PWM to Analog converter circuit

Subliminal Aura said:
You know that just flew over my head don't you :D Wish I had your skills, I would be building all the time.

Here's one for you that I'm sure you'll enjoy .... You're next project should be to extend this such that the fans illuminate to a colour that indicates how fast they're going !

red > amber > green :eek: have fun mate :)
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That's easy.

PWM > low pass filter > comparator > some logic gates > link to transistor > 3 sets of led on fan circumference. I've done 12 LEDs on a fan before so this would be an evolution.

The low pass filter normalises the 0-5v pwm to a steady voltage. The comparator would check that voltage against its reference and when it goes high it would trigger a led. The logic gate would prevent all LEDs lighting up.

Would I do it though? Probably not.

I have created a very small circuit for Panyan that adjusted led brightness based on PWM. Look back through the thread. That was for a led strip. Not sure if he ever used it though. Worked a bewt though ;)

Btw check the led sequencer link in my sig if you like led fans.


Back in topic now I think.
 
Subliminal Aura said:
You Sir are a genius..... THANK YOU :)

Only tweaks I made were to loosen the pot - I was surprised that it took quite a few rotations so can only guess that it is very granular. Am I also right in thinking that the current shouldn't exceed 0.5Amps and I measure it via the molex +/- end point using a voltmeter ?

Big thank you and I sincerely hope you keep this project alive :)

EDIT: Fine tuning - I found that modifying the pot whilst at full rpm best for determining the levels :)
Click to expand...

Thank you.

Those Pots are 20 turn 50k Ohm 0.5W rather than the 3/4 turn ones you normally get, which are rated at 0.15W and therefore not good for high current use.

Even though the pots are linear while in this circuit the pots work in a logarithmic fashion and at the higher power end you need to turn it only slightly to get a comparitively high change in output power. At the one or two fan end of the spectrum it can take a few turns to get the sweet spot. :)
 
Mine goes down to around 550 and then either shows zero or sometimes it picks up the PWM frequency of 20-25kHz. It's just one of those things.

As the voltage of a dc fan decreases the signal current it sends back to the tach circuit on the motherboard decreases with it. Eventually the motherboard will not be sensitive enough to read it, or it will start seeing the PWM pulses as a stronger signal.

Not sure if it happens with a true PWM fan so could just be a feature of the way the circuit works.
 
Finally got some of these puppies in.

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They fit reasonably well to the board. Haven't tried one yet on the transistor but hopefully it'll work out well.

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On another subject I've been contacted by two hotmail users via trust but have received no reply back. If you are one of those check your email.
 
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I've been thinking about LEDs again recently and how I can get them onto the converter to make it more interesting, at least for me anyway as my converter is semi visible at the top front of my case.

Thinking along the lines of a spindicator...


...but using some junkbox parts rather than expensive micros.

Along the same lines as my spinning LED fan mod from a couple of years ago but without the persistence and running off the fan RPM tach.

Might have a quick fiddle about with this over the weekend on my breadboard.



In other news I'm looking to etch my own PCBs. I've already drafted out the circuit ready for toner transfer and SMD resistors, if I decide to go down that route rather than through hole. I should probably make one suitable for through hole as well as I have loads of the things :) If I etch my own they will be more professional, easier to build and make them less prone to circuit mistakes as you get with veroboard. I could even make kits for folk who fancy a bit of soldering themselves.

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I'm getting an old oscilloscope later in the month so I will be able to actually visualise the output of the converter properly at last rather than guessing.
 
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Just thought I'd throw in an update as I just got my first oscilloscope.

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A 40MHz old analog Advance Gould oscilloscope.

I recorded a short-ish video of how the voltage looks in real time as it reacts to the PWM converter and basically what the PWM signal looks like. I also threw a resistor on there and tried a couple of caps out to see what difference it makes.


I always thought the circuit was robust and safe for use and this confirms it. No nasty spikes, no back emf, just a nice smooth voltage running to the fan.
 
Thanks guys.

Here's an interesting one. Developed from this blueprint.

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A GPU controlled converter with separate PWM output for the converter fan, pass through for GPU fan and a free tach wire for future tach hookup.

Looks a bit like this.

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Works great on the oscilloscope too. 4 pin PWm connector fitted to the yellow tach wire as I just don't have any 3 pin connectors. Probably should get some :/

This one is for Lil-Diabo. :)

I wonder how many of these things I've made now.
 
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I call it a feature :)

It happens when you drive the fans a touch on the slow side. PWM fans are generally limited to around 600-700RPM as a minimum speed and this is electronically prevented from going lower. There is no such device in a 3 pin fan. I'm not even sure what the device or sub-circuit would be as I've never really looked into it.
 
Lettuce...

The converters can easily be hidden behind the motherboard, tucked into a drive bay or something. The board dimensions are around 70x20x20mm. I usually throw a few hundred mm of cable on the end to give flexibility.

It will act like a PWM fan once you tweak using the potentiometer to set the response but this is just a single time thing unless you add or remove fans.

CraigRobbo...

Sounds interesting. I've looked into PCB etching and have etched one or two boards (badly) but to be honest the difference in size wasn't that great as the fan headers take a lot of room, as does the transistor heatsink. Might be worth a little more effort and SMD components though.
 
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I wouldn't have wiring in between cards like that unless you can help it. Better solution would be to have the PWM connector on the card go around the back where the converter is hidden, then the fan wiring gets hooked up to it there.

If the PWM converter PCB doesn't have a heatsink it might fit ok but it would run a touch on the warm side but would still probably be ok for the Gelid fans. The transistor gets warm once you start adding more and more fans. I can also minimise the height by using a fan connector on a wire rather than on board like most I make. There have been several I've made with connectors off board.
 
Yes mate I could look into right angle connectors. I could put three 3 ways in a row without much difficulty. I did have some kicking about too but straightened them into straight headers :)
 
So I'm making 2 converters for Dockie.

These look awesome and the neatest I've ever done I think. These support four fans each.

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New veroboard with white lines and some underside resistor soldering leave the topside looking quite neat.

With heatsinks fitted...

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These two board will be linked together to a single PWM and a single Molex for power, although I will be throwing an additional fan tach out in for the second board.
 
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Here's one destined to control the fans on a Gelid Icy Vision. PH series connectors at both ends so plugs into graphics card, snakes off behind the motherboard and then comes back to the card for the fan plugging.

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And I've added the wiring to the other one. Both these puppies work great as usual. Just needs its heatshrink now.

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Here's one of the GPU ones all dressed up.

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And for no particular reason I made a video.

 
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Just to let you know Lettuce and Dockie your converters are all packaged up and next to my front door ready for the Mrs to take to the Post Office. Hopefully she'll get the chance today.
 
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