[arm-allstar] Question on simpleusb-config.sh script

[David McGough]

Hi Lawrence,

That text is a little confusing sounding, but is accurate in this 
context, where a 2n4401 transistor is being used for keying.

The transistor, setup in an open-collector, common-emitter configuration,
acts as an logic inverter.

>From the CM1xy chip and software standpoint, for "normal" operation
(invertptt=0), PTT active is a logic-hi value (near +3.3V). So, with
invertptt=1, PTT active becomes logic-lo (near 0V).

Then, add the transistor to this setup, and those logic value are 
reversed.

So, when invertptt=0, and AllStar PTT is active, the transistor is turned 
on, pulling the actual PTT signal low.

And, alternately, when invertptt=1, the transistor is off, allowing the 
actual PTT line to float high.


Does this make sense?

73, David KB4FXC


On Thu, 26 Oct 2017, "Lawrence Roney via arm-allstar" wrote:

> Thanks Tim, however that is not what is displayed on screen when executing the script. It says,

invertptt=1                                                            
              ; Invert PTT 0 = ground to transmit, 1 = open to transmit  
              ; This is the collector lead of the 2n4401 on the modified
              ; usb sound fob

I still think something is backwards either in the script's logic, the 
comment lines, or the way the y/n question is worded.  When you answer 
(YES) to the question "Should PTT be grounded to transmit?", it writes 
invertptt=1 (open to transmit)

Lawrence

=========
Date: Wed, 25 Oct 2017 17:25:57 -0700
Tim Sawyer wrote: 

apt_rpt assumes high true as is typical in boolean logic. Therefore low true is inverted.

On Wed, Oct 25, 2017 at 4:34 PM, "Lawrence Roney via arm-allstar" <
arm-allstar at hamvoip.org> wrote:

> Not sure if this is an error or not, but it seems backwards and the
> question came up when configuring some nodes for our club members.
>
> When the simpleusb-config.sh script comes to the PTT Setting section, it
> asks "Should PTT be grounded to transmit?".  Currently, answering YES
> (grounded to transmit) writes 'invertppt=1' to simpleusb.conf.  This does
> not seem correct.  Shouldn't answering YES write 'invertptt=0'?
>
> Maybe the question should be, "Should PTT be INVERTED to transmit?"  Just
> wondering...
>
> Thanks,
>
> Lawrence - N6YFN
> Henderson Amateur Radio Club
> www.w7hen.com




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