There are a number of monitoring applications in Safety Instrumentation
where you want to check for a fault on a circuit. Also a lot of cars
monitor lights and doors now.

To clarify the design criteria..
The circuit can be designed to indicate if a remote light is active.
But.. The circuit can also be designed to check for open circuit when a
remote light is inactive.

Take a fire alarm for example

_____________________________________________ ______________________
MonitorCCT
| | |
Supply
| Fire detector ( NO) | | End of Line Resistor
________________________________________________|_ ________________________|


The circuit is designed to monitor for open circuit ( No current through
monitor cct )
Fire -Maximum current through Monitor CCT.

There are also more sophisticated circuits that monitor each detector

Typical fire monitor cards in industry would be £300 each ..


To check a series bulb arrangement, a small current from a low voltage
source can be passed through the bulb when inactive and monitored to check
if there is continuity through the filament. So similar principle to the
fire detector. If no current at all there is a break in the circuit (
filament or wiring problem) small current, circuit ok but bulb not lit.
Apply a higher voltage, and you have a high current circuit and bulb is lit
ok .

The monitor circuit could be based on a couple of the GM050 circuits with
different supply voltages or something more sophisticated with a PIC to
complete the logic and operate the fault relays.

Is this a gap in the market???
Major opportunity here to make a million!.. out of yotties?? I won't order
the new car yet!

Regards

Bob
Simply Blue Too
Clyde

"CS" wrote in message
...
I am trying to devise a simple circuit to monitor when a 24v nav lamp
has blown. Found this
http://www.gammatron.com.au/datashee...0Datasheet.pdf
but at AU$54 it is pretty pricey. Should not be to difficult to make
up, but I need to know he values of the components. I already have
the switch, LED and a resistor to monitor when lamp is on.
TVMIA.