single op-amp window comparator

[Lee]

the usual circuit design of a window comparator uses two
op-amps...does anyone know about a single op-amp window comparator
circuit...tnx in advance
a simple hack version comes to mind.

using an OP-AMp from a +&- rail supply to get a
0 volt output into a mini bridge rectifier to convert
the signal to always + or - what ever.

by setting setting one input of the Op-amp to a voltage
and using the other to monitor the external source voltage,
one can then adjust the gain using a loop back into the -
input and adjust the + input for the comparator center point.
the idea is to produce no voltage or low voltage at the
output as the reference voltage starts to get near the set
voltage..
basicly we are looking at a simple OP-amp circuit that you
can set the + input using a dual rail supply.

the output can drive some schmitt
trigger or mechanical relay etc..

like i said, just a hack in thinking of course.

do you have any example...i really need a circuit for this...tnx