On Thu, Nov 22, 2001 at 09:26:28PM +1300, Jinx wrote:
> If you really want low-cost you can do the whole thing with just
> the PIC
>
> http://home.clear.net.nz/pages/joecolquitt/0wdttemp.html
>
> The F84 has 64 bytes EEPROM/68 RAM,  F628 has 128/224. Not
> much compared to the 8k of a 24C65 though. How often do you
> want to take readings ? The alternative would be to use one of the
> other more recent PICs in the F8xx that can write to program memory.
> I haven't done this but think that you can use this method for data
> storage. If that's wrong (haven't got an F8xx manual handy) I'm sure
> we'll be put straight

You're right on point Jinx. The F8xx parts can programmatically write their
program memory.

I happend to be a fan on the DS1620 as I'm using it in my current thermostat.
The only caution I'd like to add is that they are sensitive little buggers.
When I was doing my initial testing they'd always read with a higher temp
than ambient. It turns out that the miniscule heat given off the other IC's
on the board was raising the temp on the 1620 high enough to change its
reading. I ended up moving it to the edge of the board where it reads more
accurately.

Another relatively inexpensive option is to use a LM34 or LM35 temp sensor
and the A/D and programmable program memory of an 8XX part. Something like
a 16F876 may be appropriate.

But it should be an easily doable project no matter which path you choose.
If you choose the DS162X parts then I have a complete application that
reads, converts, and displays temp in Fahrenheit. Only the logging and
serial routines are missing.

BAJ

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