FM1200 4m gateway

[2E0SAU]

I am using an FM1200 as a 4m internet gateway and have just built a new interface to link the radio to the computer. This interface has a PIC chip to control all the switching instead of relying on just VOX audio and also has a built in DTMF decoder.
This has presented me with a problem as I need to obtain a +5v ( COR signal ) from the radio when the squelch opens in order to trigger the interface switching. The interface will also work with reverse switching, in other words the +5v can be present when idle and drop to zero when the squelch opens. I have tried using the gate that operates the green LED on the display unit but this only seems to switch the ground side of the LED
Anyone know where else I can look in order to pick up a squelch switched 5v ?
Cyril 2E0SAU

[G8JGO]

Hi Cyril,

Have you considered a simple 5V pull up resistor on the ground side of the switched green LED as input to the PIC?

If you look at the PIC docs, you can set internal pull ups, but I've always favoured external ones.

As you state, using software control for the COR then logic sense (true/false) does not not matter.

Hope this helps.

[G3PTU]

Saturated transistor switching stage
Base from 'Earthy' end of L.E.D. via 10KR??
Emitter - earth - 0Volt
Collector , pull up with (say) 1KR to 5volts.
Device - BC107 or What have you?
[ Capacitor from Base to Emiter to remove wiskers etc - 1Kpfd?]
logic Statement is:- Collector = NOT Base

David G3PTU