Comments on Ken Shirriff's blog: Secrets of Arduino PWM

I want to use a low frequency PWM, below 10Hz. The...

2012-02-06T22:02:04.383-08:00

I want to use a low frequency PWM, below 10Hz. The frequency isn't critical but would have to be in that area. Any ideas how to get down to that frequency? I want to use the Arduino Uno for other things whilst the PWM is being output.

The version of this article posted at arduino.cc is missing all of the diagrams except the first one.

Thank you very much, this is the best condensed re...

2012-01-19T01:21:23.049-08:00

Thank you very much, this is the best condensed reference I have seen, all clear and to the point!!!

_BV is a macro defined in avr-libc: #define _BV(x...

2011-08-15T00:47:10.254-07:00

_BV is a macro defined in avr-libc:

#define _BV(x) (1 << x)

see http://194.81.104.27/~brian/microprocessor/BVMacro.pdf

This may be a stupid question by a newbie, but wha...

2011-08-14T23:58:42.122-07:00

This may be a stupid question by a newbie, but what is the _BV function? Nowhere to be found in the Arduino reference.

Great summary and guide for using the ATmega328p t...

2011-07-24T14:05:09.521-07:00

Great summary and guide for using the ATmega328p timers! Thanks for taking the time to put this together. Very helpful.

I wrote a brief article on creating PWM using the ...

2011-06-27T08:21:18.401-07:00

I wrote a brief article on creating PWM using the Arduino UNO, with ability to control the frequency on my blog. Just leaving a link here as I found this article very useful in my research !

http://smacula.blogspot.com/2011/04/creating-variable-frequency-pwm-output.html

Very helpful, thanks for your share. As for debug...

2011-05-15T02:56:56.673-07:00

Very helpful, thanks for your share.

As for debugging PWM, I think proteus ISIS is a good tool for that purpose. Proteus has a virtual osilloscope, see my post(in chinese, sorry):
http://coopermaa2nd.blogspot.com/2011/05/proteus-pwm.html

Very informative! Excellent Work! Thanks!

2011-05-01T00:37:39.330-07:00

Very informative! Excellent Work! Thanks!

but how can i get it to make a 38khz freq with 50%...

2011-03-08T14:14:09.448-08:00

but how can i get it to make a 38khz freq with 50% duty cicle?

Thanks for explaining this matter so extensively! ...

2011-02-13T11:47:56.152-08:00

Thanks for explaining this matter so extensively! I was looking for a way to generate 1 MHz on one of the Arduino-pins. Your post helped me a great deal to accomplish that.

The reason I am writing this comment is the following: It took me almost 6 hours till I found out (mainly in sheer desperation) that the order of setting the timer control registers TCCR2* and the output compare registers OCR2* seems to matter! If you assign an OCR before setting the corresponding TCCR the timer simply doesn't start counting.

Colin, thanks for your comment. I'm glad the ...

2010-12-17T22:27:53.023-08:00

Colin, thanks for your comment. I'm glad the article was helpful.

Cassiano, with a sound card oscilloscope, you connect the signal directly to the sound card through a resistor to reduce the current. There are details at http://www.ehow.com/how_2278973_use-sound-card-oscilloscope.html

Most excellent thank you -- saved me days trying t...

2010-12-16T23:44:54.063-08:00

Most excellent thank you -- saved me days trying to make sense of that Atmega328 datasheet
I was using the default 490 Mhz arduino analogWrite PWM and was getting horribly low torque with some small DC motors on low duty cycles. Changed it to 30Hz and now its way better, still runs smooth.

Excellent tutorial Ken. Thanks a lot for sharing y...

2010-09-23T17:55:51.717-07:00

Excellent tutorial Ken. Thanks a lot for sharing your knowledge.

Would you mind elaborating a bit more on how someone could use the sound card and a program such as xoscope to help debug this sort of thing? Do you mean by plugin a speaker to the arduino pin, getting it close to the computer mic and using such a software to graph the wave?

Thanks once again.

that is wonderful.. but whan i was looking at the ...

2010-05-23T01:32:42.218-07:00

that is wonderful.. but whan i was looking at the library i saw in the comments that this will work only for 36-40khz modulation? Whay is that and how can i change it so it will work on 56khz?

Very helpful, thanks--we're trying to use Ardu...

2010-05-22T18:06:03.674-07:00

Very helpful, thanks--we're trying to use Arduinos to power a small pump and measure flow for an open source river modeling system, and I was hung on this topic until reading this--see our stuff at lrrd.blogspot.com.

Ken, I am just learning about Arduino and I have ...

2010-04-21T09:15:45.382-07:00

Ken,

I am just learning about Arduino and I have a question about your article on “Secrets of Arduino PWM”.

Your example says
pinMode(3, OUTPUT);
pinMode(11, OUTPUT);
TCCR2A = _BV(COM2A1) | _BV(COM2B1) | _BV(WGM20);
TCCR2B = _BV(CS22);
OCR2A = 180;
OCR2B = 50;
What I am confused about is previously you stated that that these examples set the clock divisor to 64. Is there a bit inversion in the writes to an AVR register?
Your line TCCR2B = _BV(CS22); would set the TCCR2B register to 00000100b.

Is there something I’m missing here?

Thanks in advance for your response.

Monty

Tom, you asked about how to divide by 64 with the ...

2010-03-16T23:22:38.430-07:00

Tom, you asked about how to divide by 64 with the prescaler. For timer0 and timer1, the clock select bits are set to 011 (CS02,CS01,CS00 or CS12,CS11,CS10). But for timer2, the clock select bits are set to 100 (CS20,CS21,CS20). Confusingly, Timer 2 uses different clock select bit values from Timers 0 and 1.

Excellent article, I've been going through som...

2010-02-27T09:42:48.913-08:00

Excellent article, I've been going through some example code but this made it all come together.

Thanks,
Mike

I am so glad I found this. Just what I needed. ...

2010-02-07T09:56:20.022-08:00

I am so glad I found this. Just what I needed.
One question though-likely I am not understanding some subtlety.
It seems from the datasheet that the 64 pre-scale corresponds to 110. I am wondering if I am missing something, as you mention 100 as the 64 prescale divider.
Thank you!

exactly what I needed! thanks!

2010-01-23T13:38:15.751-08:00

exactly what I needed! thanks!

Excellent paper. Many Thanks

2010-01-10T05:57:13.332-08:00

Excellent paper. Many Thanks

Thank you for the article! As a beginning Arduino...

2009-11-01T10:46:19.917-08:00

Thank you for the article!

As a beginning Arduino user, this is very helpful!