[PD] OT: PWM frequency of Arduino

Hans-Christoph Steiner hans at eds.org
Fri Sep 12 22:02:09 CEST 2008

On Sep 11, 2008, at 3:59 PM, Martin Peach wrote:

>> From: Derek Holzer <derek at umatic.nl>
>> To: pd-list at iem.at
>> Subject: [PD] OT: PWM frequency of Arduino
>> Date: Thu, 11 Sep 2008 21:09:33 +0200
>> Hi all,
>> using Pduino as a CV generator for my modular. First problem is to  
>> make
>> a low pass filter circuit to remove the PWM noise and get smooth  
>> DC out.
>> Might be helpful to know the default PWM frequency. I know it's  
>> set in
>> the firmware, but I've read everything from 450 Hz to 32 Khz, and
>> several other numbers in between out there in Googleland. I'm using
>> Arduino 0011 and the Arduino NG board (ATMega8 controller). Anyone  
>> have
>> the definitive answer?
> The atmega168 data sheet gives the frequency for Timer1 in  phase- 
> correct
> pwm mode as
> fclk_I/O/(2*N*TOP)
> where N is prescaler (set to 64 in init() in wiring.c), TOP is set  
> to 255 in
> init() in wiring.c, and fclk_I/O is equal to the crystal frequency
> (16000000), so it should be about 490.2Hz. (I have a motor  
> connected to it
> now and it sounds about that pitch at low duty cycles.)
> On the atmega168, Timer0 is used in fast pwm mode and runs at twice  
> that
> frequency.

I have 30kHz burned in my brain, but I don't have a reference.

You could try setting the PWM at 50% duty cycle, hooking it up via  
big capacitor (to filter the DC) to a speaker.  Then compare the  
sound to a square wave generated by Pd.


> Martin
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