[arm-allstar] DIY CM119 pin 48 voltage

[Doug Crompton]

Jim,

 Right at the pin you should see a weak pullup of about 2-3 volts BUT if
the diode as described is connected in series off of the FOB COS pin you
will see little or no voltage on the side away from the FOB as it is
blocked by the diode. Grounding the diode on the side away from the FOB
should pull the pin 48 voltage down to close to .5 volts or less.

The purpose of the diode is to not allow positive DC voltages from outside
the FOB to reach it. So a rig could have a positive +12 volts high and a 0
volt low for COS and it would not damage the FOB. Most radios operate in
the 0 to +5V range. So in all cases you are only pulling the COS pin low to
trigger but the low could indicate a true signal or not depending on the
setting of item J in simpleusb-tune-menu to usb or usbinvert.


*73 Doug*

*WA3DSP*

*http://www.crompton.com/hamradio <http://www.crompton.com/hamradio>*

On Sun, Apr 28, 2019 at 9:29 AM "James WD0JB via ARM-allstar" <
arm-allstar at hamvoip.org> wrote:

> Quick question, I hope. What voltage should I expect to see on pin48 COS on
> the CM119 chip? I expected there to be at least 3-5volts but when I place a
> multimeter in 2.5volt range the needle barely even moves.
> The problem I am troubleshooting is ptt and transmitted audio are working
> but I can't seem to get recieved audio to register. And I think it is due
> to the COS signal not properly being sent.
>
> I hope this makes sense. I've never had to troubleshoot much digital logic
> before. But seems simple enough, I think.
>
> I appreciate any help that can be provided here.
>
> James WD0JB
> --
> 73,
>
> James WD0JB
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