mine and he suggested that I could use a few transistors to switch it. Alas, transistors aren't one of my strong points, and I dont know how to use them, or even what type to get. I pretty much need to use a 5v, 20 mA max low/high signal to start/stop a 12v current that may go up to 250mA, without frying any ICs, and can last for at least two years of continuous use.
I tried searching the internet for a few hours, but couldn't find the info I needed. I eventually found this group, and I'm hoping somebody here can help.