[sdiy] PWM, Vactrols & Opto-Isolators

[Dustin Withers]

I'll have to go over this reply a few times. Thanks everyone for the
input. I think I'll be ordering an Aruduino Mega off of Amazon later
as a friend gave me a $75 gift card. I mean really what else should I
buy from Amazon? ;)

-dustin

On Sat, Jan 16, 2010 at 4:19 PM, cheater cheater <cheater00 at gmail.com> wrote:
> Dustin,
> a simple RC filter is going to be good enough and much cheaper than an
> opto based design. The frequency of the PWM is constant and you can
> tune the filter to it. Bear in mind that the concept of recovering the
> duty cycle value from a general PWM signal is very different from
> making a DAC out of a PWM driver.
>
> An opto coupler won't give you perfect quality as it has lots of
> non-linearities. Also remember that a diode's 'brightness' can be
> controlled by PWM not because of the nature of the diode, but because
> of the nature of our eyes, which are not quick enough to see the
> blinking. A nightfly would see the blinking just too well. And your
> circuit would 'se' the blinking too.
>
> An opto coupler geared to digital coupling can be used for a crude
> form of PWM: full-wave rectify your signal, and use that as input into
> the opto. Use the output to turn the original signal on and off. You
> change the duty cycle by dc-offset on the opto's input. Mind you, you
> could use a diode just as well, but it would sound just a slight
> different.
>
>
>> Most of the things I'm up to are pretty boring compared to the rest of
>> what some of you are doing :)
>
> I've been sleeping all day today. There's no way you had a more boring
> way than I have :P
>
> D.
>
> On Thu, Jan 14, 2010 at 02:42, Dustin Withers <fadeddata at gmail.com> wrote:
>> Jason,
>>
>> Thanks for that. I'll be sure to check it out.
>>
>> -dustin
>>
>> On Wed, Jan 13, 2010 at 7:14 PM, Jason Proctor <jason at redfish.net> wrote:
>>> ymmv, but i gave up on the pwm output option and use an SPI DAC instead
>>> (TLV5618). straightforward to use and works like a champ.
>>>
>>> code and circuits etc in the files section of arduino_synth @yahoo.
>>>
>>>
>>>
>>>> The application is a mix of my own interest and that I've noticed many
>>>> of these inexpensive micro controller boards have many PWM outs. I'd
>>>> like to be able to do digital control of analog circuits. It seems my
>>>> best bet maybe some kind of DAC though, right?
>>>>
>>>> dustin
>>>>
>>>> On Wed, Jan 13, 2010 at 5:37 PM, Tom Wiltshire <tom at electricdruid.net>
>>>> wrote:
>>>>>
>>>>>  Dustin,
>>>>>
>>>>>  If you're looking to get a DC level out, then I'd say, yes, 30KHz is
>>>>> high.
>>>>>  You could set the RC filter frequency for 10Hz and the pulses would be
>>>>> more
>>>>>  than 3 decades above the cutoff, which ought to give a decent filtering
>>>>>  action even with such a simple layout.
>>>>>
>>>>>  Jay's comment's about linearity are very pertinent though. PWM->LED
>>>>>  linearity isn't going to be perfect, and LED->LDR linearity will add
>>>>> it's
>>>>>  own twist too. How accurate do you need it? What's the application?
>>>>>
>>>>>  Regards,
>>>>>  Tom
>>>>>
>>>>>
>>>>>  On 13 Jan 2010, at 19:03, Dustin Withers wrote:
>>>>>
>>>>>>  Tom,
>>>>>>
>>>>>>  Is a pulse frequency of 30Khz considered high?
>>>>>>
>>>>>>  Thanks for the help,
>>>>>>  -dustin
>>>>>
>>>>>
>>>> _______________________________________________
>>>> Synth-diy mailing list
>>>> Synth-diy at dropmix.xs4all.nl
>>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>>
>>> _______________________________________________
>>> Synth-diy mailing list
>>> Synth-diy at dropmix.xs4all.nl
>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>>
>>
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>
>