Green 2.5mm tip rx audio + Blue 2.5mm sleeve rx audio gnd, ptt GND, rig gnd Bare 3.5mm sleeve tx audio gnd, ptt +V, NB NOT rig ground Red 3.5mm ring tx audio +
To key the PTT, current must be able to flow from Bare (3.5mm sleeve) to Blue (2.5mm sleeve).
That is, either short Bare and Blue (sleeve to sleeve), or a current should be able to flow from Bare (3.5mm sleeve) to NPN transistor collector, to emittor, to Blue (2.5mm sleeve). An NPN transistor conducts from collector to emitter when a voltage is applied between base (+v) and collector (gnd)) – 5V + 1k resistor.
In other words:
The radio puts 3.3V down the Bare (3.5mm sleeve) conductor.
To key up, this must be shorted to the Blue (2.5mm sleeve) conductor.
RX audio is present between Green (2.5mm tip) and Blue (2.5mm sleeve)
TX audio should be pushed in to Red (3.5mm ring) and Bare (3.5mm sleeve)