[App_rpt-users] USB FOB not affecting Pin 13 to PTT

Kevin Custer kuggie at kuggie.com
Thu Nov 24 17:11:11 EST 2016

You are missing something....   On most FOB's, regardless of the 
manufacturer, the RED LED is not wired to pin 13.  While the green LED 
usually works correctly because it's tied to pin 12 on the C-Media chip, 
the red LED by default is connected to pin 21.

There are several reliable sources for non potted FOB's, but generally 
they cost more.  The SYBA UAUD71 and the StarTech ICUSBAUDIO are two 
such units.  They generally cost between $11 and $17 depending on supplier.

I've recently dropped the price of the RA-35 to include the CM119A and 
EEPROM to be presoldered.


On 11/24/2016 3:20 PM, no1pc at yahoo.com wrote:
> I have a few USB fobs resembling the one shown in the document titled 
> "USB FOB to DB25 Interface"
> Unfortunately the chip itself is potted die-on-board so access to 
> signalling lines is limited to the additional components on board, 
> which should seem simple enough to get to Pin 13 that feeds the Red 
> LED to extract a PTT signal.
> (I am able to assert COS- to Volume down and get received audio "to 
> the net" experienced with WebTransceiver.)
> Unfortunately metering 'every' available connection and toggling 
> WebTransceiver's Key/Transmit, none of the signal lines on the board 
> react.  I could imagine one line or the other might be open-collector 
> and I'd have to add a pull-up to see a transition, but with the LED 
> still in-circuit I'd think that would react.  (The Green LED works as 
> heartbeat just fine.)
> Before I head to the local Frys and buy 1-2 each every fob they have 
> to gut to see if I could get to the chip pins directly (or try to be 
> patient and wait for Amazon)...
> ... I'm sitting here looking at a fully functional micro with a LOT of 
> GPIO pins available...  wondering why, aside from the IRLP s/w and 
> interface options available... doesn't an AllStar implementation 
> leverage the on-board signalling?
> I see there is Python code around to work with the GPIO, but not quite 
> yet sure how or if I could create and call PTT and COR (and CTCSS) 
> sense scripts within the AllStar configuration - ???
> I know it would split out the radio audio v PTT/COS wiring harness 
> just a bit vs the cute USB thing, but what the heck - buffer/interface 
> parts on a small perf board tied to the GPIO pins and done?  No?
> Am I missing something?  Code- and instructions-to-be?
> Using Pi 3 Model B v 1.2
> BTW, uname -a yields: "Linux barf3 3.18.0-trunk-rpi2 #1 SMP PREEMPT 
> Debian 3.18.5-1~exp1.co1 (2015-02-02) armv7l GNU/Linux"
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