I don?t know how many times I have looked at a problem and come up with a solution on my own ? then later on, saw a much simpler, more elegant, or simply better solution to the same problem executed by someone else. It does give truth to the idea of getting outside help and opinions on whatever we are doing ? either it will help us to do better, or confirm our own brilliance in design. Either way, the project wins if we do it better! I am sure that folks will have their own inputs and stories on this?.here?s mine:
I like to have annunciator lights for various functions in the cockpit ? some are warnings, and some ?reminders? (?Hey Dummy? lights we call them) that remind us to do things like turn off fuel pumps or not leave the landing lights on. Sure, the switch position will tell you these things, but a light will more quickly get your attention. And if you have never forgotten anything (or missed a checklist item) in a cockpit, you are a far better pilot than all the aviators I have ever known. So when I build a panel, I have an assortment of lights that I like to have, and each one has its own ?input? ? some from a switch, some a voltage sensed on a circuit, etc. These discrete inputs come in two flavor s? a voltage or a ground.
Building annunciator lights is super simple these days with the advent of 12volt LED indicators. They are simple, easy to install, and look good. They can also be dimmed by dropping the voltage through them with a resistor or potentiometer. I find that I generally want them really bright, or really dim, and while my RV-8 has a potentiometer to give me a wide variation, I find that I either use it full up or full down. Therefore, for the RV-3, I am just putting in a switch to select ?bright? or ?dim? ? it is simply a line with or without a resistor. If you gang the ground side of the LED?s, you can dim them all at once ? really slick!
Unfortunately, this ganged approach only works with LED?s that have a common switching mode ? either power or ground. You can tell that a light circuit is powered by drawing a voltage off the switch to light the LED. But EFIS alarms generally give you a ?ground? when they are active ? this means switching the other side of the LED. It?s hard to gang them this way, so what I have done before is use a simple 12 volt relay as an inverter to switch the ?ground? to a ?hot?, or vice versa. This works, but now you have introduced moving parts and complication to the system.
So the other day, I had another builder/engineer looking at the project. I explained how I built the annunciator, and that I was getting ready to wire up relays for the ?backwards? stuff. He looked at me funny and said ?if you?re going to use only two brightness positions, why not just use a DPDT switch, and run the ground switched circuits through one pole, and the hot switched circuits through the other? It?s all solid state!?
Well Duh!! Sure, of course ? that?s the answer! I can?t believe it took me so long to see such an elegant solution?.(here?s the drawing by the way).
See what I mean? Sometimes, you just need another set of eyes, or someone looking from another direction to help you out. We no longer build our airplanes in a vacuum ? let others see what you are doing, and be open to suggestions ? it just might save you time and trouble?.
Paul
I like to have annunciator lights for various functions in the cockpit ? some are warnings, and some ?reminders? (?Hey Dummy? lights we call them) that remind us to do things like turn off fuel pumps or not leave the landing lights on. Sure, the switch position will tell you these things, but a light will more quickly get your attention. And if you have never forgotten anything (or missed a checklist item) in a cockpit, you are a far better pilot than all the aviators I have ever known. So when I build a panel, I have an assortment of lights that I like to have, and each one has its own ?input? ? some from a switch, some a voltage sensed on a circuit, etc. These discrete inputs come in two flavor s? a voltage or a ground.
Building annunciator lights is super simple these days with the advent of 12volt LED indicators. They are simple, easy to install, and look good. They can also be dimmed by dropping the voltage through them with a resistor or potentiometer. I find that I generally want them really bright, or really dim, and while my RV-8 has a potentiometer to give me a wide variation, I find that I either use it full up or full down. Therefore, for the RV-3, I am just putting in a switch to select ?bright? or ?dim? ? it is simply a line with or without a resistor. If you gang the ground side of the LED?s, you can dim them all at once ? really slick!
Unfortunately, this ganged approach only works with LED?s that have a common switching mode ? either power or ground. You can tell that a light circuit is powered by drawing a voltage off the switch to light the LED. But EFIS alarms generally give you a ?ground? when they are active ? this means switching the other side of the LED. It?s hard to gang them this way, so what I have done before is use a simple 12 volt relay as an inverter to switch the ?ground? to a ?hot?, or vice versa. This works, but now you have introduced moving parts and complication to the system.
So the other day, I had another builder/engineer looking at the project. I explained how I built the annunciator, and that I was getting ready to wire up relays for the ?backwards? stuff. He looked at me funny and said ?if you?re going to use only two brightness positions, why not just use a DPDT switch, and run the ground switched circuits through one pole, and the hot switched circuits through the other? It?s all solid state!?
Well Duh!! Sure, of course ? that?s the answer! I can?t believe it took me so long to see such an elegant solution?.(here?s the drawing by the way).
See what I mean? Sometimes, you just need another set of eyes, or someone looking from another direction to help you out. We no longer build our airplanes in a vacuum ? let others see what you are doing, and be open to suggestions ? it just might save you time and trouble?.
Paul
