[arm-allstar] DIY CM119 pin 48 voltage

[Kevin Custer]

James,

With nothing connected to this pin (48 for COS) it should ride at 3.3V 
or so.  If that's not what you are getting, the CM119 is likely bad.

What do you read on pin 39?  What kind of radio adapter do you have?

Kevin


On 4/28/2019 11:47 AM, James WD0JB wrote:
>  Doug and Kevin,
>
>  I think I understand what you're trying to say all of this. What I am 
> testing is the voltage on pin 48 with nothing attached and I am seeing 
> about 200 mV. I don't believe that this is correct. Correct me if I'm 
> wrong please.
>
>  In that case, I believe that I have a faulty chip or I possibly 
> damaged it myself.
>
> Also,  in ASL 1.01, where can I find the real-time status of the PTT 
> and COS functions?
>
>
> James WD0JB
>
> On Sun, Apr 28, 2019 at 08:53 Kevin Custer <kevin at kc-wireless.com 
> <mailto:kevin at kc-wireless.com>> wrote:
>
>     James,
>
>     There is much confusion surrounding the COS and CTCSS inputs to the
>     CM1XX chipsets.  Here is a dissertation I wrote some time ago, that
>     hopefully explains the situation well:
>
>     The COS and PL "hardware" logic inputs on CM1XX based radio adapters
>     were originally the volume-up and volume-down functions, actuated by
>     manual (push button tactile) switches in a standard audio adapter
>     (FOB).  These inputs are internally pulled high, to 3.3 V, and
>     have to
>     be pulled low enough to become valid.  As such the push-button
>     switches
>     made a good ground when depressed, as that's what the other side
>     of the
>     switch was tied to - ground. Most AllStar radio adapters use
>     protection
>     diodes (BAT-43's) that don't allow voltage to be sent into the CM1XX
>     chip.  If voltage is allowed to be inputted to these pins, the
>     chip is
>     destroyed. So - with the diodes in place, it doesn't matter what
>     voltage
>     is present on the COS or CTCSS hardware inputs, because voltage on
>     these
>     pins doesn't make anything happen, and because of the protection
>     diodes,
>     doesn't hurt anything if voltage is present. Pull-up resistors are
>     totally unnecessary, because we need a ground to assert the condition.
>
>     Okay, so the CM108/119's logic inputs are looking for a ground to be
>     valid.  This "active low" condition is required NO MATTER if the
>     setting
>     in the conf file is upright or inverted.  So - the setting in the
>     configuration file doesn't change the fact that the adapter needs an
>     active low to be valid and assert the condition. All this software
>     setting does is change if the low condition exists when the radio is
>     hearing a valid signal, or when it's not.  Using a DMM, you can
>     read the
>     voltage on the CM119 side of the BAT-43 diodes to see if the logic
>     level
>     is properly changing from 3.3 to 0.0 (or a few tenths of a volt).
>
>     Not all radio logic signals are created equal.  Some logic
>     circuits can
>     source current, but lack the ability to sink. Sometimes active high
>     circuits (circuits that provide a voltage when the state becomes
>     active)
>     don't have the ability to pull to ground very well. These circuits
>     may
>     not have the capability to pull the COS and CTCSS inputs low
>     enough on
>     the radio adapter to become valid/active.  A pull-down resistor can
>     help, but nothing beats a real active low circuit.  A 2N2222 (or
>     similar
>     NPN transistor) with the emitter grounded usually works well.
>
>     Hope this helps...
>
>     Kevin
>
>
>
>
>
>     On 4/28/2019 9:26 AM, "James WD0JB via ARM-allstar" 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