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.
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.