Momentary Switch to Toggle Fan.

ghosttwo · 2007-02-12T02:55:59+00:00

I'm having a bit of trouble here. I am a sophomore ComputerEngineering 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 isthat it is very loud. To make matters worse, it runs on a four-pinmolex, and the speed isn't variable. Additionally, I share the roomwith 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'teven 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 theone'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 thecounter. 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 usingthe 5v logic outputs to actually control the 12v fan. I looked intoTri-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 talkedto an EE buddy of mine and he suggested that I could use a fewtransistors to switch it. Alas, transistors aren't one of my strongpoints, and I dont know how to use them, or even what type to get. Ipretty much need to use a 5v, 20 mA max low/high signal to start/stopa 12v current that may go up to 250mA, without frying any ICs, and canlast for at least two years of continuous use.I tried searching the internet for a few hours, but couldn't find theinfo I needed. I eventually found this group, and I'm hoping somebodyhere can help.Cheers.

Feb 12, 2007 20 Replies

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John Fields 19 years ago

Can\'t imagine why not, it comes through fine on another system here.

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Momentary Switch to Toggle Fan.

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