Push to test circuit for LEDs

[pmnewlon]

I haven't been able to get to the matronics.com site today, seems like they must be having trouble.

I am looking for a basic 'push to test' wiring circuit for seven LEDs on my panel. Anyone have such an animal around?

Thanks,

Phil

[GOEZ]

It depends on how your LEDs are already wired. The following two circuits should give you a starting point. The diode type really isn't critical and you can expand the circuit as required ... I just happened to have this diagram around that shows three different kinds of displays. Adding four more diodes will expand it for seven indicators.

For indicators where the sensors switch the ground for the indicators:



For sensors that switch the positive side of the indicators:



If you have a mixed setup then you can add some extra electronics or the easiest solution is to just use a double pole TEST switch.

[pmnewlon]

Thanks Bill!

What accommodation has to be made for a circuit that has the LED lit with the engine off and others that are (possibly) lit when the engine is running? Is that what the diodes are for? As an example: the low oil pressure, low voltage and low fuel are lit with the master on but the engine off. The low oil pressure and low voltage go off when the engine is started but the low fuel condition doesn't go away. Would the circuits you showed be appropriate for such a condition?

Phil

[Birkelbach]

Whether the engine is running or not is irrelevant. It won't affect either of these circuits. The only difference between these two circuits is whether the switch is on the high side or the low side of the lamp/led. The diodes are there to isolate the circuits from one another. If you remove the diodes then all the switches would be directly connected to all the lamps. If one switch trips, all the lights would come on. The diodes eliminate this problem by acting like a check valve.

[pmnewlon]

Originally Posted by Birkelbach

If you remove the diodes then all the switches would be directly connected to all the lamps. If one switch trips, all the lights would come on. The diodes eliminate this problem by acting like a check valve.

Ah, that makes sense. Thanks! Phil