[Elecraft] K2 RF board resistance check - RYCOM

[Bob - AG5Q]

RY COM is only connected to the relays. The relays are switched to the ON position when the current flows in one direction and to
the OFF position when current flows in the opposite direction.  After the switching is done, no current is required to hold the
relay since it latches internally, so the current is programmed to zero. This saves a lot of current, which reduces power
dissipation and reduces the load on the battery.

The outputs of U1 are programmed in push-pull.  To program a particular relay, its driver output is set to either a logic ONE or a
logic ZERO, depending on which way the current should flow, and all the other relay drivers are programmed to the opposite state.
All the current flows through the designated relay and switches it, but this same current is divided among  the other relays and
there isn't enough current through any one of them to cause them to switch.  After the relay is switched (in a few milliseconds),
all the driver outputs are set to the same logic state, so no current flows through any of the relays.

73/ Bob - AG5Q


----- Original Message -----
From: "Don Wilhelm" <w3fpr@peoplepc.com>
To: "Thomas Beaudry" <k8la@arrl.net>; <elecraft@mailman.qth.net>
Sent: Sunday, July 27, 2003 9:28 PM
Subject: Re: [Elecraft] K2 RF board resistance check - RYCOM


> Thomas,
> Well, we located it there - but that is not the question.  The real question
> is 'how does DC voltage get to RYCOM?'  It seems that the only path is
> through another relay coil or through capacitors.  Perhaps the pulse through
> the caps is enough to set or reset the relays, but I just don't know.
> 73,
> Don W3FPR