ok, here is my 2" worth.

use a 12C508, it's cheaper than a 555 and all the caps and resisters that go
with it.

now for accuracy. with one resister to an ac power line, or the secondary of
the transformer you have a very stable 60 Hz time base, just count 60 cycles
/ second * 60 seconds / minute * 30 minutes = 108000 cycles. or make the
program easy and use registers for cycles, seconds and minutes.

this is a great first project to learn the pic assembly.

michael

p.s. when you are testing the project, you might want to try setting the
timer to 2 minutes. it will cut down on the debug time.

-----Original Message-----
From: Alex Holden <alex_holden@GEOCITIES.COM>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Tuesday, March 31, 1998 4:32 AM
Subject: Re: Need help with a 30 min. timer.


>Steven Kosmerchock wrote:
>>
>Ever heard of a 555? ;)
>
>>  Hello everybody,
>> I'm new to the world of PIC's.I was wondering if anybody have any
suggestions
> to
>>  help me out. Here's my problem: I need a timer that once activated will
run
> 30
>>  minutes, after the 30 minutes is up a relay will be triggered. Any code,
>>  schematics, or advice would be greatly appreciated. I have the ability
to use
>>  and program these PIC's: 12C509, 12C672, 16F84, 16C63, 14000. Any and
all
>>  comments welcomed. Thanks in advance!!!!!!!!!!!!!!!!!!!!!!!!!!!
>
>--
>------------------- Linux- the choice of a GNU generation.
>--------------------
>: Alex Holden- Caver, Programmer, Land Rover nut, and Radio amateur (M1
>CJD). :
>-------------- http://www.geocities.com/CapeCanaveral/Lab/1532/
>---------------
>