Momentary Switch to Toggle Fan.

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 and

12 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.

Cheers.

Reply to
ghosttwo
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Several hundred people here can show you, very simply, exactly what you need to do with the output of yout TTL IC to feed your fan so it goes on and off as you dictate.

But ask yourself one question..........

Why do you think the fan is there in the first place? Just to annoy your roommate?

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Reply to
Gibbo

Get a quieter fan, maybe. allelectronics.com has an 80 mm fan, part number cf-257 for $3.50. Says it's 21.0 dBA...

Reply to
kell

There's rumored to be a CMOS COOKBOOK with the circuits you need in it.

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Many thanks,

Don Lancaster                          voice phone: (928)428-4073
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Reply to
Don Lancaster

You obviously have never met his roommate.

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Many thanks,

Don Lancaster                          voice phone: (928)428-4073
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Reply to
Don Lancaster

Buy a quiet fan.

Reply to
Homer J Simpson

Several hundred perhaps, but can you?

I live with Mike Tyson. He'll bite my face off.

This is one of those little pet-projects that I want to do regardless of the neccessity. There are two other molex fans in the case, withought lights, and I've aready ordered three-pin replacents, as well as a green cold cathode strip light. But the front fan is special. I want to be able to build a little board with a female molex and some pins soldered on, and I can just plug everything in an have it work. The only hurdle left is what transistors to use, and how to connect them. Additionally, is there a better way to implement the switching besides a counter+dmux? This design is simpler, and has less wiring than a J-K solution, so I'm thinking its the best choice, esp. as I have all of the neccessary parts.

Reply to
ghosttwo

Found an excellent resource:

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This page seems to clear up a lot of the uncertainty about the outputs. I'm going to draft up a schematic and run it past another EE buddy.

Keep in mind that other people with the same situation may come through here on a google search, and it would be good to have clear, concise, solutions. I may post up a schematic, and let ya'll know how it goes.

Reply to
ghosttwo

Don, your humor has been showing lately. I liked your answer to the guy that wanted to melt ice off the driveway. "The obvious solution is to move the driveway to where there is no ice."

From sunny Florida, Mike P.S. I don't miss winter in Michigan

Reply to
amdx

Then you need to chose your boyfriends with more care. he would probably bite the computer, too.

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Reply to
Michael A. Terrell

He just copied some guys TTL COOKBOOK. ;-)

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Reply to
Michael A. Terrell

snipped-for-privacy@gmail.com wrote in news:1171267653.479253.174030 @j27g2000cwj.googlegroups.com:

You could also look here

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Reply to
me

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Yes.

I\'ve emailed you a schematic since you can\'t access
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Reply to
John Fields

I got your email, however it was all garbled. I saw the words 'Fanspeed.pdf' So I assume you meant to send it as an attatchment, not as ascii text. I'm interested in seeing what your version looks like, and how it compares to my own.

I don't have access to a scanner right now, but the general layout is a four-bit counter with the 1's and 2's places fed into a 2-to-4 Dmux. The first three Dmux outputs each go to a PNP transistor, which mediate the current to the fan, while the fourth goes to ground, disabling (or rather, not enabling) the fan. As each output is selected, the output goes from high to low, allowing the 12v current to pass through the Transistor(s).

Total # of parts: Two ICs, Seven resistors, three PNP transistors, a capacitor (used to stabilize clock), and various wires and connectors. Done properly, it'll take up less space than a saltine cracker, and depending on the quality of the ICs, last for years. Total cost: less than 5 bucks, esp. since I can get most of the parts for free.

Reply to
ghosttwo

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Reply to
John Fields

Awesome. Data sheets=good! I don't know if I'll be able to get one of those chips or not, but do you have a schematic for this design?

Reply to
ghosttwo

There's just one thing I don't get. After you turn the fan down, what's going to keep your computer from overheating?

Reply to
kell

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I emailed you the schematic and posted it to abse as well.
Reply to
John Fields

Still nothing, john.

I managed to scan the schematic that I designed, and touched it up a little. Does it look electrically sound to everyone? I'm pretty sure about the logic, its the transistors I'm worried about. Will a five volt High signal block the current? And if it goes low, will current be allowed to pass? What model of transistor should I get? I calcultae that it will need to provide at least 150 mA at 12v to power the fan, so a >=2W tran. is required. A link to the image that (I hope) works is here:

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Reply to
ghosttwo

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No
Reply to
John Fields

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