LP filter for converting PWM to DC?

Forum 2005-2010 (read only) General Exhibition
1

Has anyone constructed a low pass filter suitable for converting the PWM signal to DC?
I'd appreciate it if someone could share a schematic or point me to one.

Thanks!

2

So you want to have a constant definable voltage depending on the pwm fequency?

Dont think that would work.

3

I'm trying to use a PWM out to drive an LED and analog panel meter - but a concern I have is that with PWM the needle will bounce on the meter instead of indicating a particular stable DC voltage. I've never used the PWM outs, so I'm not sure either way. I found a snippet somewhere describing a simple lopass filter "smoothing" out the PWM to a relative DC voltage, but I can't find it now...

4

Update - Here's the article I ran across earlier:
http://www.edn.com/article/CA6372821.html

5

I can't help you but I like your Buchla avatar!

6

Why not hook up the meter and see if it bounces? I read the article and thought a little about making a filter with an op-amp, or maybe a passive one with a capacitor and resistor, but the PWM frequency is pretty speedy, so an analog meter might not be fast enough to bounce with it. Not that I'd really know much about it (I was a music major!) Anyway low-pass filters are pretty simple, you can check

cheers,
Collin

7

Yeah in theory it will bounce so fast that it evens its self out.

Alternatively a big capacitor may even it out more.

8

Thanks Cheater/Coldham,

You both reinforced my own suspicion that it may work without any additional circuitry - but I was a little afraid of dropping $40 on the meter until I had a "second opinion". I too had considered just a cap to hope even things out, but that may not even be necessary. In any case, I'll repost with the results once I receive the meter.

Thanks again.
Jason

9

I have just made something similar, and i see no vibrations on the meters and ther are no capicators or filters involed.