[Elecraft] [K3] K3 driving KK1L band decoder

[Joe Subich, W4TV]

The PS2501-4 in the inputs of the KK1L band decoder are opto isolators.
Pull up resistors will be required in the K3 in order to provide drive
to the LEDs in the optos.

> My KK1L board (built in 2006) seems to be loading down the K3 band
> outputs.

The K3 band data outputs are open drain - they can not be "loaded
down" as they do not source voltage.  Note:  the KK1L design uses
3K3 Ohm series resistors to limit current to optos.  Depending on
the sensitivity (current transfer ratio) of the PS2501-4 you may need
to reduce the resistance of those resistors in order obtain enough
current through the LED.

73,

    ... Joe, W4TV


On 9/6/2012 12:05 AM, Ethan Miller K8GU wrote:
> Is anyone else running a K3 with a KK1L band decoder?  The K3 manual
> states that "earlier K3s may require external pull-up resistors to 5
> vdc."  Did you need to do this?  My KK1L board (built in 2006) seems
> to be loading down the K3 band outputs.  Before I add the pull-up
> resistors, I just want to make sure that this isn't a sign of
> impending doom...
>
> Thanks and 73,
>
> --Ethan, K8GU/3.  (K3 S/N 6714, TS-930S S/N 5010245)
>