Hi David (David VanHorn), in <009001bd73d9$ec1d90e0$85f135ce@xenu.iquest.net> on
 Apr 29 you wrote:

> Check the output pin spec, you'll find that the maximum low voltage is high
> enough to keep the base of an NPN active. Add an additional resistor from
> the base to ground, probably 2.2k or 4.7k, and the problem will dissapear.

Better yet is a diode (1N4148 or other) in series with the pin, that raises
the switching voltage by about 0.7V - enough for usual uC output pin specs.
It consumes no extra power, works with pullup outputs, and makes no
assumptions about the port pin (theoretically a low output could _source_
lots of current at 0.4V for example and still stay in-spec).