I did a simple NiMH charger for a veterinary thermometer. The thermometer
has a 5 cell NiMH pack in it. It charges with a 12VDC "wall wart" power
supply. Because I already used an LTC regulator in the device, I used
another one as a charger switch (set feedback input voltage to zero so the
regulator just saturates when enabled). I use a resistor between the
incoming DC and the switch, which then drives the battery. Not quite
constant current charging, but close enough. During charging, a PIC
watches the battery voltage. If it stops rising for a few minutes, I
assume the battery is charged and turn off the charger. If the battery
voltage falls below some threshold, I start the charge cycle again. This
is "zero delta V charge termination." The PIC handling the charger is the
same one that does everything else.

I'm currently working on another project that requires charging of two AAA
cells from the AC line. I've decided to just use an external charger
(http://www.powerstream.com/NiMHWMm.htm) for this one.

Harold




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