Dimming a Gemini ADI

[Darin Watson]

I have a Gemini ADI (https://www.bendixking.com/content/...rak-Gemini-Series-ADI-Installation-Manual.pdf) and for dimming pin 2 is a voltage input. I spoke with King who still supports this for TT and they told me that a PMW dimmer would work with this input, and in fact that it was designed for this type of input.

I am using a channel from this dimmer (https://www.aircraftspruce.ca/catalog/elpages/4channeldimmer13-15799.php) and the Gemini dims, grows brighter to close to full bright, then dims again on about a 1.5-2 sec cycle.

I am not an electronics guy, but suspect that there is little to no current being drawn by the Gemini, and that the voltage keeps rising.

Would a high resistance bleed resistance so that 5mA is being drawn stabilize things? It there other advice?

 

[BobTurner]

Well, I know nothing about the box in question (Gemini). That said, I know of no other avionics that is designed to take a PWM input into a dimmer input. Usually they just want a simple dc voltage. Easy enough to test. Or call Bendix-King back, make sure they understood your question.

 

[Darin Watson]

Solution

Well a funny yet somewhat embarrassing story….hooked up a channel to the ADI dimming input which caused the display to dim and slowly get brighter, and then back to dim. Because I was using the other three channels for brow lights, map lights and convenience lights I really wanted to use this solution so all of the dimmers were identical.

Not knowing the exact design of, what is likely a high impedance input for the ADI, with very little current flow I thought that a small bleed current with a capacitor and resistor to limit current to 100mA supply a smooth voltage to the ADI input. DID NOT WORK…just pulsed at a slower rate

Then I occurs to me that there is a basic rheostat wiper that is an input to the PWM module, and with low draw for the ADI one could use that as a direct input. Tried it and it worked slick, and keeps all dimmer knobs with the same look and feel 3-4 hrs messing around with the bleed current idea when a much simpler and cleaner solution was 10min ….oh well live an learn. Thought I would post for others.