Spektrum DX6i Logo Bar with Knight Rider LED Chaser Effect

Spektrum DX6i Logo Bar with Knight Rider LED Chaser Effect




I have been looking at the other posts regarding backlight mods in Spektrum DX6i transmitters.  The DX8 comes fully backlit, logo and display.  This mod is solely for the logo bar backlighting.  So if this is what you’re after:

Whoaa there.  Pump the brakes.  There’s an updated version of this article here.  It’s recommended you read this write-up first as some of the foundation is presented here.

Here’s a hint: The other write up is Arduino-based.


Then these are the steps I used:

Constructing a 5 LED chaser with an NE555 and CD 4017.
The diagram is here: http://bit.ly/schematicNE555CD4017IC
The CD4017 pinouts are here:http://bit.ly/CD4017pinouts

EDIT: Correction, in the video at the bottom of this page I mention a 68Ω resister (at 2:18). That should be 68KΩ. The diagram is correct.

Things you will need:

  1. 1x NE555 Bipolar Timer http://bit.ly/NE555
  2. 1x CD4017 Decade Counter http://bit.ly/CD4017
  3. Schmart Proto board (or equiv) http://bit.ly/SchmartBoard
  4. 5x 5mm x 2mm rectangle LED (color of your choice.  I used orange to match Spektrum)
  5. 5x 91 Resistor (1/4W)
  6. 1x 1K Resistor (1/4W)
  7. 1x 68K Resistor (1/4W)
  8. 5x 2N2222 transistor http://bit.ly/2N2222
  9. 11x diode capable of clocking ~6Vdc
  10. 1x 1µF Electrolytic Capacitor (10V min) http://bit.ly/1uFCap
  11. 8 PIN DIP socket
  12. 16 PIN DIP socket
  13. Wire
  14. Solder and solder Iron
  15. A breadboard to do proto-work unless you have skills

I put this set up in my Spektrum DX6i for the logo bar LED that they saw fit to omit.

Let me be clear. The steps in this write up are what worked for me. They may not work for you. That is not my problem. These steps will very likely void your warranty. In addition, these steps will also at a minimum cause you grief from the flying officials at your club or fly-in. Those types play by the rules and it’s very unlikely they will be impressed with your low voltage electrical prowess.

I take zero responsibility for the results of your proceeding with these modifications. I make no warranty claims toward the repairs should you render the transmitter inoperable. In other words, perform these steps AT YOUR OWN RISK.

Phase 1:

Let’s get hacking.  First thing, crack the Tx halves apart and remove the RF module, button/buzzer PCB plus the throttle and elevator trim assemblies.  From the front, wedge an LED in each bar groove one at a time.  Take an X-acto knife and score or scratch a line in the recessed groove at the low point of the LED.  This will become the bottom of your cutout.  Do this for each groove.

Take your time with this part.  Your patience will pay dividends in the end, so don’t rush things.  Carefully cut out the recessed plastic so that the LED can be pressed into the opening you make.  It should be quite snug.  Some of mine fit better pressed in from the front, others from the rear, so when you’re fitting things make sure to try from both directions or you may end up with gaps and loose fitting LED elements.

After you have the five cuts completed place the LED’s.  I made mine flush with the front of the Tx plastic. You could have them protrude, not sure how it would look though. Make sure to keep the anode and cathode leads in the same orientation as you’ll be seeing cross-eyed before this project is done.  Take some hot glue and pump it in all around the rear of the LED’s and plastic Tx body.  Get in between the LED leads so they can’t easily short out.  You’ll be bending these around as you fit the wires into place so be liberal with the glue.

Phase 2: Are you regretting this yet?

Wake up your inner nerd and assemble the IC board.

I strongly recommend you prototype this on a breadboard.  These are dirt cheap on eBay and help you clearly see the design layout.  As you proto it out you can see places for circuit placement and optimization.  Experiment here before you get into the soldering stage on the Schmartboard.

Take a break here.  It requires concentration and patience.

Basically, you’re taking the +6Vdc from the Tx batteries and running it through the NE555 IC to get an output pulse.  The frequency of that pulse is determined by the resistors used between it and the the +6Vdc, along with the capacitor.  If you hooked up an LED to the output of the NE555 you’d see it strobing rapidly.  It’s this strobing/pulsing that creates the on/off event for the next IC, the CD4017.  Since you have a pulsing output, the CD4017 will take that pulse and pass it through 10 outputs in a linear order.  This gives you the sequencing needed to build the chasing effect.  In short, the CD4017 distributes the NE555’s pulse across 10 outputs, hence the CD4017’s name, decade counter.  Hmmm, interesting, right?

OK, so you followed the schematic and have a nice breadboard worked up.  Great!  We’ve separated the men from the boys.  Lot’s can go wrong, and probably did.  Take your time.

Phase 3: TheNE555 wiring explained

So you worked out the kinks but do you know what’s actually occurring?  I can fill in the blanks for you.  You’re taking the +6Vdc and connecting it to NE555 P8.  P8 connects to P4. P8 also connects to P7 through the 1KΩ resister (R1).  P7 then connects to P6 through the 68KΩ resister (R2).  P6 also connects to P2.  P2 connects to P1 through the 1μF capacitor (C1, polarity sensitive).  P1 connects to ground.  P5 is open.  All of this gets up the pulsing output from P3.  We’ll take that awesome pulsing P3 output and connect it to CD4017 P14.  Ahhhh, NE555 wiring complete.

Phase 4: The CD4017 wiring explained

So we know the NE555 makes the on/off pulse and that the CD4017 will take each of those pulses and increment it out the 10 outputs in linear (zero through nine) fashion.  Great, except the outputs are numbered differently from the pin numbers.  Your head may have already exploded in the breadboard phase but if not, it may now.  This sucks.  Straight up crappy numbering of the outputs.  Take another look at the CD4017 pinout image above.  Notice those “output Qx” labels?  Yea, those are the sequenced output pins.  So basically, the CD4017 will fire the outputs like we want in 0-1-2-3-4-5-6-7-8-9 order BUT that happens out physical pins 3-2-4-7-10-1-5-6-9-11.  WTF?  That’s worse than the firing order of an old V8.  Just keep the image handy and reference it often.

OK, P16 connects to +6Vdc.  P15 and P13 connect to ground.  Here the wiring really gets wonky.  Since it fires Q0-Q9, we want it to pulse all 5 LED’s and then return back.  So we need to double up on the outputs.  We want LED 1 to fire when Q0 and Q9 fire.  LED 2 fires on Q1 and Q8, LED 3 fires on Q2 and Q7, LED 4 fires on Q3 and Q6 and LED 5 fires on Q4 and Q5.  This gives the chase effect a little pause at each end because LED 1 and 5 fire twice, back-to-back (think about it, Q5 fires after Q4 and on the return, Q0 fires after Q9 as the counter cycle loops).

You still with me?  It gets more fun.  Because the input source voltage is so low the LED’s are rather dim.  This is actually a combination of the low voltage and short illumination time (and quite possibly the lead-in resistors but I couldn’t find a suitable alternative).  Enter the transistor.  The transistor acts as a gate to pass a higher voltage when triggered by a lower voltage.  More on this in phase 5, but before we get too far ahead of ourselves we need to introduce some diodes to the mix.  Ten of them at this point to be exact.  This is because the outputs are doubled up and this causes the active-pulsing output, say Q8, to fight with it’s inactive paired up Q1.  The diode is a one-way device so the Qx outputs don’t “see” each other.  Wire up each output Qx to a dedicated diode, being polarity conscious, of course.

Phase 5: The mighty transistor

Without doubt, one of the most underappreciated inventions.  Ever.  After you wire this up, blow your mind with the fact they cram billions – with a capital B – transistors into computers.  The ports on a transistor are called emitter, base and collector and connect as the +6Vdc output , trigger and +6Vdc input respectively.  The +6Vdc input is hung until the base is triggered.  That trigger is from the diode outputs.

So we have ten outputs paired up in two’s, and each output in a given pair are diode isolated and then used to trigger their shared transistor.  Ten diodes, five transistors.  Wire the transistors so the output of CD4017 Q0 and Q9 connect through their diodes to the base on transistor 1 (T1).  Q1 and Q8 wire through their diodes to the T2 base and so on.  Basically, each T base pin has the output of two (specific) diodes connected.

Connect the collector of T1 through T5 to +6Vdc.  You’re almost there.

Phase 6: Bringing the PCB together

The transistors each have an emitter.  Connect the emitter of T1 through T5 to resistors R3 through R7, one each.  Take the other end of the resistors and connect them, again one each, the cathode of the LED’s.  Common up the anode LED leads and ground them.

Phase 7: Void that warranty and find some power

Since you already pulled the two trim assemblies, button/buzzer board and RF module go get a hacksaw.  Seriously.  That buzzer you hear beeping at you in your sleep is in the way.  Mark the polarity and unsolder the buzzer.  Now hacksaw the end of that PCB off right above the screw hole.

To power this you can pull switched +6Vdc (or whatever the batteries have left) from the BAT solder dot.  This will toggle anything with the main power switch.  Grab ground from the ON solder dot.  I used a servo extension wire so I could disconnect it.  There is also a diode (D11) from + input on the PCB you made (not the one you cut) to protect the Tx from anything backfeeding, should there be any issues.


Hot glue that PCB in the Tx body.  I found the most space is beneath the aileron/elevator gimbal.  Close it up AND YOU’RE DONE!

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