-=> Robert Mcginity said to Greg Mayman
 -=> about "LOOKING FOR A SCHEMAT" on 11-16-04  20:23.....

 RM> Actually, what I am looking for is a schematic that will remain off
 RM> until the input voltage is ABOVE 13 volts.  Once that is achieved, I
 RM> can easily design and build the remainder of the system.  A car's
 RM> regular battery will remain at less than 12.7 volts until the
 RM> alternator is turned on which then charges the battery at about 13.8+
 RM> volts. 

A simple comparator circuit will do it. The ref input can be fed
from a zener diode and the other input from a potentiometer
between the +12v and ground.

IIRC there is a chip that contains a comparator and a reference
source.... one of the LM- series, I think.

   ,-./\
  /     \ From Greg Mayman, in beautiful Adelaide, South Australia
  \_,-*_/    "Queen City of The South"    34:55 S  138:36 E
       v

... Anticipate trouble but don't go looking for it.
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