"Bill Degener" wrote in message
...
John Bachman wrote:
The subject tells the goal. Here is the rest of the story. There is
no micro available. It is preferred to use a dual comparator such as
393 as one of those is already part of the design and having two of
one device is preferable to one of these and one of those.

I have tried and failed. Others care to give it a crack?

John

My ESR meter works like that. check out this schematic and see if you can
use the circuit. http://www.mainelectronics.com/pdf/k7204inst.pdf


Not quite, it doesn't. The on / off button pulls the base of Q1 via D1 to
get Q1 going and put some power on the circuit. The switch also pulls port
line P26 on the micro, which responds by asserting port line P25 which
drives Q2 which pulls the base of Q1, completing the latched power-on
condition. So power is actually controlled ultimately by the micro.

Arfa