Re: TI-H: More AVR Qs

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Re: TI-H: More AVR Qs


From: Grant Stockly <gussie@stockly.com>
> >Would the internal RC clock get me that kind of accuracy (withing a
couple
> >of seconds a month)?
>
> If you keep the temperature of the AVR THE SAME.

Do you have any idea how much the clock speed would vary by between about 70
and 90 degrees F?  If the variance is reasonably low I can probably deal
with it.  Even it isn't low, I could plot it and include a table to correct
for it (there will be a temp sensor on the device, so I could use the
current temp to look up the ticks/second value and use that to more
accurately determine the correct delay time).  I've got plenty of code
space, and physical is a premium, so it wouldn't be a big problem.  Anyway,
I haven't decided yet, a crystal might be the simplest.

Also, I think I can do away with the external memory for the basic model,
the 64 bytes of EEPROM is big enough to store 60 hours worth of info if I
compress the temperature data into 4 bit blocks. I can scale to 2 degree
increments (thats as accurate as the temp sensor is anyway) over a 32 degree
range and have 4 bit data.  If the temp goes outside of the 32 degree range,
I can just wrap it around.  The computer program that displays the data can
examine the rate of change and detect wrap-arounds so it can correctly
display the data.
With two bytes I can store a head and tail pointer and use the EEPROM as a
circular buffer, so even if the user doesn't download the data after 60
hours, it will continue to log, just maintaining the prior 60 hours worth of
data.

Currently I'm trying to use the programmer from the BA1FB site, apparently a
serial programmer that connects to the computers parallel port.  Are there
any parallel programmers that connect the same way (of course they would
require a 12v source too)?

If not I'll see about writing one that just sets that RC enable bit.  Then I
can just program it in serial mode and then set the bit in parallel mode.

What is Marshall's web site?  I'd like to request some samples.

Thanks
DK
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