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Doll's Eye Indicator

paul330

Well Known Member
I have a dual Dynon system with a TruTrak wing leveler as one of the back-up instruments. I am looking for a way to indicate that the power has failed to the TruTrak as it has nothing internal.

I could sense it and display on The Skyview but that makes no sense as I probably only need it if the Skyviews have failed! Likewise, I can't use a relay and a light as it is not failsafe and, again, I am only likely to be on standby if there has been some sort of major instrument or electrical failure.

I am thinking about some sort of magnetic dolls eye (a la 1960s) that is held in the ON position by power and goes OFF or barbers pole when power is removed. Anyone know where I can get something like this or have any other ideas? Maybe I am missing something very simple.......
 
Why can't you use the normally closed contacts of a relay to turn on a light? It seems fail safe to me as long as there is a reliable source of power for the light. When power fails to the TruTrak, the relay drops out.
 
There is the problem - if the power fails, where do I get the power for the light from? I can't use a hot battery buss as it will run down the battery - for the same reason, I can't use a separate battery pack.

I was thinking about building some sort of capacitor driven pack which would recharge and provide a reasonable ON time for an LED. Any electronics gurus?
 
There is the problem - if the power fails, where do I get the power for the light from? I can't use a hot battery buss as it will run down the battery - for the same reason, I can't use a separate battery pack.

I was thinking about building some sort of capacitor driven pack which would recharge and provide a reasonable ON time for an LED. Any electronics gurus?

If you use an LED I would think you would be on the ground LONG before the LED ran the battery down....
 
Yes, but if I am on a hot battery buss then the light stays on forever and runs down the battery on the ground.

Since I would only be on this instrument if I had a major power/instrument failure then I can't rely on there being power on any of the switched busses.

I suppose I could take wires from a couple of sources and use a diode.
 
Guess I'm not understanding your system. Where is the power to the TT coming from? Could you tie the anode of the LED to the switched side of your master solenoid? Then when you turned off the master the LED would go out?

Or could you connect the LED across the TT power connections? It would be on as long as there was power, and go out when power was lost?
 
OK, I think I have it.

The TruTrak is powered from the E-Buss. So I splice from the Trutrak power wire to control the relay but splice to the Main Buss for the light power. This will catch either an E-Buss fail or wire break. Loss of main buss loses the light but won't matter since E-Buss (and therefore the TruTrak) will still be powered. If I lose both busses, I think I'll know about it! - and in any case will still have the Skyview on backup battery.

The only thing it won't cover is loss of Main Buss plus a wire break but I think that comes into the 10 to the -9 category.......

I'm not really that fussed about having a light at all but it is a legal requirement for IFR to have a power fail indication. I mean, how likely is it that I am going to lose both screens and have an E-buss fail?

Still think a 60s style Doll's Eye would be cool, though............
 
This seems like quite a lot of effort to detect a failure of the power supply to the instrument. What about a failure of the instrument itself? To me an issue with its internal sensors or moving parts seems more likely than a wire spontaneously breaking.
 
I agree but thems the rules in South Africa - you must have indication of loss of power to an instrument
 
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