[arm-allstar] DIY CM119 pin 48 voltage

[James WD0JB]

On pin 39 I get the same reading of about 200mv. The radio adapter is the
uv82 wiring from hamvoip, however with a npn bjt instead of the mosfet.

Thanks for all the help. I've got some more sound fobs on order.

James WD0JB

On Sun, Apr 28, 2019 at 18:59 Kevin Custer <kevin at kc-wireless.com> wrote:

> 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> 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
>
>
> --
73,

James WD0JB