At 07:53 AM 8/20/97 -0400, you wrote:

>Anyone have any suggestions? Simple and cheap is better. A little
>sophistication in the software is much easier for me.

Easiest I know of is a diode (pointing down) between the gnd pin of a
regulator and the actual gnd. Put a transistor across this to short out
the diode(s) and you have simple digital control from 0.4 to 0.7v,
arrange a couple with a trim resistor ans that should do it.

I used a 3v3 zener in the gnd line to a 7812, but had to make sure the
zener had some regulated working current - so resistor from output of
regulator to gnd pin of regulator and zener (pointing up) below that
with anode of zener connected to ground - this was for a automotive
simulator voltage supply for a test jig - but principle is the same.

Rgds

Mike
Perth, Western Australia