[App_rpt] Radio Interface Question

[Steve Rodgers]

James, 

See below--


On Tuesday 07 March 2006 15:28, James Harfield wrote:

> Measuring the levels of the speaker audio, regardless of volume level
> on the radio, the voltage does not break 1.5v.  Looking at the
> documentation for the card I felt that this was appropriate.

The potential problem here is that someone can mess with the receiver volume 
control and mess up the audio levels. 

>
> I'm using regular Ground as of now.  Grounding PTT with "Ground" and
> not "RF Ground" keys the radio as it should.  So I'll just move my
> ground pin to there and leave PTT where it is.

Sound like a good plan.

>
> What I'm doing now is making a small circuit to work as COR.  I can't
> seem to find a working version of the COR in the radio pin out, so I've
> taken a MOSFET and 5v battery to switch the level from 5v to ground when
> a signal is present and stay at 5v when no signal is present.  Unless
> I'm blindly missing something to pull off the radio that will work the
> same way.  Something like:
>
>                       +5v
>
>                          10k
>                        _ |--------------to PCI card
>
> >from radio-- |_
>
>                         gnd

May I suggest you get the schematic to the radio, and look for the transistor 
or electronic switch which is used to mute the audio? If you can find some 
point in the squelch circuit which swings from 5 volts or higher to ground, 
use this as your COR. The COR input as a 1 megohm input impedance. You should 
be able to find a point in the radio which will provide the signal for you.

>
> ASCII art may be butchered in the post though.  The level from the
> radio should be enough to activate the FET and pull that output to
> ground, while allowing the 5v to pass to the card when there is no
> signal.
>
> Just for reference so you know where I'm coming from, I found a couple
> of Motorola HT600s on eBay with charger for pretty cheap and am playing
> with those since they seemed to have easy access to signals with the 13
> pins on top.  I thought this would be good to learn with while not
> investing tons of money in expensive radios to break.  Thanks for the
> help while I struggle through this process.

HT 600's should interface nicely. Take a look in the service manual to 
understand what I'm talking about. The way the speaker circuit works, also 
doubles nicely for COR. The audio output stage is powered down when there is 
no signal. 





>
> -JRH
> _______________________________________________
> App_rpt mailing list
> App_rpt at lists.illiana.net
> http://lists.illiana.net/mailman/listinfo/app_rpt