[Elecraft] K3 band data lines

Mon Feb 8 15:48:03 EST 2016

I've done an experiment. 
I got a 7805 and powered it from a separate power supply. 
The negative of the 7805 is connected to the GND of the arduino.
If I connect the 5V from the 7805 to one of the digital inputs, the
arduino powers up and executes my program, lighting up the leds as
expected. If I add the diodes as suggested by Jack, this doesn't happen
anymore. But I can't read the 5V from those lines anymore, either. 

I'm now trying to figure out how to replicate the BAND line driver
circuit that is mentioned on Cady's book on my breadboard. Not sure if I
can simulate the mosfet by just shorting that line to ground between the
2.2k and the 220 ohm resistors. In any case, in this configuration I
have to use the arduino internal pullups, and if I disconnect the
external 5V power, I still measure around 1.3 V in the place where there
would be the K3's 5V, if I have the arduino still powered up. 
Also, the logic signal of the lines seems to be reversed. 

I'm seriously thinking that the safest way for me to proceed at this
point would be an optoisolator. 

Pf

>>>>> "Bill" == Bill Frantz <frantz at pwpconsult.com> writes:

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

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

    Bill> 73 Bill AE6JV

    Bill> 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?
    >>> 
    >>> -----------------------------------------------------------------------
    >>> Bill Frantz        | I don't have high-speed      | Periwinkle
    >>> (408)356-8506      | internet. I have DSL.        | 16345 Englewood Ave
    >>> www.pwpconsult.com |                              | Los Gatos, CA 95032
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    >> 
    >> 
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-- 
Pierfrancesco Caci, ik5pvx