26 May, 2011

Five LEDs in buttons for the Elecraft K2

The Elecraft K2 is quite a small transceiver, made for portable use. Therefore it has fewer indicators of status than many other transceivers. There isn't really much space for this on the rather small frontpanel. But I felt for a long time felt that it should be possible to put additional LED indicators on the K2 but I wanted to avoid drilling holes in the front panel. Here is a method based on using small LEDs in the keycaps, see info from W3FPR/KR5L, as you can always get replacement key caps from Elecraft.

On W3FPR’s recommendation I have used 2 mm LEDs of types HLMP6300 (red), HLMP6400 (orange/yellow), and HLMP6500 (green). They can be bought from Digikey as well as from ELFA in Northern Europe. The first two of the five LEDs that I have added can be connected from the front panel board without additional wiring to other boards.

This YouTube video shows the three first LEDs, the Zero-Beat Indicator, the Split Indicator, and the Audio Filter On indicator:

Here is a picture showing all five LEDS including those not shown above, the ones for TX ON and RX ANT ON:
The five LEDs are:
  1. Green indicator in PRE/ATT – SPOT button to show CW zero-beat. The low-power zero-beat indicator (old version here) drives the LED cathode directly with anode connected to the line that carries 4.0 V day/2.7 V night (emitter of Q2).
  2. Yellow indicator in A=B – SPLIT button to show that Split/RIT/XIT is on (requires firmware ver. 2.03d and IOC firmware ver. 1.07 and up). The 2 mm LED is not an ultra bright type so it requires a PNP driver transistor.
  3. Yellow indicator in XFIL – AFIL button to show that the audio filter is on. I have several times felt the need for this as I switched to SSB and wondered why the audio was so unintelligible, until I discovered that the audio filter was on. Here is how I did it:
    • KAF2 : 180 ohms from pin 7 of U2 controller to pin 4 of P2. P2 connector has been extended from 3 to 4 pins.
    • CTRL board: Loose wire from pin 4 of J2 (extended from 3 pins) to Front Panel board 
    • Front Panel board: Wire to cathode of yellow LED, anode connected to line that carries 4.0 V day/2.7 V night 
  4. Red transmit indicator in MODE – VOX button. It should be driven from a signal which is related to the 8T line, but unfortunately it is not present on the front panel board, only the controller board. Therefore a second loose wire is required between the boards.
  5. Yellow indicator in ANT1/2 – TUNE button to show that the RX ANT is on. Since relay K2 on K160RX has two sections which are in parallel for the RX antenna input, one part can be separated and used instead to switch the LED on and off. 
    • Relay K2 (K160RX) must be unsoldered and traces cut to separate pins 7, 8, and 9 from the RX antenna signal path. Then pin 8 is grounded, and pin  9  7 is routed to the LED on the Front Panel Board.
    • Wire from K160RX runs to pin 7 of P1 on RF board (was AuxBus, but this bus is not used on the Front Panel Board, so it can be cut)
    • Front Panel board: Wire from pin 7 of J1 via 180 ohms to cathode of yellow LED, anode connected to line that carries 4.0 V day/2.7 V night
The schematics can be downloaded here.

This was originally written on my old web page in 2005 and has been updated several times since then. This blog post was taken from that page in order to enable discussions relating to modification of the K2 in order to fit these and possibly other LEDs.  The first comments are all based on emails I have received with questions and comments, therefore you will see me as the author of these comments.