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.


  1. Q: For decoupling you mean the 2 4700uf or pf?

    A: The two decoupling capacitors for the RX ANT line are important, without them RF from the K2 made its way into this line and the K2 behaves erratically. They are both of value 4700 pF, one of them is one the K160RX board and the other close to P1 pin 7.

  2. Q: Now I wanna do the same thing for Rate/LOCK key to light when you have the VFO knob locked out and for the NB/LEVEL switch when the NB is on. Has anyone looked at adding lights for these 2 functions?

    A: The NB on signal can be found on the KNB2 board, but the VFO LOCK condition has no signal outside the microprocessor associated with it that I am aware of.

    Both of the additional LEDs that you propose are already indicated in the LCD display: VFO Lock with a blinking decimal point and the KNB2's with its own
    arrow. Thus the need isn't there in the same way as for the five that I have fitted.

  3. Q: I went ahead and put in the RANT LED too since I didn’t wanna reopen the front panel again. I don’t have the k160 board yet. I soldered from the 2.7/4v to the led thru the resistor 180ohms to pin 7. also put in one 4700 cap to a ground on the control board plug and pin 7 of the rf board. That was all. My KAF2 stopped being recognized after, sort of. It would still work you hold it and the LEDs for it came on and you could hear the difference in audio but the screen display would say not installed. The clock would also say not installed but in the menu it would recognize and show on or off. So after disconnecting the RANT LED from pin 7 on the front panel the KAF2 works normal now.

    Wow that was a lot, my question is do I need to isolate pin 7 from the AUXBUS by cutting the trace like I'm supposed to do on the 160 board when I get it? There's 2 red arrows with a space on your schematic I assumed that was a plug.

  4. A: In order to get a wire from the K160RX option to the LED on the front panel I had to use pin 7 P1 on the RF board. It is used originally for the AUXBUS,
    but since it is not used on the Front panel, the pin can be used here instead. But, _and this is important_, you have to cut the AUXBUS signal from the pin first. Otherwise the LED and everything else will load the AUXBUS so that the option boards that are controlled by the bus stop functioning, just like you have experienced.

    The 2 red arrows on the circuit diagram
    (http://www.qslnet.de/member/la3za/skjema/K2Leds_sch.pdf) are just the main plug P1 on the motherboard that mates with J1 on the Frontpanel board.

  5. Q: Well I cut the AUXBUS trace, have the LED hooked back up with the 4700 cap and no more KAF2 issues. Another thing that doesn’t have an indicator is the AGC on or off from pushing the pre/att and AGC buttons together. Any idea how to get that to light an LED? Trying to light up a K2 like a christmas tree here.

  6. A: There is an /AGC OFF signal on the K2 control board so in principle it should be possible.

    On the other hand AGC OFF is already indicated by a blinking digit in the display.

  7. Q: What about when you have the attenuator switched in? A light for that?

    A: There are relays both the the attenuator and the preamp (K16, K17), but just to read off the voltage off of one of the coil ends is not enough to get an unambigous indicator for the state. One will have to read both ends of the coil voltage and decode it. The K2's relay switching is quite complex with a clever utilization of a few lines for controlling many relays.

    On the other hand there are chevrons in the display for both ATT and PRE. so I don't see the great need for LEDs for this.

  8. Here's an idea for an indicator which I don't know if anybody will ever need or want, or even if it is feasible:

    A Red indicator in the RATE/LOCK button which will light up when the PLL goes out of lock. It should be driven from the RF board's PLL synthesizer chip, MC145170, and its LD output (pin 11) via a filter and a buffer. This indicator will only be lit when you tune too low or too high in frequency, and is only feasible if the K2 CPU enables the LD output.

    I have not checked if that it the case, it's a firmware thing for the K2.

  9. Q: Well finished the 160m option and the receive antenna works on and off I hear signals and don’t hear them but the led is backwards it's lit when off and off when rant is on.

    The schematic was wrong, the 4700 cap goes between 7 and 8 and the led goes to 7 not 9 if you want the light on not off with the rx antenna.

  10. Yes, I agree. I looked at the schematic again. Relay K2 on the K160RX module should be wired with pin 8 to ground and pin 7 should go out of the board in order to control the LED.

    By the way, this was how I planned it in 2005 when I first looked at this. Then I got the light wrong when I built it and changed the schematic. I must have missed on how to number the pins of the relay.

  11. Finally got it all working, heres a link.


  12. Congratulations, nice video on YouTube!

    See also more comments on the nature of these mods in the thread 'Flashy K2 on YouTube' on the Elecraft discussion list today.

  13. Nice illustrated implementation of four of the LEDs on AD7GR's page

    1. Just read your comment Sverre. Sorry I didn't see this years ago. I no longer have a web page but can supply the view behind the faceplace is anyone wants to see that.
      Ed - ad7gr

  14. There aren't so detailed instructions for how to fit the 5 LEDs above, but some may find tips in these documents that I built on when I worked on this:

    - Split/ Rit/ Xit LED indicator

    - K2 RIT-SPLIT LED Indicator Mod, Show & Tell Pictorial Supplement to the K2 RIT-SPLIT LED Mod Documentation

    - CW Zero Beat Detector (in key cap)

    1. The above links do not work any longer. Do you have updated links to these PDF documents?

    2. Try now, I should have fixed it now

    3. I get redirected to this page when i click the links above.


      Beklager, siden du forsøkte å nå finnes ikke.

      Dersom du forsøkte å nå en personlig nettside på webtjeneren folk.uio.no, er denne nå lagt ned. Brukere som hadde personlige nettsider på folk.uio.no er oppfordret til å flytte innholdet til en ny tjener kalt folk.universitetetioslo.no. Om du ser denne meldingen, kan dette tyde på at denne brukeren ikke har flyttet.

      Hvis det er viktig for deg at dette innholdet fortsatt er tilgjengelig, kan du vurdere å kontakte brukeren på en egnet måte for å undersøke om nettsiden er besluttet lagt ned, om innholdet ennå ikke er flyttet over, eller om innholdet kanskje har flyttet til en ny adresse. Brukeren kan nås per epost ved å putte brukernavn fra adressen før @uio.no, slik at dersom websiden har ligget på folk.uio.no/olanordmann/, kan du forsøke å sende til olanordmann@uio.no

      Vi minner om at både den gamle og den nye tjenesten er ment for kun personlig bruk. Dersom innholdet du forsøker å nå er relatert til jobb eller studier, er det muligens flyttet til et annet sted på UiOs offisielle nettsted, https://www.uio.no/.

  15. John WT5Y, has added even more lights to his K2. He cals it the K2 ghostlight mod and says it is a totally useless mod but the effect is neat. i agree!
    Read about it on the Elecraft list, and view it in action on YouTube.

  16. What would be the connection to the KDSP2 module for the XFIL – AFIL button LED? Has anyone done that?