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koda2

Well Known Member
I am working on putting several LED annunciators on my panel which will indicate a "hot" condition, i.e. lights, fuel pump, etc. I am also going to keep it as simple as possible, no test circuits, equalizers, dimmers, etc.

It would seem the LED lead would come off the on side of the switch and go to the LED via a very small and short wire. What is the proper way to fuse this wire, or..not?? Fusible link would have to be tiny and hard to troubleshoot.

Dave A.
6A build
 
I understand the desire for simplicity, but.....

It appears to me that an annunciator without a test circuit may leade to a false sense of security. How can you validate that the circuit is functional?

VxAviation has some designs that allow you to build a rather simple annunication panel that can handle both high and/or low situations.
 
If all you want to do is annunciate the switch position, then yes, a series resistor and LED off the switched terminal of the switch is all you need.
 
How does the resistor work as compared to the fusible link? I understand the fusible link, does the resister blow in a short situation the same way as a fusible link?

Thx
 
I think Mike is referring to the resistor required to make an LED work.

Originally, my panel had a 6 light annunciator panel with all the bells and whistles. After flying a while I found it annoying and unnecessary. I've since replaced it with 3 indicator LED's (all red). Two of them are flashers. They are:

Low Oil Press.
Low Voltage.
Boost

If the engine is running all the lights are off. If the master is on and the engine is not running, low voltage and low oil pressure are flashing. If the boost pump is on, then the light is on. Circuit testing is built into the function. Dimming is unnecessary because the lights are off in flight.

I'm working on a timer circuit that will delay the boost pump indicator light coming on for a few minutes so it works as more of a reminder to turn it off.

my $0.02
 
Since your talking LEDs, I came recently came across these and have installed them in a few friend's airplanes. They come in green, red and yellow: No resistor required.

If you want to add a resistor, they have blue too.

Here's the LED home page which includes some nice LED strip lighting which I've played with using this dimmer (works GREAT and inexpensive!) :) Rosie
 
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MPJA

I have some of the MPJA indicators that were posted previously on several threads. Although they are not on here they seem to work perfectly on the "test bench" when wired up to a 12v circuit. No dimming required.

annun2.jpg


I am also familiar with the Push-to-Test indicators that the military uses, but going that far seems a little much for a day-VFR plane without sophisticated equipment and a non-critical mission.

Some of the indicators I have set up, such as the alt-out or low-oil-press, are duplicated anyway in the EIS 4000 system.

The problem as I see it, is, if the LED indicator wire is not protected with a fuse or a link, a short could take out the main fuse, rendering the needed utility inop, without a good reason.

Dave A.
6A build
 
If you wanted to build a push-to-test type function with standard LED indicators you can make a simple "Diode OR" circuit. Two diodes are used for each LED to logically OR the two inputs. One input is your standard status input and the other is your push to test. The diodes act to isolate the two sources so you don't cause a short when you press your push-to-test switch. These diodes are probably $0.05/each so it can be done very inexpensively.

You should know that this type of circuit tests the indicator is working it doesn't test the connection from your status input.
 
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