[Elecraft] ACC2 PTT 2.25/1.30 bug?

[Don Wilhelm]

David,

I did not have my brain fully in gear on this situation before.  The 
GPIO input is just that - an input to a 3 volt logic device with only a 
500 ohm series resistor.  So there is nothing to make it either a high 
nor a low level.  In the digital world it is known as a 'floating input' 
and without some other (external) hardware addition, it may appear to be 
either at a high or a low level depending on the "shifting of the winds 
in the desert"
Sooo - that may be a normal response when a LO function is used on the 
GPIO input signal.
Take note of the part in the menu instructions saying that some external 
interface circuitry may be required.

The GPIO input has no pullup resistor to 3 volts to keep it high - that 
means the voltage just floats at whatever it happens to be.  If that 
voltage happens to be below the logic threshold for a LO level, the 
function will become active when that menu option is selected - and will 
happen with nothing connected to the GPIO input. (The same might happen 
when HI is selected in the menu too).

The solution is to bring that input level to a high state with an 
external pullup resistor.  One end of the resistor goes to a voltage 
source (ideally 3 volts, but up to 5.5 volts will be tolerated.  The 
other end of the resistor goes to the GPIO input (ACC2 connector tip) - 
and oh yes, the negative of the source powering it would connect to the 
connector shell.  Two AA battery cells in series and a 33K resistor 
should work nicely and the batteries should last a long time.

Then your PTT switch, footpedal, etc. would place a short between the 
ACC2 connector tip and shell when it is active.

Note also that if you make the GPIO menu selections for either HI or LO, 
that condition may become active any time the plug is removed from the 
ACC2 jack.  In other words, you must connect an external high or low 
logic level before turning the KX3 on.

You may find it easier to build an adapter and use the microphone jack 
PTT input which has an internal pullup resistor which assures a high 
state when the PTT circuit is open or inactive.

73,
Don W3FPR

-----------------------------------------------------------
David,
Contact KX3support(at)elecraft.com to see if they can offer any 
additional wisdom.  If it has to go back to Elecraft for work, that 
contact at support is the starting place to obtain an RSA.

73,
Don W3FPR

On 10/18/2014 10:53 AM, David - KI4UVC wrote:
> Nothing is connected to ACC2 currently - I was mucking around with menu
> settings.
>
> I tried reverting back to MCU2.23 and am having the same issue - radio hangs
> at any change in ACC2 settings.
>
> I didn't have this issue until I did the Extended Temp Calibration routine.
> Radio is in the low 6000 s/n range - has all internal options except for 2m.
>
> Might have to send back to Elecraft for some brain surgery...
>
>