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It's a pretty simple device. I used a PIC flash
microcontroller, RS232 chip, and a dual op-amp to buffer-amplify the signals.
Let me straighten it up a bit and I can post the circuit and code. As of now I
log to the left-over program memory, which is good for > 1000 cycles and
gives about 1 hour logging at 1 sample/sec. This could be improved by 'smart'
logging (only log new data when the data has changed by more than some amount),
or tossing in a serial EEPROM (proabaly best way). Only three connections to the
ET are needed. If there is enough interest we could get a PCB made which is
pretty cheap these days. I would guess total parts cost (w/o enclosure) at about
$30. The only thing it doesn't do now is log charge current - I forgot the
charge current makes the shunt voltage negative (DOH!). Gotta think about
that....
One of main reasons I wanted to do this is to log the battery
voltage during/after charging to keep on eye on battery health. Wish I had done
it earlier,a s I don't knwo how long my charger has been
undercharging...
- SteveS
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