Detecting a pulse

[Charles Linquis]

Again - I don't know what else your PIC must do at the same time, but PULSIN and COUNT are generally bad, since your code can do NOTHING ELSE during the count interval.

If that is the case just do something like:

  CLEAR

Topp:

   IF  InputPin = 0 THEN
        Counter = 0
   ENDIF

   IF Counter > 2 then goto PowerGone   
   IF Counter < 254 THEN Counter = Counter + 1
   Pause 5
   Goto Topp


PowerGone:
   HSEROUT ["Turn on the Generator"]
   Pause 10
   END

[Dennis]

@Charles

Thanks very much for both replies and apologies for not replying tot he first one, I think for some reason I got sidetracked after reading it (it suddenly got some thoughts going) and I forgot to reply :-(

Regarding the latest posting you have made... what exactly do you have in mind with this code ?

IF  InputPin = 0 THEN
        Counter = 0
   ENDIF

   IF Counter > 2 then goto PowerGone   
   IF Counter < 254 THEN Counter = Counter + 1
   Pause 5
   Goto Topp

Are you suggesting I have a zero-cross detector on 'InputPin' ?

And Counter > 2 ?
What are we counting ?


Kind regards
Dennis

[Charles Linquis]

There are dozens of ways to do this, but in this case, I'm referring to the circuit that I described earlier - an optoisolator. The input pin in my code would be connected to the collector of the phototransistor in the optocoupler. If you build the circuit I described, you will find that the output of the opto is a square wave, with a period equal to the period of your AC (60 Hz = 16.666 ms, 50Hz = 20 ms). The output will be low for one half-cycle (8.3ms or 10 ms) and high for the other half-cycle. The low-to-high and high-to-low transitions will occur on the zero-crossings of the AC. The circuit only detects "positive" half-cycles.

The counter increments every 5 msec, but if a half cycle comes along, the counter gets cleared (because the pin is low), and the count never gets above 2. If a positive half-cycle is missing, the counter increments to 3 and you get an indication that your power is gone.



PULSIN and COUNT are sometimes called "blocking" commands because between the invocation of the command and the timeout, the code can do nothing else. I generally avoid them at all costs.

[Dennis]

@ Charles

Once again thanks for the reply ...!

Will feedback once I have something functional :-)

Kind regards

Dennis