[AX-O]

All,
I am hooking up my stick switches. I am trying to figure out how to use the left china hat movement to change radios. The china hat uses the center pin to ground the up/down/left/right movements. I have the up and down movement set up for the elevator trim.

The GMA 240 manual says that pin 20 (com swap in) and pin 21 (com swap in return) on the J2402 need to be conected to each other via a single pole MOM switch.

I want to use the left china hat movement to change the radios. How can I do that? Connect pin 21 to ground and pin 20 to the left china hat switch?

Or, do I just connect pin 20 to the china hat?

Thanks for any help or guidance you can provide.

 

[BobTurner]

Without a 240 manual in front of me, I'd say do not ground any 240 pins unless Garmin says it's okay. It may well be the return is internally grounded, but call them and find out.

If not then you need to go to Radio Shack and get their cheapest 12 volt relay. (Inexpensive is okay since you can always use the 240 to swap radios).
Wire the relay coil to 12 volts on one side, and to the coolie hat on the other side of the coil. Wire the relay contacts so the 2 pins from the 240 go to the normally open, and the "arm", contacts. Leave the normally closed not hooked up.

My advice? Skip it. I virtually never swap radios, not VFR nor IFR. I do listen to the #2 for ATIS while still on #1 with ATC, but that's different from swapping radios on the audio panel. In fact, I have the #2 on a wing tip antenna (which works not as well but okay), and I have to remind myself to call ground on #2 once every 6 months or so, just to see if it works!

 

[AX-O]

Bob, Thank you for the input.

Break

Forgot to mention this in the original post. I am not looking for advice on if I should or should not do it. Everyone's mission and personal background are different. What may work for me, may not work for the next guy. I just want to know if someone has done it and how they accomplished it. Thank you.

 

[az_gila]

Bob, Thank you for the input.

Break

Forgot to mention this in the original post. I am not looking for advice on if I should or should not do it. Everyone's mission and personal background are different. What may work for me, may not work for the next guy. I just want to know if someone has done it and how they accomplished it. Thank you.

I agree, do what you think is best for how you fly....

In my case, I'm going to use that switch to do a "FREQ. SWAP" on the active comm radio from the standy-by freq. to the in-use freq.

 

[g3xpert]

GMA240 COM Swap

All,
I am hooking up my stick switches. I am trying to figure out how to use the left china hat movement to change radios. The china hat uses the center pin to ground the up/down/left/right movements. I have the up and down movement set up for the elevator trim.

The GMA 240 manual says that pin 20 (com swap in) and pin 21 (com swap in return) on the J2402 need to be conected to each other via a single pole MOM switch.

I want to use the left china hat movement to change the radios. How can I do that? Connect pin 21 to ground and pin 20 to the left china hat switch?

Or, do I just connect pin 20 to the china hat?

Thanks for any help or guidance you can provide.

Hello Axel,

If you had a momentary contact SPST switch with two contacts you would connect that switch across pins 20 and 21 as shown on drawing B-1 to activate the COM radio swap when the button is pushed.

Due to the way your china hat switch is designed (to connect each active position to the center ground), you should be able to just connect pin 20 to this left china hat movement switch (and leave pin 21 disconnected) as long as the ground on that switch is common to the GMA240.

Let us know if you have more questions.

Thanks,
Steve

 

[AX-O]

Due to the way your china hat switch is designed (to connect each active position to the center ground), you should be able to just connect pin 20 to this left china hat movement switch (and leave pin 21 disconnected) as long as the ground on that switch is common to the GMA240.

Let us know if you have more questions.

Thanks,
Steve

Sir, just to make sure I understand the meaning of "common" with respect to ground.

I have J2402 pins 5,10 and 11 hooked up to a ground buss. I also have the ground wire on the china hat connected to the same ground buss. Is that what you mean by "common"?

or do you mean the china hat ground wire needs to be connected to the GMA 240 in a different way, like maybe to the GMA 240 avionics rack?

Thank you for your help.

 

[g3xpert]

Sir, just to make sure I understand the meaning of "common" with respect to ground.

I have J2402 pins 5,10 and 11 hooked up to a ground buss. I also have the ground wire on the china hat connected to the same ground buss. Is that what you mean by "common"?

or do you mean the china hat ground wire needs to be connected to the GMA 240 in a different way, like maybe to the GMA 240 avionics rack?

Thank you for your help.

Alex,

You are welcome. The way you have it connected should work fine.

Pin 21 is also connected internally to power ground, so your connection should be electrically equivalent to grounding across pins 20 and 21.

Thanks,
Steve