[Elecraft] K2 RF board resistance check - RYCOM

[Lyle Johnson]

> Well, we located it there - but that is not the question.  The
> real question is 'how does DC voltage get to RYCOM?' ...

This puzzled me for a while, too, when I first looked at it a couple years
ago.  But thinking about what's going on made it pretty clear.

All the relays have their "other" terminal tied to individual PIC pins.

To turn on a given relay, you set ALL the relay pins to a given state, say
+6V, then pull the "other" pin of the relay you want to set to 0V.  Only
that relay will trip; the others aren't getting enough current.

To set the relay the other way (assuming a bistable latching relay with a
single coil) you set all the relay "other" pins to 0V, then pull up the one
you want to trip to +6V.

This only works, of course, because there are multiple relays involved and
they are all latching relays.  Look at the KAT100 manual for a method that
looks a bit more familiar...

-Lyle KK7P