Introduction: January 2014 Build Night: EL Wire Nixie Tube

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Let's call this the EL-ixie tube for short.  This is one of H3 Laboratories' entries in the January 2014 Build Night With CoolNeon.

For those that don't know, see Nixie Tube is a vacuum tube primarily used in Russia and Eastern Europe to display a digit (usually), the same purpose as a 7 segment LED display.  However, in a Nixie Tube each digit is a separate filament that emits light when current is applied.  For more info, see Nixie Tube on Wikipedia.



We're going to make a replica of a Nixie Tube using EL wire to form the digits. Specific skills involved are soldering and optionally welding (for small tacks).

Take appropriate precautions when working with heat, solder, welding, scissors, etc.

Step 1: Materials & Tools

Materials:
  • (1) Arduino Uno
  • (1) CoolNeon EL Wire Shield
  • (12 to 15) feet of EL wire
  • (5 to 6) Wire coat hangers
  • (10) Female JST XH connectors
  • (20+) JST XH connector pins
  • (20) Feet 22 AWG black wire, solid core
  • (12 to 18) inches 1/4" black heat shrink tubing
  • (1) 80oz pickle jar or similar container
  • (1) 5" styrofoam cube
  • (1) 10k ohm potentiometer
  • (1) Breadboard
  • Electrical tape
  • Blue painter's tape
  • Black Duct or Gorilla Tape
  • Black Plasti-Dip
  • Fishing line (I used 4 pound test)
  • Copper tape
  • Jumper wires
Tools:
  • Soldering iron
  • Helping hands
  • Various small pliers
  • Wire stripper/cutter
  • Razor knife
  • Ruler
  • Forceps
  • Sheet metal edge crimper (optional)
  • Vise (optional)
  • (2) 6 to 10 inch pieces of 3/8" to 5/8" diameter steel rod (optional)
  • MIG welder (optional)
Software:
  • Arduino IDE
  • Blender, or similar 3D modeling program
  • Adobe Photoshop, the GIMP, or equivalent image editor
If your pickle jar is new and full of pickles, eat them.  Wash the jar thoroughly and allow it to air out; it will carry the pickle scent for a long time.

Step 2: Visualize

Each digit should be made from a single piece of EL wire, but some of them can be tricky to imagine this way.  Also, the connector end of the wire should be as low as possible to allow for more wire available outside the jar and going to the EL Wire shield.

Even with a large jar, the final result will be a tight fit.

First, I started by sketching each digit as a continuous line.  EL wire has a minimum bend radius of about 5 times its thickness; for any sharp corners I made a loop instead.  The loops will be addressed later.

Using pictures for reference, I modeled the pickle jar to scale in blender, then recreated my digit sketches as Bezier Curves.

The digits are stacked from front to back within the jar.  To minimize how much of each digit is obscured by those in front of it, I used a reference stack order from a real Nixie tube: 4, 5, 6, 7, 3, 8, 2, 9, 0, 1.  After that, each digit was sized to make it more visible.  This is why the 8 is noticeably smaller than the 0 and 9.  To help in this process, I positioned an isometric camera in front of the jar and rendered an animation the digits in sequence.

A Blender Add-on called Curve Tools calculated the approximate length of wire needed for each digit.  The total came to just under 10 feet.

Step 3: Coat Hangers

Use pliers to straighten the coat hangers.  These came with a white plasic sheath which got stripped off later.  Snip off the ends where they wrap around each other; it's not worth the time to straighten them.

This is where the vice/rod jig comes into play.  Place the rods in the vise vertically, about 3/16" to 1/4" apart.  Use the contact points of the hanger with the rods to create the necessary curvature.

To know what that curvature is, I rendered each digit in blender with a reference object for size: the green rectangle is 6" wide.  I then opened each image in Photoshop as I worked the bends; for my images a zoom of 97% resulted in the green rectangle being exactly 6" wide (your zoom will vary).

The hangers are for structure... they don't need the loops that will be in the EL wire.  Bend slowly, especially at the corners, otherwise the hanger wire will get fatigued and break.  This happened to the first 2 I made.  Try to keep the wire as flat as you can.

As you work, check the curvature by holding the wire digit against your computer screen (be careful not to scratch the screen).  Some adjustments can be made with pliers, others on the jig.  It is easier to adjust an existing curve than create a curve from a straight length.

Each digit also needs a leg.  I made the legs extend 7 1/2" below the lowest point of each digit.  Some of the legs (on the 3, 5 and 9) extend from a part of the digit that arcs upward, so bend them behind and then down.

Finally, notice that the 1 isn't a single line, but two.  This is done to give the one more area, otherwise it would appear dimmer than the other numbers.

On average, each digit took about an hour to bend.  1 and 7 were easiest, 8 was most difficult.  I estimate it would take twice as long without the jig.

Once each digit is done, if the coat hangers have a sheath like mine did, carefully cut it off.  I used small wire cutters.  Then I sprayed the bare wire with two coats of black Plasti-Dip.

Optionally, put tack welds on the digits that cross over themselves or have ends that butt against another part of itself.  For my digits this was 0, 4, 6, 8 (two tacks), and 9.  If you can't get them welded, a product like JB-Weld will probably work instead.

Step 4: Connectors

The connectors on the CoolNeon shield and the power inverter are JST XH style. They're rather tiny.

When researching connectors, a lot of places on the internet will simply identify a connector by its manufacturer (i.e, "JST")... once you find that, search for the manufacturer's site to narrow down exactly which style you need.  JST makes several dozen styles, and XH comes in many variants, from 2 to 20 pins and top or side entry (and of course male and female).

For this build, I cut and soldered a new pigtail for each digit.  I made the pigtails 12" long to make sure I had enough to get out of the jar and be able to plug them into the shield.

Step 5: EL Wire

I followed this Instructable for soldering the EL wire.  It's tricky to strip the jackets off and still have both angel wires remain.

I started by snipping the endcap off of one of the EL wire pieces, then soldered on the new pigtail.  Using 4 pound test fishing line, I tied the EL wire to the digit frame, then lashed the fishing line around at about 1/4" spacing.  At the loops and intersections, I made several revolutions with the fishing line to make sure the EL would stay in place.  When winding the fishing line, always keep it taut to the digit.

When I got near the end of a digit, I cut the EL wire to length, finished the lashing, and tied an end knot.  Use the forceps to put weight on the fishing line to aid in tying the knots.

I then began the next digit with the end I just cut off.

I ended up using two and a half of the 5 foot EL wire pieces... I lost a few inches due to failed attempts to strip the EL wire.

When all the EL wire is attached to the frames, mask off the pigtails and the parts of the digits that will be visible with painter's tape.  Be sure that the masking doesn't leave you with a gap where the loops cross.  Spray them with four coats of black Plasti-Dip, because you don't want the EL wire to glow through it.  When it's dry, carefully remove the tape; the Plasti-Dip doesn't form the greatest bond with the EL wire jacket, so be careful.

Step 6: Make the Base

The base started as a 5" styrofoam cube.  I made imprints on opposite sides of the cube with the jar opening to give me the correct size of the opening.  Using a rasp, I rounded the ends of the cube with the imprints into circles, then shaved the rest of the cube down to a cylinder using the ends as guides.  After a couple test fits, the cylinder fit easily inside the jar.  I then cut a groove on each side of the cylinder to allow the wires to pass through.

To get the digits to the correct height inside the jar, I cut about 2" off of the foam cylinder.  Consequently, I had to cut 1 1/2" off each digit's leg.

The cylinder was then wrapped with Gorilla tape.

Step 7: Prepare the Jar

I marked the groove positions on the base to the jar lid, then drilled them out with a 3/8" bit and ground the holes flat.

Mark the front position on the jar and the inside of the lid so you can match them later.

Most Nixie tubes are black in the back to make the digits more visible.  We did this on the jar by masking off the inside front of the jar and spraying Plasti-Dip inside.

Step 8: Final Assembly

Digits: check.  Base: check.  Jar: check.

Find the center of the base and mark it (I used a silver Sharpie).  The base's diameter is about 3 1/4", so each digit needs to be about 1/4" apart for them all to fit.  Mark the positions on the base as a guide.

Press each digit's leg into the base, making sure they are straight and plum. Some adjustment can still be made by bending the leg.  Work from front to back or back to front.  I ended up bending a couple of the legs to give more stable positions in the base.

With all the digits in the base, run the connector wires into the grooves on the base.  Which groove the wires go to depends on which side it is closer to... I think I ended up with 4 on one side and 6 on the other.

Tape the connector wires into the grooves to keep them in place.  Then push the connectors through the holes in the lid that matches their side (remember to match the jar front with the lid front).

Carefully push the digits into the jar.  It'll be a tight fit, so expect to coax them in.

Screw the lid onto the jar.  You can gently pull the connector wires to get the base to sit flat on the lid.

The lid is now the bottom of the EL-ixie Tube.

Step 9: Arduino Sketch

The Arduino sketch is very simple.  It sets up digital pins 4 through 13 as outputs to the digits, and analog pin A0 as an input (the 10k ohm potentiometer).

// the potentiometer is on analog pin 0
const int pot_pin = A0;

// this array sets up the digits pins used for the digits
const int digit_pins[] = {4,5,6,7,8,9,10,11,12,13};

// the number of digits
const uint8_t digit_count = 10;

// stores the new index into the digit_pins array (0 to 9) as read from
// the potentiometer
int v = 0;

// this incrementor is used a couple times
int i = 0;

// stores the current digit value
int x = 0;

// an obviously out of range digit to start with
int last = 20;

void setup() {
//	Serial.begin(9600); // for debugging
	delay(200);  // let the Serial start up

	// loop over the digit_pins array to set their pin mode
	for (i = 0; i < digit_count; i++) { 
		pinMode(digit_pins[i], OUTPUT);
	}
	
	// set pin mode fotr the potentiometer
	pinMode(pot_pin, INPUT);
}

void loop() {


	x = analogRead(pot_pin);

	v = (int) (x / 102.3);


	// only do something if the value has changed.
	if (v != last) {

//		for debugging
//		Serial.print(x);
//		Serial.print(' ');
//		Serial.println(v);
	
		// loop over the array; turn each digit on or off as appropriate
		for (i = 0; i < digit_count; i++) {
			if (v == i) {
				// turns a digit on
				digitalWrite(digit_pins[i], LOW);
			}
			else {
				// turns a digit off
				digitalWrite(digit_pins[i], HIGH);
			}
		}
		
		// update the value
		last = v;
	}
}