[GreenKeys] FSK converter madness

[Harold Hallikainen]

Thanks for the comments!

Voltage drive would make it easy since each receiver can "bridge the
line." But, that requires a driver circuit and loop supply for each
receiver (printer). Messy!

> Things were complicated by irv Hoff's insistence that you should always
> be able to plug in a keyboard and printer in series into a loop and
> have everything work.

I agree with Irv! I have patch boxes with 1/4 inch TRS shorting jacks.
Each patch box has its own loop supply, and I can just plug whatever
equipment I want into the loop, and everything works. The TU is just like
any other piece of equipment. It just gets plugged into the loop.

> I did some work on a "leg combiner" which could
> take a keyboard and printer in series and tell the difference between
> signals generated by the keyboard and signals coming from outside.

In the DSP TU, the loop current sample always drives the DDS AFSK
generator. It does not matter whether the loop is interrupted by the TU or
something else in the loop. However, with Keyboard Operated Send, it's
important to know whether the TU is interrupting the loop or something
else is (like a keyboard or TD). Otherwise, a received space would put us
into transmit. I handle this by disabling the KOS whenever the TU is
interrupting the loop and for a few milliseconds after the TU stops
interrupting the loop.

THANKS for the comments!

Harold
https://w6iwi.org/rtty/DspTU2/