lml@lancaironline.net Mailing List Archive

Gary,

Do you have the circuitry diagram for the inverting relay? Is this the same as a latching relay?

We looked at the door side of the latch mechanism and decided to try the following: Using a 5 button contact switch set. The third button of the set has been used for a "Door Pump On" light. The 4th brings power to the door microswitch and the 5th takes it back to the annunciator panel, thru the LED and then to the common ground of the annunciator panel.

I also like Bob Pastuseks's approach on his LIVP. His is a little more complicated because you have to remove rool pin, remove the hex bolt, drill the head, and insert a roll pin to catch a microswitch. He has already done this so we'll use that if our idea does not work well.

Best,

John

Gary,
As you suggest, I found this to be both simple and pretty foolproof. The
"door unlocked" light will go out with the door open about 6 " at the
bottom--depends on how you adjust the electrical contacts--and I thought
that also served as a good reminder. When closing the door, check for the
light--it indicates that the circuit is active and functioning. If the light
goes out when you latch the door, all is well. If it doesn't, you have a
problem.

Bob Pastusek

The circuit for the "inverting relay" can be pretty simple. In my panel, built by Lancair, the warning LED's are wired for "low-side" switches - the wire has to be grounded to turn the indicator on. I haven't tested it, but generally LED's are over-driven when on and they will emit considerable light when the current is less than the maximum. The simplest way is to wire a resistor (fairly high power as the dissipation is significant) from the indicator to ground, turning the light on continuously. To turn it off, supply the resistor with power from the door switch. In that way an open circuit, caused by the door switch or by fully opening the door, will turn the light on. Another way is to use the normally-closed contacts of a relay. The relay coil is powered from the same breaker as the warning light circuit and is grounded through the door switch. Either of these methods produces continuous current drain while running, but not very much.

I also like Bob's approach the best - it follows the KISS principle and if the door is more than 6 inches open you know it anyway - no need for the light to be on continuously. And it gives you an opportunity to check that the switch actually switches at the appropriate time. I used the third contact on the standard door contact set, as I don't have a door pump operating light, sharing the ground wire with the pump. I'm reconsidering that - maybe I will put a small LED next to the switch. I didn't like the idea of potentially getting a warning in flight due to a non-flight-critical problem, but some make a good point in that there is no way to check that the pump isn't running continuously as there is always engine noise when you turn the pump on.

Gary Casey