detecting pwm

Comments

• Phil Pilgrim (PhiPi) Posts: 23,514

  2012-08-24 20:21 edited 2012-08-24 20:21

  Sure. Set up a counter to count when there are transitions on the pin (low-to-high is mode %01010). Check its phase register periodically for activity.
  
  -Phil
• Duane Degn Posts: 10,588

  2012-08-24 20:31 edited 2012-08-24 20:31

  You don't have to use a "waitpxx" command to check for pin states. Some quadrature encoder programs just keep checking pin states and compares the new pin state with the previous state to see if it has changed.
• Thric Posts: 109

  2012-08-25 20:47 edited 2012-08-25 20:47

  So I did some much needed reading in the manual as well as around the forums and i came up with this code
  

  PUB Pulse_detect(Pin) 
  
    DIRA[pin]~
    ctra := 0
    ctra[30..26] := %01010        ' set up counter for positive edge detection
    ctra[5..0] := Pin
    frqa := 1
    waitcnt(10_000+cnt)
    if phsa > 0
      ctra :=0
      return 1
    else
      ctra :=0
      return 0  
                   
  

  
  Problem is it doesn't seem to be working as I would expect it too (of course). See any blatantly obvious mistakes?
• kuroneko Posts: 3,623

  2012-08-25 20:56 edited 2012-08-25 20:56

  Thric wrote: »

  Problem is it doesn't seem to be working as I would expect it too (of course). See any blatantly obvious mistakes?

  Can you describe the problem you're (still) having? The only thing I can see which would have an impact is that you don't reset phsa. Try something like

  PUB Pulse_detect(Pin) 
  
    DIRA[pin]~
    ctra[30..26] := %01010        ' set up counter for positive edge detection
    ctra[5..0] := Pin
    frqa := 1
    waitcnt(10_000+cnt)
    ctra := 0
    if phsa[COLOR="#FF0000"]~[/COLOR]
      return 1
  
  [COLOR="silver"]' implied return 0 otherwise[/COLOR]
  

  Or reset phsa before waiting. Your choice.
  
  Following my own advice here, since frqa stays not equal zero you should clear phsa once the counter is upset:

  PUB Pulse_detect(Pin) 
  
    DIRA[pin]~
    ctra[30..26] := %01010        ' set up counter for positive edge detection
    ctra[5..0] := Pin
    frqa := 1
    phsa := 0
    waitcnt(10_000+cnt)
    ctra := 0
    if phsa
      return 1
  
  [COLOR="silver"]' implied return 0 otherwise[/COLOR]
  
• Thric Posts: 109

  2012-08-25 21:08 edited 2012-08-25 21:08

  Alright I found my problem... simple of course. I just needed to wait longer, I just chose an arbitrary value but I should calculate it out to find the smallest number. Thanks for the help
  
  Edit: maybe i jumped the gun a bit for no problems, works one minute and not the next. I'll check latter.
• Thric Posts: 109

  2012-08-25 21:35 edited 2012-08-25 21:35

  Alright so I figured out the problem (finally). The counter is working but the only problem is that the pins I'm testing are all floating, but when pulled to ground the program performs as expected. There must be some software method of pulling a pin to ground right?
• kuroneko Posts: 3,623

  2012-08-25 21:44 edited 2012-08-25 21:44

  Thric wrote: »

  There must be some software method of pulling a pin to ground right?

  You could define it as an output but that would work against whatever external h/w you're trying to monitor. What's wrong with ordinary pull-ups?
• Mark_T Posts: 1,981

  2012-08-26 04:57 edited 2012-08-26 04:57

  kuroneko wrote: »

  You could define it as an output but that would work against whatever external h/w you're trying to monitor. What's wrong with ordinary pull-ups?

  
  Adds to the BOM...
• Phil Pilgrim (PhiPi) Posts: 23,514

  2012-08-26 10:59 edited 2012-08-26 10:59

  Mark_T wrote:

  Adds to the BOM...

  
  Here ya go: 20,000 pull-up resistors for $37.05. That's less than two-tenths of a cent apiece.
  
  -Phil