BC780XLT carrier operated lighting instructions here

I figured I would make a new thread that's easier to find if someone searches.

I originally intended on using FETs due to the their sensitivity and high resistance but ended up finding a location that works with regular NPN cheap small signal transistors and a cheap 1N4148 diode.

I encountered on radio that did not like the mod and required two diodes in series to further drop the voltage to base.

The transistor base is switched by the SCAN CONTROL line at IC11 pin 7 but I found a plated through hole at the bottom where the connection can be tapped, keeping all parts on the bottom where it's easy to work. The other location is one of the backlighting control transistor connection plated through hole locations.

The image is the top of the radio (board sits upside down) with the front toward the viewer.

This mod makes the back light come on regardless of the menu. I have the bank of 16 radios I have sitting together and it's very difficult to see which is active. With this mod I set all radios to backlighting off and they glow when a carrier is present. So far it works very well.

It would be a good idea to put a drop of glue on both parts if the radios are used mobile. The connections are very small and not that physically strong. I didn't bother to do this because all my radios just sit in a desk overhead shelf. Thanks to pro92b and the others in the other thread for their assistance.

"Oh Christmas tree, oh Christmas tree..."
Looked neat but i would be worried about the little 'grain of rice' lights burning out from being turned on and off rapidly.

Nice work on the circuit. I can see how you'd want that with 16 780s.

Two observations:

1. It looks a little frantic at times!

2. This is regardless of your backlight mod: when you have 5 or 8 becoming active at once...how do you know what you're hearing from which one? I get brief open carrier hits when I scan mil air on my 780; I am imagining you get that too, along with real hits. Or do you not care because you're logging everything separately for listening later?

n4yek said:

"Oh Christmas tree, oh Christmas tree..."
Looked neat but i would be worried about the little 'grain of rice' lights burning out from being turned on and off rapidly.

Click to expand...

They are LED.

eorange said:

Nice work on the circuit. I can see how you'd want that with 16 780s.

Two observations:

1. It looks a little frantic at times!

2. This is regardless of your backlight mod: when you have 5 or 8 becoming active at once...how do you know what you're hearing from which one? I get brief open carrier hits when I scan mil air on my 780; I am imagining you get that too, along with real hits. Or do you not care because you're logging everything separately for listening later?

Click to expand...

The demonstration video was noise generated locally to get them to activate. I have rarely had more than three active at once in normal operation.

Nice mod & setup!