SOLVED Need PWM help!!!

Erik765 · Jan 1, 2012

Hello,

I hope this is in the right place, but I've just gone down to Radio Shack and grabbed all the components to throw together LennyRhys' PWM controller from his guide here http://www.overclockers.com/pwm-fan-controller

Anyway, I'm not that great at reading electrical diagrams but thought I did well enough and what I have on my breadboard seems to match after quadruple checking everything. I must be a n00b though 'cause it's not working :bang head

Are the C2's laid out wrong for a series layout?

Here is my layman's drawing to exactly how I have it laid out (since a pic of my actual board probably wouldn't work well):

I REALLY need to get this working to slow down my pump so my water-cooled system isn't as loud as my old air-cooled box which is replaced (and to increase pump life of course).

Can someone (BING??) take a look really quick at this and let me know what may be wrong?

When plugged in to the PSU, the test fan I have runs, but turning the POT doesn't do anything at all

Thanks a ton in advance and please don't laugh if something is blatantly obviously wrong, lol.

z.snafu · Jan 1, 2012

Well..I'm just taking a quick look at this and I've found two errors thus far. If you're using the 555 IC you need 2. You only have one thus far. Error two...if you want the circuit to see the adjustable resistance, you dont use all three terminals in the pot.

z.snafu · Jan 1, 2012

also, some of the terminals on the capacitors are directional, so you need to make sure they're in the right direction.

Erik765 · Jan 1, 2012

Thanks for the reply.

I guess this was the diagram I was going off of:

http://www.overclockers.com/wp-content/uploads/2010/12/PWM-circuit.png

Will it not work with one 555 at all then?

z.snafu · Jan 1, 2012

My bad, the circuit is is being adjust proportionally on the two circuits, so the pot is good

z.snafu · Jan 1, 2012

also, my bad. I was looking at the dual 555 design below the single 555 design

z.snafu · Jan 1, 2012

you dont have pin 1 going to ground

z.snafu · Jan 1, 2012

pin 4 isnt going to pin 8

z.snafu · Jan 1, 2012

pin 6 isnt going to your c2 cluster

Erik765 · Jan 1, 2012

I've managed to get it working somewhat. Although I suspect it is not 100% correct as I can get the speed to lower but, while moving the POT, the speed suddenly drops (about right in the middle of the range). I can find a middle medium speed by slightly moving the POT, but it's a pretty small area of it.

I ended up tearing it down and re-wiring it on the breadboard.

The strange part is, it only works when the D1 is removed from the diagram altogether. If I put it back in, the fan just runs at lowest speed.

z.snafu · Jan 1, 2012

post a pic of your board from above so I can see what's going on once you get it rebuilt.

Erik765 · Jan 2, 2012

Thanks again for your help.

Here are a couple pics of the latest build.

Again, it only works if I remove D2 (not D1 sorry). The one that is connected to pin 1 of the ic.

As a reference, the Caps with the black dots on top are C2 in parallel.

I don't mind going with it without D2 if it's not gonna hurt anything in the end. although the POT is a little touchy and only a really small portion of it is usable to adjust the speed. It drops (or raises) really fast.

z.snafu · Jan 2, 2012

ok i'm looking over it now, it could be a time consuming processes. do you want me to post the errors i find as i see them, or would you rather me compile a list of them all and post?

also, dont get discouraged, this is really tedious. I remember when i first started in my EE labs

Erik765 · Jan 2, 2012

I won't get discouraged, I've spent all day on it so if that was gonna happen, it would have long ago, lol.

I just appreciate your help.

All at once or as you see them, either way really.

Thanks again. Much appreciated.

z.snafu · Jan 2, 2012

big points - move the pot and diode connections on rows 10 and 12 to separate rows. any row will do, just make sure no other components are wired to that row. remove the tiny jumper that's connected to both sides of the capacitor connected to the pot. that shorts it out, basically the circuit won't see it.

z.snafu · Jan 2, 2012

and the 5v source should be connected to pin 8 in case your not already doing that (but that could just not be shown in the circuit).

z.snafu · Jan 2, 2012

oh, and as a reminder that to add capacitances place them in parallel, to get a smaller value (ie 1/c1+1/c2) place them in series. it looks like they're in parallel now

z.snafu · Jan 2, 2012

basic rule - anything you connect to both pins of the same part is in parallel. unless you explicitly want this, watch out for it. for example, the jumper going between two pints on that capacitor, or that capacitor that is connected to vcc on both pins... that totally alters how the circuit sees those parts (or in this case, doesnt see them)

z.snafu · Jan 2, 2012

ah wait
i saw that second cap wrong, so its just the one with the jumper

Erik765 · Jan 2, 2012

Wow, pretty obvious once i look at it, lol.

Thanks for not laughing yet!

SOLVED Need PWM help!!!

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