[Elecraft] K3 band data lines

[Bill Frantz]

The band input line pins are set up as input on the Arduino. As 
such, they are high impedance, so I don't think there is any way 
to drive them from the Arduino (short of changing the 
program/sketch). I normally leave my switch controller powered 
on with the K3 powered off, and have not experienced any problems.

If there were other things in the shack driving the lines, there 
might be a over voltage issue for the Arduino, but I think there 
would also be issues with the K3 driver circuitry. (One drives 
high, one drives low and lots of current flows.)

73 Bill AE6JV

On 2/7/16 at 10:52 AM, jackbrindle at me.com (Jack Brindle) wrote:

>This can work. But it can cause problems as well. You should 
>add isolation in the form of either small diodes (cathode 
>towards K3) or small resistors (maybe 100 ohms).
>The problem is that if the Arduino is left powered on when the 
>K3 is off, the Arduino can actually leak power into the K3 
>through these connections and can actually power parts of the 
>K3 (as in parts, but not all, of the cpu). This false power can 
>lead to other problems, which is why we suggest the isolation diodes.
>
>The second thing is to remember that 60 meters is coded as all 
>zeros. The K3 has pullup resistors on the band lines, which 
>will pull the band lines to whatever Vcc happens to be at that 
>time. When the K3 is off, Vcc is zero, which will be the value 
>of the band lines (i.e. not high-impedance). Thus when the K3 
>is off, you will see a band selection of 60 meters. KPA500 
>users see this as the KPA500 switches to 60 meters if it is 
>left powered up after the K3 is switched off.
>
>Good luck with the project!
>
>- Jack, W6FB
>
>>On Feb 7, 2016, at 9:47 AM, Bill Frantz <frantz at pwpconsult.com> wrote:
>>
>>I have built a similar switch controller. If anyone wants a copy of the details, please ask.
>>
>>Specifically:
>>- Just connect te band lines directly to the Arduino inputs. It works fine.
>>
>>- Don't know about cross band split. However K 3 power off and 60M look the same.
>>
>>- I don't bother. I don't change bands while transmitting. I'm not sure if the K3 even supports it.
>>
>>73 Bill AE6JV
>>
>>
>>On 2/7/16 at 3:38 AM, pf at tippete.net (Pierfrancesco Caci) wrote:
>>
>>> Hello,
>>> I'm trying to make my own interface between the band data lines on the
>>>  accessory connector of the K3 and the remote antenna 
>>>switch.  I have a few questions that I hope you can help me with:
>>>   - is it safe to just poll the band lines with the arduino 
>>>digital input
>>>  pins? I understand that my K3 is new enough to have the internal pull
>>>   up resistor. Should I put an isolation device inbetween?   
>>>- does the band data as provided by the K3 always track the 
>>>TX VFO?
>>>  Should I expect some weird situation if I ever try to do cross-band
>>>   split?   - should I bother with asserting TX Inhibit and 
>>>keep it set for a few
>>>  milliseconds when I detect a band switch?
>>
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