Detecting a pulse

[timmers]

When I worked in Nigeria a few years ago, we employed somebody to start the generator and switch over from utility supply to generator supply. Worked fine, no getting up at 2am like some!

-trouble started when we bought a new generator. We instructed our gen-starter how to check the oil and and where to dip his finger to check the water (couldn't see the level due to the soundproof case).
When we came home later that day, he was busy pouring water into the generator from a watering can. after his second refill I became curious as to why the generator was needing so much water, and there on the top of the case, was the oil filler cap as another 2 gallons disappeared down to the depths of our brand new generator. When I pulled the dipstick out, a spout of water flowed.

After that episode I sacked the gen-starter and I built a PIC based auto starter, which would check the incoming 3 phase for over volts (occaisionaly), under volts (often), one or all phases missing (very common) and then switch over as required. It had a variable brown out facility to prevent reccuring start / stop and control of other variables like cranking time out and cool down runs. It even switched the contactor from utility to local automatically. It used 3x opto couplers to monitor the 3 phases and 3 relays for run, glow & crank.

Worked a treat!

[Dennis]

@trimmers
That definitely is a classic :-)
So the initial code would have been something like

If water_level exist then 
goto sack_gen_starter
else goto use_PIC
end if

Thanks for the info

Dennis

[WOZZY-2010]

Other fun and useful stuff that might be added, with various levels of cost and complexity:

• Log generator run time
• Monitor / Alarm fuel level
• Monitor /Alarm engine or generator winding temperatures
• Count power outage events / Log power out time
• Monitor output power or voltage and current demand
• Auto start periodically to maintain bearings and equipment health...alarm if no start
• etc ...

This is what I love about the versatility of using PIC chips.

[Dennis]

@WOZZY-2010 yes plenty that can be added.
Hardest part would be getting a fuel top up :-)

OK so still no replies regarding a simple IS PULSE EXISTS command ?
I can easily detect zero-crossing but need to know how to check for th
I was thinking of just checking for an absolute minimum pulse using PULSIN or use COUNT since AC has a 50% duty cycle and I would be checking a frequency of 50Hz or 60Hz but how do I set the period to be infinite ?
Using this approach I could say something like WHILE COUNT_VAR > 1

So here are the questions ?

1. Can COUNT period be set to inifinity ?
2. Can COUNT be set to a tight loop to count mains pulses so a variable always stays high so that I could say something like IF COUNT >1 THEN AC EXISTS ?
3. If I used and interrupt on change for every zero-crossing could the interrupt be checked ..something like if interrupt exists then ... or if no interrupt exists then ...

Any thoughts/ideas are welcome ?

Kind regards

Dennis

[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.