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elcray
11-28-2007, 03:35 PM
I have a project where I have interfaced a Duratrax Electronic Speed Control to a Phidgets servo control, to operate a 12V DC brushless fan. That works fine, but my question rests on sensing the Fan speed. The fan I am using (4715KL-04W-B56) I believe, transmits a PWM signal via one of the extra leads that relates to speed (RPM). Any ideas how to read this with my 8/8/8 interface kit?

Alex
11-29-2007, 10:57 AM
Hey elcray!

Do you happen to have a link to the speed controller product page and any docs/datasheets?

elcray
11-29-2007, 03:41 PM
Hey elcray!

Do you happen to have a link to the speed controller product page and any docs/datasheets?

The speed controller is a cheap Duratrax instellisense, but the item I have in question is the signal from the fan. Unfortunately, I can't find a spec from the mfg of the fan that shows anything about the leads; other than red and black +/- dc power; which, I think I could have figured out myself ;->

Dave
12-04-2007, 03:01 PM
Chances are kind of slim that you'll be able to read that PWM with the 8/8/8, because of its slow sample rate. The 8/8/8's digital inputs only sample at 125 Hz, and your PWM frequency would have to be far lower than that to get an accurate reading.

You may be able to get a rough measurement by low-pass filtering the PWM signal and feeding the result into an analog input.

kdwyer
12-04-2007, 04:34 PM
Maybe if you change what you want to sense...
If sensing fan speed seems un-do-able, maybe measuring analog voltage would give you an approximation you could work with.
Sometimes a 'quick 'n dirty' solution is the only solution.

elcray
12-05-2007, 10:38 AM
Chances are kind of slim that you'll be able to read that PWM with the 8/8/8, because of its slow sample rate. The 8/8/8's digital inputs only sample at 125 Hz, and your PWM frequency would have to be far lower than that to get an accurate reading.

You may be able to get a rough measurement by low-pass filtering the PWM signal and feeding the result into an analog input.

Thanks. That's kind of what I expected, but just wanted to be sure.


Maybe if you change what you want to sense...
If sensing fan speed seems un-do-able, maybe measuring analog voltage would give you an approximation you could work with.
Sometimes a 'quick 'n dirty' solution is the only solution.

That might be possible. All I'm really trying to accomplish is to make sure that something isn't blocking the fan from turning. I might hit that from a different direction.

Thanks all for the feedback.