Help with ADC conversion

[Darrel Taylor]

I'll second the Comparator idea, but with a little difference. (Don't filter the signal)

Set a timer to have a delay of 20ms or more.
Using the comparator Interrupts, reload that timer every time you get a pulse.

If the voltage drops below the comparator's trigger point, the timer will overflow.
Use the timer interrupt/flag to determine when there's an error condition

<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=3162&stc=1&d=123345227 4" />

[dbachman]

Darrel, Mister_E

I am not very familiar with comparators and the use of timers. I have been trying to read more about how to implement them. But this is what I think I need to do. Feed signal into CCP1 pin (after setting up compare module) on say an 18F1320. Set timer1 to reset after every pulse (half cycle ~8ms) by using comparator interrupt flag. If interrupt flag is not set (voltage below threshhold), timer overflows and sets overflow flag. If this is correct, what I don't understand is where the reference voltage (comparator's trigger point)to determine a low voltage condition comes from. Its probably pretty simple but I haven't grasped it yet.

Thanks for the help,

Don

Edit:
After reading the datasheet again and again and again..... I think I may not have a clue what you guys are trying to tell me...

[mister_e]

That will be hard to setup PIC18F1320 analog comparator, as he don't have any BUT... PIC18F2220 and lots other have some already built-in.

Internal analog comparator works as regular voltage comparator (LM393 and so on), you set a voltage reference on one input pin (voltage divider, trim pot, whatever else fancy stuff), and you apply your signal on the other input pin, then you just monitor the voltage comparator output.

In a PIC, when the output of the comparator change, it can trigger an interrupt event, so it's done in background. Once in the Interrupt handler, you do what you need to do.

Have a look at Darrel's Instant interrupt, this will save you some headaches. There's also some code-example on how to use'em with Timer.
http://www.pbpgroup.com/modules/wfse...p?articleid=19

From there, you should be able to begin some experiments.

[dbachman]

Hey Steve,

I was just check'n to see if you would catch that............not.

Anyway, I do have a couple of 18F2550 which look like they have the analog comparators. After looking at THAT datasheet, things are becoming a little more clear. I think I actually might be able to put something together. Thanks for the help and hopefully you can stand by as I try to get this to work.

Thanks, Don