HP97 The journey begins

[teenix]

Hi all,

I've been playing around with the low battery detect all morning. It has been a bit of a challenge to get the low battery LED to come on when required with the LiPo battery. It has a different voltage vs discharge curve than the old NiCads.

The Spice low battery LED basically has three states - off, partially on, and fully on.

When the LiPo gets near the low battery state, there are only 10's of millivolts change so it is a bit difficult to work with the original circuit. The change in low batt LED indication from partial to fully on is also a few 10's of millivolts. Anyway, I have it about as close as I can get.

I have been writing the user manual, and going over the software as I was writing it to make sure everything works ok. The calculator had a half charged battery and I have had the calculator on and off for the last 4 days. It is still working ok, so a fully charged battery should last for a good amount of time. I connected a 100 ohm resistor across the battery to speed up the discharge and the calculator should work right down to the last bit of charge left in the battery, although I was under the impression that LiPo's should not be completely flattened. The low battery LED should begin to light around the 20-30% remaining charge point.

I have the battery charging via the USB port, so I'll see how that goes. The calculator is still usable during charge.

cheers

Tony