Hi,
  After having yet another NiMH charger die on me (at least this one gave me
a firework display before it gave up), I started thinking... what about
building a battery charger... The question turned to "What should I use to
control it" - the answer inevitably ended up being "a PIC".

  Has anyone built an "intelligent" NiMH charger out of a PIC? What I'm
thinking about building is something with these specs:

  - Reflex (aka burp, negative pulse, ...) and Constant Current Fast charging
  - Charge current variable from 50mA to 2A
  - Discharge pulse current variable from 100mA to 5A
  - Timing variable from 30 minutes to 8 hours
  - Onboard voltage-vs-time data log (I need an excuse to use one of those
    FRAM chips that's been cluttering my junkbox for ages)
  - Charges 1 to 4 NiMH cells
  - PC link to download data log, view charger status, upgrade firmware and
    tweak algorithm timing
  - 16x2 LCD display

  As far as current regulation goes, I was going to use an opamp with a
push-pull driver stage to do both charging and discharging. A DAC will be
used to produce a +/- 2.048V signal that'll be fed to the opamp to select the
charge/discharge voltage.

  What I'm thinking about is something along the lines of an ICS1702, but
implemented in a far more versatile way... That said, it seems Galaxy Power
have vanished, so ICS1702s might be a little hard to get anyway...

  Anyone got any comments on this? Is it worth bothering implementing Reflex
charging, or should I just stick to constant-current with voltage-delta
termination?

  Yes, I know this could potentially turn into a REALLY expensive project,
but I've had two chargers die recently, and I'm sick of spending good money
on something I'm not even sure is charging the batteries properly... At least
if I build my own, I get to play with the algorithms and make DAMN SURE it's
charging them properly.

Thanks,
-- 
Phil.                              | Acorn RiscPC600 SA220 64MB+6GB 100baseT
philpem@philpem.me.uk              | Athlon64 3200+ A8VDeluxe R2 512MB+100GB
http://www.philpem.me.uk/          | Panasonic CF-25 Mk.2 Toughbook
... Anything not nailed down is a cat's toy
-- 
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