Sean A. Walberg writes:

> I'm trying to build a simple charger for my drill batteries (9.6v NiCad).  
> Taking apart the charger, it just connects the 12v/400mA wall wart across 
> the battery terminals.  This appears to work, but I have to watch the 
> batteries carefully and remove them once they are charged.
> 
> I thought it would be a simple matter to have a PIC control the input and
> only apply charge when the battery voltage is underneath a certain
> threshold.  However, reading the datasheets, the Vref on the A/D is
> limited to Vdd plus a bit, and I need to be able to measure up to ~10V.
> 
> A resistor divider network could bring it down to something reasonable, 
> but I was hoping for other options.

Take a look at this PIC-based NiCd/NiMH charger:

http://www.angelfire.com/electronic/hayles/charge1.html

It's a deceptively simple circuit, yet it provides close to optimal
charging characteristics.  There is a very good circuit description as
well.

-p.
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