[Elecraft] A better way to add a SPLIT/RIT/XIT LED

[Wayne Burdick]

Using the 10th LED on the bar graph as an optional, highly visible
SPLIT/RIT/XIT status indication is a compromise, as I mentioned in a
previous posting. Some of you really disliked the idea, which encouraged
us to try to come up with a different solution. Here it is--let me know
what you think.

A few K2 owners (including Bob Locher and Jerry Bliss) had suggested
adding their own small, round "SPLIT/RIT/XIT" LED to the front panel.
The problem with this idea was that we lacked an available drive line
for the LED. But it turns out there *is* an available drive line--some
trickery is all that's required.

On the K2's Front Panel schematic, you'll notice a logic line called
"SRDOUT". This line is used to set up data for the two 8-bit shift
registers (FP-U3 and FP-U4). It is normally set to 0 volts between shift
register updates, but I just modified the firmware to set it to 0 or 5
volts between updates depending on the SPLIT, RIT, and XIT status. By
adding a resistor and capacitor, this becomes a direct drive line for a
high-efficiency LED. In my case, I used a high-brightness miniature
("T1") size LED, a 1.8-k resistor, and a 100-uF capacitor. The resistor
does double duty: it sets the current for the LED, and forms a low-pass
filter with the capacitor. 

Further, it should be possible to control the brightness of this LED the
same way as the bargraph: by using the "DAY/NIGHT" drive line as the
return for the LED. And it can be turned off by setting GRPH to OFF.

I know that noone wants to drill a hole in thier K2 front panel, but
this would allow you to put the LED where you want it. I'm planning to
mount mine to the left of the RIT button and above the RATE button. This
is the only unused space on the panel, and it makes sense to put the LED
here since it's not far from the A/B/RIT/XIT annunciators. Another
possibility might be to put a red LED near the bottom edge of the LCD,
but with no hole: if it's bright enough, it will cast a nice red glow
near the A/B annunciators. I haven't tried this yet.

There are details to work out, such as providing blinking or
non-blinking or OFF selections, an option to apply it to RIT and XIT as
well as SPLIT, etc. But this will definitely be a new feature of the
next K2 firmware revision (the rev that ships with the KPA100 option). I
have already tested the new indicator LED, and it's a keeper!

I'd like to thank the critics of the original idea  ;) 

73,
Wayne