Variable frequency output

Captain Blammo · 2005-01-23 07:34

I'd like to make an LED flash at a rate controlled by a couple of pots (one for frequency, the other for pulse width), but I've got a bit stuck on how to accomplish this with a BS2SX.

I'd just use FREQOUT, but it seems that it generates a sine wave, where I'd really want a square wave. The PWM command doesn't give you neatly divided on/off time, so that's out. If I was going to use a fixed pulse width, I could just use PAUSE and PULSOUT, though this would still limit me to around 1kHz maximum.

So I suppose my question is: How do you generate a square wave with easy-to-specify frequency and pulse width? Is there an easy way that I don't know about?

Thanks for any help!

CB

Bean · 2005-01-23 14:19

What frequency range do you want to pulse at ?
Bean.

Captain Blammo · 2005-01-23 16:29

1-1000Hz would be fine, though the higher I can set it the better. The real problem with using PAUSE and PULSOUT is that changing the pulse width will affect the frequency, which I don't want to happen.

Bean · 2005-01-23 19:07

I don't see how you can do that with just the stamp.

Take a look at the PWMPAL chip from parallax.

http://www.parallax.com/detail.asp?product_id=28020

Or you could do it with the SX chip and SX/B, but you would need the SX-Key programmer.

Bean.
·

Jim McCorison · 2005-01-23 19:41

CB,

My brain is a little sleepy from an all-you-can-eat pancake feed this morning, so maybe I'm not catching what you are trying to do. But.. I think the following is what you describe

freq    var   byte      ' The full wave frequency
width   var   byte      ' The width of the on pulse
fudge   var   nib       ' Fudge to account for execution times
led     PIN  1          ' I/O pin for the LED

do
  led = 1
  pause width
  led = 0
  pause freq - width - fudge
loop

Fudge is used to compensate for the execution overhead in the loop. Depending on how accurate the timing needs to be you'll have to twiddle fudge to make the loop come out right. But once set you shouldn't have to change it unless you move it to another model of stamp.

Jim

added: Obviosuly the above is just a control snippet. You've have to work in getting the pot settings and their affect on the timing loop, etc.

Post Edited (Jim McCorison) : 1/23/2005 7:48:03 PM GMT

Variable frequency output

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