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### Topic: Silencing audiable PWM signals (Read 1 time)previous topic - next topic

#### physic.dude

##### Nov 20, 2012, 05:10 amLast Edit: Nov 20, 2012, 07:31 am by physics-dude Reason: 1
I have this hefty 12 volt fan that has its speed regulated via PWM. It buzzes very loudly when in use and I wish to silence it.
A simple 25v 10uF capacitor on the fan's input lessons the sound slightly. An increase in capacitance lessons the sound more, but limits the range in speed control for the fan. (i.e. 50% duity cycle and up shows no change in the speed for the fan.)

The PWM frequency is 76Hz.
Finally, some brief specs on the fan are:
- Voltage range = 7.0 - 13.8
- Current = 710mA
- Input = 8.52w

Changing the supplied PWM frequency is not one of my options at this time.

#### retrolefty

#1
##### Nov 20, 2012, 05:14 am
Quote
Changing the supplied PWM frequency is not one of my options at this time.

Then you will most likely just have to learn to live with the sound. Changing PWM frequency is probably the solution required, unless you wish to convert to pure analog voltage control via a heatsinked power transistor(s) operating in it's linear range.

Lefty

#### dhenry

#2
##### Nov 20, 2012, 01:10 pm
Lower the pwm frequency.

#### runaway_pancake

#3
##### Nov 20, 2012, 01:53 pm

Changing the supplied PWM frequency is not one of my options at this time.

Lower the pwm frequency.

"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

#### John_S

#4
##### Nov 20, 2012, 06:22 pm
Your post doesn't say if your source of the PWM is an arduino, or even if an arduino is involved here.
If you have a spare arduino lying around (or attiny), you could feed the source of the 76Hz PWM through a low pass filter into an analog input. Set an output PWM proportional to the input at a frequency of your choice.

Problem solved with minimal parts.

#### physic.dude

#5
##### Nov 20, 2012, 08:13 pmLast Edit: Nov 22, 2012, 09:47 am by physics-dude Reason: 1

Your post doesn't say if your source of the PWM is an arduino, or even if an arduino is involved here.

The source of the PWM is the Melzi electronics on my new RepRap. The whole system is based off the Arduino Leonardo and utilizes the ATMEGA644P.

Edit: I got everything working just fine now thanks in part to users on the RepRap forums.
I forgot to mention here that I had a 12v regulator between the 19v Melzi electronics and fan. The first couple I was using weren't quite in spec, but these new ones,  NJM7812FA, work like a charm. With that, the only other thing I included was a 35v 100uF cap on the fan's input.

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