High res PWM

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Marcaroni
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High res PWM

Post by Marcaroni » Thu Dec 18, 2008 3:36 pm

Hi.

I'm currently using an RS232 PWM control board from NCD (PWM85 www.controlanything.com). The board takes simple commands via RS232 to control 8 individual channels of PWM output. The problem I'm having is the resolution. It only has 8-bit control...which seems common, so i'm guessing that's fine for most applications. Unfortunately it's just not working for my needs. So my question...is there any way possible to somehow combine two different 8-bit PWM signals into one 16-bit? I realize this sounds awkward, and i'm guessing there is very little chance this is possible, but i've spent hours scouring the internet trying to find an equivalent control board with higher resolution so I'm getting a little desperate.

thanks,
Marcaroni

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Nepo
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Post by Nepo » Thu Jan 01, 2009 2:56 am

I don’t have an answer to your question, but what is it that you’re using PWM to control?

manie
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What about uP

Post by manie » Thu Jan 01, 2009 9:52 am

Can't you use a microprocessor like one of the inexpemsive Picaxe chips ? At 4MHz up to 20KHz PWM and at at 8 MHz double that. From 0% to 100% duty at fixed frequency, unlike the interdependency of the 555 timer where a duty change also changes the frequency. Just a thought.

Marcaroni
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Post by Marcaroni » Fri Jan 02, 2009 4:55 am

Nepo wrote:I don’t have an answer to your question, but what is it that you’re using PWM to control?

these valves:
http://www.sensortechnics.com/index.php ... 1f733a8d26

Marcaroni
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Re: What about uP

Post by Marcaroni » Fri Jan 02, 2009 5:11 am

manie wrote:Can't you use a microprocessor like one of the inexpemsive Picaxe chips ? At 4MHz up to 20KHz PWM and at at 8 MHz double that. From 0% to 100% duty at fixed frequency, unlike the interdependency of the 555 timer where a duty change also changes the frequency. Just a thought.
we probably will end up taking the microprocessor route. we've just been avoiding it in an attempt to use as many off-the-shelf components as possible. we just wanted to try to minimize circuit design and firmware development. we almost pulled it off, but (predictably) we've failed. If NCD's PWM8x board were 16-bit (or better) we'd have pulled it off no problem.
NCD's PWM8x boards have a surprisingly rare feature of being able to sink up to 17amps at 5VDC on the output side, which is why we tried it in our project. The valves we're driving with the board are rated up to 2W, so we could drive those valves with the NCD board as-is. Any other "ready made" PWM seems to be standard 4-20mA.

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