PWM sounds simple in theory, but...

MarkS

I was trying to dim an LED. It sounds simple. You keep it on, I'm assuming in a loop where you keep outputing a '1', for a certain amount of time and then do the same thing, but turn it off for a certain amount of time and repeat ad nauseum. I couldn't get it to work though. I'm running the PLL at x16, so 80_000_000 = 1 second. That info really does not help too much. If I wanted to dim an LED by x%, what do I do?

MacGeek117

There is a simple PWM object in the Obex (Object Exchange) Look for it in Motor Control.
RoboGeek

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deSilva

There is also a most comprehensive wiki article
propeller.wikispaces.com/PWM

MarkS

deSilva said...
There is also a most comprehensive wiki article
propeller.wikispaces.com/PWM

Thanks!

MarkS

OK, I finally got to try your code (dim_cycle3), but it doesn't work. Is there a trick to it?

deSilva

Perhaps a typo
I don't know, I'll check ..

----
Edit: Yes TWO typos... generally happens when "improving" text without re-checking :-(
Called "Vers 4.0" now
I also added an example in the main routine: Ramp-Up/Ramp down

PUB main | dutyCycle, someStack[noparse][[/noparse]20]
  COGNEW(dim_try3(30, @dutyCycle), @someStack)
   
  REPEAT
    REPEAT WHILE ++dutyCycle <100
      WAITCNT(CNT+CLKFREQ/100)
    REPEAT WHILE --dutyCycle >0
      WAITCNT(CNT+CLKFREQ/100)

Post Edited (deSilva) : 1/1/2008 11:28:12 AM GMT

bulkhead

Is it this line:

onePercentTicks := CLKFREQ/100      ' 100µs = 1% '

where the 100 should be a 10_000?

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I'm new to the propeller!

deSilva

Yes
As you say bulkhead! Improvement to the worse ...
Luckily the comment shows the issue.
I also had a misspelled variable

Drone

In the third line:

onePercentTick > onePercentTicks

right?

BTW - Happy New Year - David

deSilva

:-( Sure! I wanted to improve the "readability"