Hi guys and girls

I am attempting to run two radios back to back and have run into an issue in order to PTT the radio I need a GPIO to go down to ground. So I need the one radio to key up when the other receives, so I have found a part of the circuit that gives a 3.3v when it receives so I proceeded to use an NPN transistor. The collector goes to ground emitter to the GPIO and base to the 3.3v on the other radio through a 1k resistor. Now this works and the radio keys up as I should. The problem I am facing is when the other radio stops receiving the 3.3v no longer disappears thus the transistor remains active.

More info
both radios run off the same supply
there is a 100k pull-down resistor on the receiving radio(3.3v to base)
there is a pull-up resistor on the GPIO so 3.3v is present

Any ideas what I am missing?

 

To start with, a schematic.

Also, what does "run two radios back to back" mean?

ak

 

when the one receives the other transmits and visa versa

 

On the RX im pulling the 3.3v from R118
On tx the PTT is pin 3

Does this help?

 

the RX is one radio and TX another

 

ok, an update I've tried to swap to an optocoupler and it does the same thing but as soon as I manually remove the ground from the led part of the opto then the 3.3v disappears as it should.

any ideas?

 

Ok I figured it out was a stupid mistake but wasn't on a component level the 2 radios where running the same frequency thus creating a loop