detecting pwm

Thric

Is there a way to detect whether a pwm signal is present on a pin? Currently I can use timers to find the duty of a PWM signal but if there is no signal present the program will hang indefinitely for an event that will never come. Is there a way to do this without implementing a watchdog?

Phil Pilgrim (PhiPi)

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

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

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

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

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

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

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

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)

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