[Elecraft] K3S with more than one device on the Band Data signals

[Jack Brindle]

As I recall, it is a standard LS TTL style open-drain driver, which means it has a fan out of about 10 LS loads. You should be able to connect several devices. Be sure they do not have pull-ups that are connected to higher that 5 volts (some band decoders have pull-ups to 12V). The K3 has internal pull-ups to 5V, so having 12V on these lines will subject the K3 to 12V. The internal pull-ups will limit the current, but if the K3 is off when the decoder is on, you could get damage or even false powering of some of the K3 internal components.

False powering means that the component is actually powered through an IO port instead of its main supply line. This is a very bad situation that can damage the part since it is powered incorrectly. It is also maddening to debug since the part (possibly a processor) seems to be working when it should not be and can actually do some very strange things.

73!

Jack, W6FB


> On Mar 10, 2017, at 2:38 PM, NOEL POULIN <ve2fww at globetrotter.net> wrote:
> 
> Hi to all,
> I am on the way to connect a Bandpasser2 (band data mode) on a K3s.
> Later I would like also to connect a band decoder on the same radio to switch coaxial stubs.
> I wonder if the K3s can handle more than one device connected to the Band Data signals.
> I suppose that Elecraft band output is probably designed to drive one decoder and this decoder is designed with current maximums for each port.
> I would appreciate comments and good tips about that fact...
> Thanks
> Noel
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