[Elecraft] Fool proof kill switch = deadman timer?

[Don Wilhelm]

Jim,

I think it could all be done with your Raspberry Pi idea.

The transmit state of the K3 can be indicated by the state of KEYOUT-LP 
on pin 10 of the ACC connector.  Since it is an open drain, you will 
need a pullup to determine its state.  It is grounded during transmit 
and open circuit otherwise.
When it is grounded, start the timer.  You will have to decide how long 
your transmissions will be.  Reset the timer with a positive-going 
transition of the KEYOUT-LP line.

If the timer expires, I would suggest first issuing a Power Off command 
to the K3 over the RS-232 connection.  If that fails, then more drastic 
action is required - like pulling the plug.

You can power the K3 back on by pin 8 of the ACC connector.  See Remote 
Power On at page 43 of the manual.

73,
Don W3FPR

On 5/29/2017 11:20 AM, Jim Miller wrote:
> In considering remote operation options I'm still struggling with how to
> implement a kill switch that is foolproof.