James said:
What I want to achieve is hard to describe but I'll try. Say I've got a v
simple circuit that includes a power supply and a bulb. I break the circuit
and want to put something in its place - this component would measure the
voltage and, providing it was in-between set boundaries (i.e. between 0.4V
and 1.2V or between 2.4V and 2.8V) would complete the circuit. If the
voltage was not within ranges specified, the circuit would remain broken. I
hope this is clearer
)
James
______
V+ ----A B-----+
|
[Bulb]
|
Gnd --------------+
What you described means the circuit must sense
the voltage between points A and B. You *don't*
want to do that - your description is not correct.
Every time you close the contacts that connect A to B
the voltage between them drops to 0 and your sense
circuit can no longer determine whether the contact
should remain closed or should open.
What you *do* want to do is sense the voltage between
V+ and ground. When that voltage is within a specified
range, you want points A and B connected.
You can use a window comparator to meet the above
requirement. I think you want more detail than just
the words "window comparator", but more detail on the
requirements is needed to do that. What is the load
current? What is the maximum range of V+ ? What
are you trying to do? Someone replied suggesting
you might want to discharge a NiCd - if that is the
case, say so.
Ed