[PD] Re: [PD-announce] PWM in Pd

Hans-Christoph Steiner hans at eds.org
Fri May 26 13:17:19 CEST 2006


I just realized the answer to my question about getting positive-only  
voltages from the sound card.  The DC filters will probably remove  
the DC offset, therefore, the output voltage on a PWM signal will  
also be centered again on 0, and therefore swing from negative to  
positive.  I do remember getting some very low frequencies out of a  
computer when testing speakers.  But I haven't actually tested this  
[pwm~] object for electronics.  But it would be nice to have a very  
well implemented [pwm~], so its great that this discussion happened.

I did use the [pwm] object with a MIDI-controlled relay box, worked  
quite well at 30-60Hz on a biggish DC motor.

.hc

On May 26, 2006, at 11:39 AM, padawan12 wrote:

>
> Very true. The DC blockers in most s/c are going to be limiting.
> But there's no reason to assume people using Pd for more serious
> experimental applications won't use correct DAC hardware. I think
> its very exciting to see the emergence of Pd as an application
> for wider research in engineering, rapid prototyping etc and I
> applaud HC for thoroughness and attention to detail in the code.
> The beauty of sw over hw is extensibility, on a 64 bit system
> you could use this to position a radio telescope or whatever, far
> beyond the grain you'd ever get with 7bit microcontrollers.
>
>
> On Thu, 25 May 2006 13:24:16 -0400
> Martin Peach <martinrp at alcor.concordia.ca> wrote:
>
>> Hans-Christoph Steiner wrote:
>>> I should say, I forgot that PWM was used in synthesis some, so I was
>>> thinking about electronics and control when I was talking about PWM.
>>> That's why my PWM objects are tailored towards, but should work  
>>> fine  in
>>> the audio context too, unless you need the wandering DC offset.
>>
>> For controlling things with PWM I think you'll need to modify your  
>> sound
>> card if you want DC output. AFAIK they all have capacitors on the  
>> ouput
>> to block DC. I find it easier to program a PIC to do the PWM and  
>> talk to
>> it from PD using MIDI continuous controller messages for 14-bit
>> resolution, or noteon with velocity meaning pulsewidth for 7-bits.
>>
>> Martin
>>
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                                            - Dr. Martin Luther King,  
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