[PD] OT: PWM frequency of Arduino

[Martin Peach]

>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.

Martin