Chua Circuit Chaos Easy Build

Chua Circuit Chaos Easy Build - No Inductor

Here's a phase portrait of a beautiful single scroll chaotic attractor from my oscilloscope! I was able to also confure up a multiple scroll attractor and also a teeny-tiny double scroll illustrating the classic chaotic circuit output. A Strange Attractor is when a bounded chaotic system has some kind of long term pattern that isn’t a simple periodic oscillation or orbit.



Here is how two superimposed attractors form the famous double-scroll attractor:

Here is a video:;

Nice Mobius strip attractor, the only possible attractors in this pattern are limit cycles:

Here is a multile limit cycle attractor as it adds more ovals to become a single scroll chaotic attractor.

My oscilloscope settings for my "newer" scope.

There is a progression from steady state to limit cycle to chaos and bifurcation. Steady state is a dot; an oval signifies a 1 period limit cycle; multiple overlapped ovals show 2 or 3 or 4 limit cycles; once the ovals are plentiful and have a sort of inverted rounded pyramid shape (like mine above) it's a single scroll chaotic attractor. 

The famous double scroll chaotic attracot can have two appearances depending on your setup and equipment: the single chaotic attractor with some extra, lighter ovals underneath it; or sort of a figure 8 shape.



The circuit build is towards the bottom of this post.

Chua's Circuit is basically an oscillator that outputs waveforms that never repeat: chaos! Chua's Circuit is the simplest circuit that can output real chaos. Chaos in the form of a double swoosh set of circles on an oscilloscope screen. This waveform is called an attractor, which demonstrates chaos in a continuous time dynamical system...I like the idea of a waveform generator / oscillator that never repeats. A continuouly evolving, periodic output that never repeats: chaos!

What defines chaos in a system like this: extreme sensitivity to initial conditions; cause and effect are not proportional; and it is nonlinear.

This circuit will also display bifurcation: small, smooth changes lead to a sudden huge change in the system. Tuning a silent radio with a knob that you're barely moving, you keep trying to nudge the timing knob and you all of a sudden loud music starts playing. Or slowly as possible applying more pressure to a mousetrap until it springs shut. The straw that broken the camel's back.

We will make it less simple by replacing the supposedly hard to find, but definatly hard to choose thet correct value for inductor-with a gyrator circuit which acts as an ideal inductor. Just a couple extra cheap parts and it still works.



First off when looking at schematics to build your very own Chua Circuit you need to ignore 99% of the useless schematics out there. The schematics you'll see are for explaining this circuit, but not building it. Here is an example of the classic circuit...that doesn't tell you what you need to know:

You will see on the left side an "L". That denotes a simple 18mH inductor. These inductors are sort of hard to find. You could try and swap in and out various 18mH inductors with less than 30 ohms resistance and play around with that. They are pricey and might not be exactly the spec your circuit needs to operate. We will replace the "L" with a TL082 op-amp acting as a gyrator inductor simulator. It works like an inductor (in this circuit at least) and operates ideally. Simple! The gyrator is known as "The Fifth Linear Element" and basically couples voltage from one source to the current from a different source...and then does the same with the remaining devices' current and voltage. Once working I plan on replacing the gyrator with an actual inductor, since I just found a pile of different sized ones in a drawer. An actual inductor will add parasitic resistance that will have to be counteracted in the circuit.


You will see on the right side of the circuit "NR". That is Chua's Diode...except that there is no such thing as a Chua Diode. You can't buy one in a store, you have to make it. Luckily we can make our own Chua Diode using a second TL082 op-amp. 

There are versions of this circuit which leave the inductor and replace this Chua diode with a memristor, but it involves more potentiometers (knobs) than this way. You will soon learn of my hatred for wiring pots. Anyway Chua’s diode has nothing in common with  a diode; it has a non-linear voltage-current characteristic that makes the oscillator output “unrepeatable”.

Then we'll add in some resistors, capacitors (use metal film, not carbon, for best results), a couple of knobs (potentiometers), and a DC power supply instead of two 9v batteries oddly wired together in many of the circuit designs.


The only other fancy "thing" I've made has been a scanning tunneling electron microscope. This project is very similar in that it used op-amps and the x, y and z inputs on an old oscilloscope. Because this is low voltage you can use a PC computer-based oscilloscope without blowing stuff up-as long as it can handle 9vDC. However if you use a modern fancy standalone digital oscilloscope the swooshing waves of the the output (a Chaotic Attractor) turns into swarms of ugly dots that are really hard to interpret.


After the annoyance with the schematic above I became annoyed with the build schematics I found for one simple reason: they show 4 triangles that are op-amps. So, I assumed I needed four op-amps, but the TL082 is a double-op-amp: each black box with 8 legs (pins) sticking out actually has two triangles inside of it. Four triangles on the schematic = two TL082 op-amps. Nice.

Also, the schematic didn't label the triangles as being A/B pairs. Which I'm not used to. So, when I scribble out my diagrams I'm labeling them A and B. One A/B triangle pair is a single TL082. This will make total sense once you read the next few lines and check the pinouts.


So, the first thing to get straight is the op-amp circuits. While it might look like we'll be using four TL082 circuits we're really only using two of them!


Here's a simple pinout that is for a different op-amp, but which has the same pinout as a TLN082, but it's drawn better. It's much easier to see how each little TL082 microchip is actually a double op-amp. One amp is "A" triangle and the other is "B" triangle. Look at this and the build schematic will make sense:

You can see that there is an "A" op-amp, and a "B" op-amp.

A = pins 1, 2 and 3.
B = pins 5, 6 and 7.

Pins 4 & 8 power the entire TL082 (both A and B together).

Inverting inputs are negative (-) inputs.
Non-inverting inputs are positive (+) inputs.

So, in the schematics for Chua circuits (done without an inductor, using a gyrator instead) you will see four triangles. They represent the A & B portions of only two TL082 op-amp circuits.

You will see two triangles near each other, and two other triangles paired up on the other side of the schematic. Each pair of triangles near each other represents a single TL082!

You must treat each triangle as an A or B regarding pins. Decide which triangle in a pair is the "A triangle" and which is the "B triangle".

Anything that goes to the A triangle will only use pins 1, 2 and 3.
Anything that goes to the B triangle will only use pins 5, 6, and 7.
Pins 4 and 8 get the input from your power supply/batteries. It doesn't really matter which triangle those go to, but for simplicity we'll put the 4/8 power to the "A" triangles.

So, on the left side of the circuit where we are not using an inductor, but building a gyrator instead we have two triangles.



Left Side of Schematic-Gyrator Inductor Simulator

Triangle A is on the right:
Pin 1 = OUT A
Pin 2 = Inverting Input A (negative -)
Pin 3 = Noninverting Input A (positive +)
Pin 4 = Negative Power Supply input
Pin 8 = Positive Power Supply input

Triangle B is on the left:
Pin 7 = OUT B
Pin 6 = Inverting Input B (negative -)
Pin 5 = Noninverting Input B (positive +)

There, now you have all 8 pins on one of the TL082 op-amps wired up!




Right Side of Schematic-Chua Diode

Triangle A is on the right:
Pin 1 = OUT A
Pin 2 = Inverting Input A (negative -)
Pin 3 = Noninverting Input A (positive +)
Pin 4 = Negative Power Supply input
Pin 8 = Positive Power Supply input

Triangle B is on the left:
Pin 7 = OUT B
Pin 6 = Inverting Input B (negative -)
Pin 5 = Noninverting Input B (positive +)

There, now you have all 8 pins on your second TL082 op-amps wired up!

BREADBOARD WIRING

Wire Jumpers:

c18-c24
e18-f19
g19-g25
e21-f21
he21-h24
d23-d29
e29-f29
i26-i32
j28-j29
c25-c31
h32-h39
h42-h49
g48-g49
i48-i54
e49-f49
h52-h56
c48-c52
d49-d53
b51-b55
a55-a56
f56-f57
d3-g3
j50 to right power right outside
left power rail inner to b3
left power rail outer to a54
left power rail outer to a26
j50 to right power rail outer
j10 to right power rail inner
j51 to right power rail inner
left power rail outer to a10
j23 to right power rail inner
left power rail inner to b3
i3 to right power rail outer
left power rail outer to a54
left power rail outer to a26
j50 to right power rail outer
j10 to right power rail inner
j51 to right power rail inner
left power rail outer to a10
j23 to right power rail inner

TL082 Chips
Top of chip (with half circle dimple) pins 1 and 8: e23 and f23
Top of chip (with half circle dimple) pins 1 and 8: e51 and f51

Resistors
220 b10-b13
220 i10-i13
1k b21-b24
2.2k b25-b28
1k h25-h28
100 g26-g29
3.3k i39-i42
22k a48-a51
22k c53-c56
3.3k left power rail inner to a52
3.3k i39-i42
2.2k g50-g53
2.2k g54-g57
220 j53-j56

Capacitors (film metal not ceramic)
10nf j42 to right power rail outer
100nf a21-a25
100nf j26 to right power rail outer

LEDs
left power rail inner to to a13
j13 to right power rail outer

Batteries
9v Battery 1: red positive to c3 / black negative to c10
9v Battery 2: red positive to h10 / black negative to h3

Ground wire for oscilloscope probe ground clips
right power rail outer (last bottom, right hole)

Oscilloscope probe to leg of capacitor sticking out of hole j26
Oscilloscope probe to left of capacitor sticking out of hole j42

Potentiometers/Trim Pots
Pot 1: middle pin b31 / either other pin left power rail innter / 3rd pin unused
Pot 2: middle pin f39 / either other pin f42 / 3rd in unused

The left side of the breadboard usually has positive and negative...but in this circuit both columns are negative.

The right side of the breadboard is positve on inner column, negative on the outer column closest to the edge of the board.

10k linear potentiometers are recommended because they're easier to turn and are more precise. I used 10k trim pots with are less precise and have to be turned with a screwdriver--bad choice!

Connect the two halves of the circuit with some wires, knobs, outputs to oscilloscope or a USB PC computer-based oscilloscope (with a huge resistor on the outputs so you don't fry your computer or digital scope) and you're good to go. I have real oscilloscopes that are analog/tube and can handle high voltage inputs. Your digital and computer PC scopes might blow up if you try and put more than 3v into them. Read your specs. This thing basically has two 9vDC input spots that may total 18vDC if you mess things up.

As always my nemesis is the humble potentiometer (volume knob). On some projects you need to use all 3 pins, but some only 2...and the circuit schematics almost never tell you which. Is it a voltage divider (might be 3 pins) or is it a current adjuster (2 pins?) or is it a volume knob for audio (3 pins?) or a variable resistor (2 pins!)?

************On the most popular "fritzing" diagram for Chua circuits they show 3 wires going to the potentiometers but in the explanation 8 pages later they state that the third wire isn't wired to anything, it's just there to physically keep the pot from moving on the table as you spin the little knob!!!!!!!!!!!!!!!!! I'm so annoyed I spent so much time trying to figure out why/where that third wire was going to!!!! Use only two wires for your Chua circuit pots/knobs: the middle one and one on either side.

I had similar issues with my scanning electron microscope build: five pots labeled V1-V5 for variable resistor, and one of them showing connection to: ground, -negative voltage (which in a DC circuit is the same as the ground) and then the incoming wiper wire from ??? Ugh! Anyway, here we go:


PARTS

100 ohm x1

1k ohm x2

220 ohm x4

2.2k ohm x2

22k ohm x2

3.3k ohm x2

TL082 IC Op Amp Chips x2

LEDs x2

On/Off switch x1 (DPDT double pole/double throw 6 contact)

Potentiometers x2

9vDC power supply or two 9v batteries and wires.

Breadboard (or not).

Analog oscilloscope with two probes (or three if you use the "z" input on the back too). Or coax cables with fittings at one end (probably RG-58 BNC-connector 50ohm) to plug into analog scope inputs, and cut off the other ends to hook to the Chua Circuit. Or you could get some BNC female sockets and put them in your Chua's Circuit...but short lengths of coax wire with BNC connectors are super cheap on Amazon and eBay, so I buy them and cut them in half quite a bit: each coax cable cut in have gives me: two BNC to bare-wire cables. BNC plugs into oscilloscope or function generator or Geiger counter, etc. and the other end I solder to whatever circuit I'm building. Some of them were 75ohm, and some were even old 1970s cable TV wires that weren't marked. Whatever. 

Bits of wire, wire strippers, solder and iron if you're going to not use breadboard.

Two 1M resistors only if hooking up to digital oscilloscope or computer. Old analog oscilloscope don’t need them.

Just hook old analog oscilloscope probes to Capacitor 1 and Capacitor 2 (the two near each other) and then ground the probe ground clips to -9vDC (black) on the side rail of the breadboard.

This will be my first ever breadboard project, so I’ll be following Valentin Siderskiy’s instructions pretty much step-by step, but adding my own clarifying notes. Such as: you can leave a wire off of each potentiometer, they only need two in this circuit! Or the ever popular "I think LEDs are polarized so you have to stick them in the right way or they won't light up."

Also, you could easily (I think) leave off: 

On/off switch; 
Two LEDs; 
Resistors for the LEDs; 
Two more resistors that just smooth down the 5k pots to 2.5k--but then you'd need to probably buy actual 2.5k pots. Dumbing down 5k or 10k pots to only 2.5k makes it easier to make slight adjustments to the circuit while turning the knobs. 


Since this is my first breadboard I'm going to leave all that stuff in--when I point-to-point wire it up I'll be able to actually tell how to leave them off without breaking connections. I still think in "point-to-point" and not breadboard or circuit board layouts.

Running the circuit
I used a couple different oscilloscopes. One had 3 inputs: channel a and b (verticals) and a horizontal channel. I just used a and b and set the dial for A vs B to plot the voltages against eachother to get the single scroll chaotic attractor. This gave the same results as my older oscilloscope with a single vertical and single horizontal input (x vs y).

The slightest turn of the potentiometers resulted in HUGE changes to the image on the oscilloscope. This is called bifurcation. 

One of my potentiometers measured only 1.3k instead of 10k when tested on a multimeter: so I replaced it and immediately got better results. I'll probably invest in two full sized pots with convenient knobs to twist.

I had two old mismatched batteries, I'll add new ones.

When I unhook the oscillscope ground clips from the ground wire the whole circuit becomes very sensitive to hand movements. 
Bifurcation was observed: tiny, smooth changes to a paremeter (knob twist) results in huge changes to the output (dot turned into a chaotic attractor). Hysterisis (like my previous post about neon lamp bulbs) was observed: the spot where the chaotic attractor turns on is different from where it turns off--plus there's two knobs that influence eachother. 

Unplugging the inside leg of the 10nf capacitor gave an extremely small, single trace of the famous double scroll attractor. It was very low resolution: it looked like a number "8" written in Old English font! 

Here are some attractors that resulted when I changed one, then both of the pots from 10k to 5k:

Here are some sweet toroidal Class 1 Eigenvalue = 10 (sort of) attractors.

Here are some results after putting in two 5k pots, then replacing one of the batteries with a 9vDC power supply...but varying the DC voltages from around 1.3vDC to 10vDC:

Here is the shape you see right before the classic double scroll: I was playing with the voltage (I replaced one of the 9v batteries with a DC bench power supply and going from 1.3vDC to 10vDC. One of the IC chips was getting pretty warm though):

It's a homoclinic bifurcation, the periodic orbit grew units it collided with the saddle point.







Multiscroll attractor:

You can see how this double-double scroll attractor developed from multiple loops:

The Logusz Attractor (double-double or chaotic quad-attractor as I'm thinking of naming it)...although it's actually pretty close to what others have found as a projection of the Vc2 / IL plane or the Vc / IL1 plane. The literature on this and others:

Anshan, H. [1988] "A Study of the Chaotic Phenomena in Chua's Circuit," Proceedings of 1988 IEEE International Symposium on Circuits and Systems (Cat. No.88CH2458-8). IEEE. vol.1, pp.273-276.

Bartissol, P., Chua, L.O. [1988] "The Double Hook (Nonlinear Chaotic Circuits)," IEEE Transactions on Circuits & Systems, vol.35, no.12, pp.1512-1522.



Anshan in particular backs up what I discovered myself: op-amp voltage adjustments can lead to lots of new patterns and attractors. Of course he found this out in the 1980s--and I'm just playing around in my basement as something to do besides mow my lawn...it's nice to see my "weird" non-perfect, non-double scroll attractors have actual mathematical explanations in eigenvalues (weird math) but also voltages.

Great sources of information that I ripped off:

Professor Leon Chua, the inventor of this chaotic circuit.

"Jim" who made http://www.chaotic-circuits.com/

Valentin Siderskiy, Vikram Kapila and Aatif Mohammed of http://www.chuacircuits.com and published papers and a great Instructable post. Check out "Chua's Circuit for experimenters using readily available parts from a hobby electronics store".

"Chua’s Circuit for High School Students" by Gandhi, Gauruv., Muthuswamy, Bharathwaj2 and Roska, Tamas.

This list of awesomeness; hover your mouse over the titles and you can click and be rewarded with actual PDFs of the articles (and not just crummy citations): http://people.eecs.berkeley.edu/~chua/circuitrefs.html

Easy DIY Mini Tesla Coil (Solid State Slayer Exciter Circuit)

Easy DIY Mini Tesla Coil (Solid State Slayer Exciter Circuit)

Here's a video of it lighting up a light bulb wirelessly in my hand:

The Slayer Exciter is basically a solid state Tesla coil. It’s a high frequency oscillator (or is it actually a type of resonant power supply or an RF oscillator) with a 2N2222a signal switching NPN transistor (or put a PNP in backwards?). 

You do NOT have to manually tune this circuit to a specific resonant frequency. It all just takes care of itself, unlike a regular Tesla Coil. There is a parasitic capacitance to ground as a feedback.

DC to the big (secondary) coil > DC to the Base of transistor, 
DC to the small (primary) coil > to the transistor to ground.

DC goes from the other end of the secondary coil > to the transistor to shut it off.

It does this very quickly at high frequency oscillating (alternating)back and forth…and thus DC current is transformed into AC current.

The Slayer Exciter Tesla coil will function without a top sphere (or torus disc), but the frequency will be much higher.  A lower frequency will reduce heat in your transistor-saving it from blowing up. The Slayer Exciter is sluggish at any rate, which will cause transistors to die as it slowly oscillates on and off…which is why it should have a large heat sink with thermal paste.

You can also double or triple up the transistor: just lay them on top of each other and tie each of the three legs together, but that seems dumb to me: just use a proper heat sink or do what I do and just fun it for less than 30 seconds! I got the TO-18 package version of the 2N2222a transistor which is metal, but round…so the heat sink isn’t as easy to scavenge: it needs to be a star shaped sink with a hole in the center: that’s where you put the transistor.

E= Emitter                  B= Base              C= Collector

Most people build these with an LED (wired backwards), or better yet a Schottky diode (also wired backwards?). The LED acts as a safety device for the transistor, so the transistor doesn’t go too negative voltage. I’m doing without it for now. I like to build things with the least amount of parts as possible. Also, like a gillion people have built these and I'm just having fun here. If it blows transistors, even with a heat sink then I'll add an LED or Schottky diode. It worked first try without heatsink or LED or Schottky diode or even a top collector disc or ball.

Sort of Unnecessary Math: but it lets me know about how many turns my coil has. I see a lot of these with about 100:1 turns, "about" 3 to 5 turns on the primary to "about" 300 turns on the secondary:

                                         Pi = 3.14159

                                                   D = 1.5"

Circumference   =      C = Pi  x  D
                                      C = 4.7"

Feet of wire x 12 = inches of wire.

             197’ x 12 = 2364 inches

2364 / circumference of paper tube   =   # of turns in the coil.

Inches of wire / Circumference = number of turns.

              2364  /    4.7          =   502 turns

The thicker wired "primary" coil of 3 to 5 turns has to be wound around in the opposite direction of the turns of the "secondary" coil!!!!

So I ended up with about 500 turns on primary and 5 turns on the secondary coil.

Building:

-24AWG thin enameled wire (enameled means coated with insulation on the outside); 197 feet. Make sure to scratch away the enameling on the last inch of both ends of this wire!!!!!!!

-Random scrap wire thicker than the 24AWG to make a few (5 turns) of primary coil.

-Paper towel cardboard tube.

-Scotch tape and/or electrical tape to make things easier..

-Stand made out of blue cap from a water bottle to hold tube up (not really necessary).

-2N2222A transitor (metal or plastic, whatever you can order or you can find).

-Heat sink & thermal paste for transistor (I didn't bother since I only run it for about 10 seconds).

-22K resistor.

-Either a 9v battery and connector wires; or about 5v from a DC power supply with wires.

-Knife or sand paper or file to scratch away the last inch of enamel from the thinner wire.

-Metal soup can lid or bottom of soda can cut into dished disc or doorknob or a ball wrapped with aluminum foil for the top collector (I didn't bother with a collector).

-Solder and soldering iron (although you could probably just twist the few components together).

-A small fluorescent light bulb to light up wirelessly in your hand.

You can see the little tab next to the E leg below:

Scrap both ends of thin wire to remove about an inch of enameling. Notice the blue bottled water cap I used as a base:

Red is positive, black is negative from my DC power supply at about 5vDC:

Most "enameled" wire is coated in thin plastic instead of enamal paint or anodizing. That fine. Go with what's cheap:

I use power supplies, not batteries, so I don't need a separate on/off switch. I also left the LED (or Schottky diode) out of this circuit for now. It's just a safety device. If you put an LED in the circuit it will light up when it's "saving" the circuit from going too negative...kinda neat.

So, that's my super simple setup. I gave it around 5vDC and it lighted the light bulb in my hand!

Easy Way to light magic eye tube EM80

Easy Way to light magic eye tube EM80

This is a green glowing EM80 tuning / indicator / magic eye tube. I just wanted to see it glow. I was able to make the glowing green fan shape slowly open and close. They make (made) round ones called "cat's eyes" that wink! These were cheaper to make than moving needle meters, but as you can see from the Geiger counters in old monster movies, needle meters grabbed hold way back in the 1940s. Luckily the failed and demented priciples of socialism in the USSR kept factories producing these tubes in Russia until the 1990s...instead of food or clothing or useful items...they just kept making these tubes that the entire world (including Russia) atopped using in the 1920s! For under $20 including shipping on eBay and Amazon you can still get brand new in box magic eye tubes. 

See the bottom of the page for a video of my capacitance tester that has one.

AC/Furnace and power supply were making a lot of noise in the video. I was also nervous about holding a camera and live wires--so it's loud, weird and shaky.



Here is the stupid simple way I got it to light up, and then open and close:

+250vDC to pin 9
+250vDC to 470k-660k resistor to pin 7

-250vDC to pin 2

5vDC wallwart either output to pin 4
5vDC wallwart either output to pin 5

Touched pin 1 to pin 7 momentarily to work the eye.


When I touched pin 1 to pin 7 the eye closes, but 250vDC power supply sags. I'm only doing it for a few seconds at a time. The grid voltage (g1) on pin 1 is supposed to act to choke off the power to the tube's triode to open/close the eye. It's supposed to be like -1v to -14v, but by connecting the pins I'm hitting it with almost the full -200v I think.

It worked better with a resisitor higher than 220k. Added second 220k to give 440k and it worked but still got too dim when working the eye. A third resistor made it 660k and that seemed better. That's what I uses in the video. I built a decade resistance box which I'll plug in, and then turn dials to easily set different amounts of resistance and see what works better.

My big DC electrophoresis supply was set at only 200vDC in the video: still utterly deadly!

Anyway, the drop in voltage in the power supply is either: supposed to happen (triode shutting down due to control voltage); or it's not a great idea to basically short out your power supply. Most power supplies might pop a fuse/capacitor/blow up, but I was using an electrophoresis supply which is meant to have wires dangling in water/gel for DNA testing...so it might be a little more forgiving.

Here's the schematic:

Here is the replacement of the resistors with my decade resistance box:

I discovered something nobody else online has mentioned: if you use a resistor (or dial up resistance on a box) at 10k you will see a faint ghost image of the open/closed positions on the eye. If you turn the 10, 000 dial right or left you will see these lines move. When you touch pin 1 to pin 7 the lines will be where the eye opens to! Its like a preview! I call these "Logusz Lines".

Here's a photo of my Heathkit DR-1 decade resistance box I bought for a dollar at a resale shop. Heath Inc. used to be nearby in Benton Harbor Michigan.

Extra notes:


All of my posts are just lab notes online. Most are deadly projects! These are not instructions!

Crazy deadly mess of wires. On the left are two of the eventual three resistors in a row. The red wire is +250vDC which splits off: one way goes directly to pin 9. The other goes to 660k resistors which goes to pin 7.

So, what if I put a potentiometer between pin 1 and 7? With it closed it would have to dissipate a lot of power (heat) and possibly melt. I'm not sure if I'd have to ground it (using 3 wires) or not (using 2 wires). Which way would kill me or the circuit?

What if I put a decade resistance box in place of the resistors at pin 7 and dialed it up and down? Power (heat) dissipation wouldn't be a concern, since it wouldn't be connected--only when I touched a wire from pin 1 to 7. This is a great way to dial up a different resistor value without having to solder in/out a bunch of resistors. I had different results with the 3 different values I tried (220k, 440k and 660k). Different amount of eye open/close but also dimming of the entire green output.





Here's the original report: just wires and no resistor so it would glow green:

Here is the pinout for the EM80 tube:

Nothing will happen without a power supply going to the heater pins.
You must add around +200vDC to pins 7 and 9 and -200vDC to pin 2 to get green glow.

To begin:

I needed a 6.3v (AC or DC) supply for heater pins 4 and 5.

I found a wall wart phone charger type thing and cut the end off and attached the bare wires to yellow alligator clip wires. On the wall plug part it had a sticker that said the output was 5 volts DC. Close enough!

I plugged it into the wall and the heater filament inside the vacuum tube gave a tiny orange glow. Success!

Next I needed 250v DC power. This had to be DC.

I was usiing the nifty disposable camera power supply I made for my neon bulb post. But then my 250v DC laboratory electrophoresis power supply ($65) arrived from eBay. So I used that.

As noted in my neon lamp bulb post high DC voltage is very hard to come by: either a camera flash diy conversion, a lucky find on ebay, or splicing wires into a guitar amp or old time tube radio. Lighting up to see the green glow is fine with a camera flash conversion, but I think shorting out to open/close the eye would kill it.

I took a white wire and ran it from the POSITIVE 250v DC output to pins 7 and 9.

Then I ran a green wire from the NEGATIVE -250v DC output to pin 2.

Boom: crazy green glow! So happy.

In the datasheets and magic eye tube tester circuit diagrams the ground symbol actually means the negative DC wire from the DC power supply. A DC power supply only had two output wires: positive and negative. By an annoying convention ground can mean the negative wire of the power supply or battery you're using.

The spec sheets comes right out and says AC or DC is fine for the heater pins, but they don't make clear that the 250v supply needs to be DC.

To get the green "eye" to open and close you can sometimes short certain pins together. To slowly open and close the eye the proper way is to input NEGATIVE -1v to NEGATIVE -14v. I do not yet know if that is AC or DC or if it's relative to the 250v DC? Like: is it -1 volt or 250-1= 249v?

Also pin 1 is the control grid pin. How do you add voltage to a single pin? Some specs seem to show positive and negative wires going towards that single pin. If it's wired in how do you raise and lower the voltage to open and close the eye? Add a potentiometer?

Supposedly, if you ground the control grid the eye will open. Give it negative volts it will close. This is "biasing" the tube.

Without any resistors Connecting pin 9 to pin 1 turns off the green. That makes sense because pin 9 has the full +250vDC and pin 1 (control grid) wants negative DC. It seemed like a bad idea to continue testing this. I won't connect pin 9 to anything anymore. I'll just unplug everything if I want darkness.


Here's more "official" ways to open/close the eye, but I haven't tried them yet, mainly because I don't have an old timey radio with an AVC (auto volume control) to feed into pin 1.

Here is my Sprague capacitance tester that has a round "cat's eye" magic eye tube:

Boffon's Needle

Boffon's Needle

This experiment used integrals to calculate the probability of a needle being dropped on a sheet of paper with lines drawn on it landing on a line. I don't care about that, except that in 1777 The Comte De Buffon (Georges-Louis Leclerc) figured that the probability of a needle landing on a line is two divided by Pi.

So here's what I did: I found a box of needles (pins) that were 3/4" long. Then I drew lines on a piece of paper spaced at 3/4" from each other. This makes the needle and the space both 3/4" and thus they have a scale of "1". 

I dropped 11 needles and got 7 hits.

So:  2 x needle unit 1 x 11 drops divided by 7 hits = 3.14285

2(1)(11)/7 = 3.14285

Pi is = 3.141592...

This was the first (and only) drop I did. By the way, if you take a ruler and continue the lines every 3/4" the 3 needles that fell towards the bottom wouldn't have hit any lines...had I bothered to draw them in. The lowest needle would have been close though.

Let's take that scenario:  2(1)(11)/8 = 2.75

Yeah, I'll fudge a little and keep my nice 7 hits instead of 8.

So, eventually when I post my RF and AF probe builds they'll probably have something about sine waves (which are 2 pi in proportion...I think).

DIY Neon Lamp bulb / Nixie tube power supply

DIY Neon Lamp bulb / Nixie tube power supply

Neon lamp bulbs (the high output ones I have at least, which are C2A-ND) need about 95vAc or 135vDC to ignite. Placing a 30k Ohm resistor keeps the bulb from exploding. Later on, in the oscillation circuits I'm building I'll be using some NE2-A1A bulbs which only need 65AC or 90DC volts to light up ("strike")...I'll be using those with my new Agilent 0-120V DC power supply.

I didn't have a 30k resistor handy, so I just put two 15k ones end-to-end, which totals 30k. You only need 0.25 watt resistors, the huge blue ones I used can handle 2 watts, which is why they are so huge.

When you plug a neon lamp bulb into an AC power source both the cathode and the anode glow.

When you plug a neon lamp bulb into a DC power source only the negative side will glow. Swap wires and the other side will glow.

Getting 95v of AC power is easy: just hook a variac into a wall outlet and ramp up the juice. Some people just plug the neon bulb (with a resistor soldered to one leg) directly into a wall outlet, but that's dangerous because itsi easy to touch or cross the legs.

Finding a 135v DC source is pretty hard-unless you make your own.

I took a disposable film camera with flash and took the circuit out of it. This is very dangerous because there is a HUGE capacitor inside which can kill!  

Before I took apart the camera I fired the flash, then I removed the battery, then advanced the film ratchet inside the camera forward to recock the shutter and fired the flash. This helped to bring the voltage in the capacitor down from its 350v level.

Once the camera was open I removed the circuit board without touching the components because they could still shock! Luckily with I put a voltmeter on the two wires coming out of the capacitor it read 30 volts, here is where I put a large resistor across to bleed away the rest of the voltage-sometimes I put the blade of an insulated handle screwdriver to discharge a capacitor-but that makes a loud bang and huge spark and can actually blast away some of the screwdriver metal!

Once the capacitor was reading only 5 volts I put a screwdriver blade across both it's wires and nothing happened: safe!

Then I cut out the capacitor (two snips) and then attached a wire to each spot that they connected to the board: those wires then when to my neon bulb (and resistor) legs.

At this point I put the battery back in a used a pair of insulated pliers to hold the circuit while I used an insulated screwdriver to depress the "on" button on the circuit board: success! 

My cheap voltmeter couldn't measure the high frequency voltage going to the output wires. The readings just bounced all around, but the high output neon bulb lighted right up.

After removing the battery the board is still dangerous: even though the huge death capacitor is gone there is still at least one more capacitor on the board that holds enough energy in it to give a nasty shock! For safety I'm going to put this whole thing in an insulated container; once I figure out a way to either press the on button from outside without getting shocked, or solder a wire to across the on switch to make it permanently on.

Since I have a bunch of low voltage DC supplies I soldered a wire to each of the AA battery holder. I'll run these wires to a 1.25vDC power supply to power this setup. That'll save on batteries. That will give me a power supply that gets 1.5vDC input but outputs 135vDC+.

Next, for fun I cut out the actual xenon flashtube. It didn't hurt the circuit and I hooked it up to my 5000v transformer and variac: at about 1000v there was a purple thunderstorm looking action in the bulb: many jagged strings of lavender lightning in the little tube.

Of course AC power is better for Neon Lamp Bulbs: both filaments (actually electrodes) are glowing, the voltage is lower and alternating at 60hz so the "wear and tear" on the filaments is spread out. When only one electrode is glowing because of DC power it is: turned "on" 100% of the time (not alternating) and all the (higher) voltage is sent to a single electrode. This is why neon lamp bulbs last about 50-60% longer when fed by AC power.

Neon Bulbs and Root Mean Square AC Voltage

120v AC house current fluctuates between -170v and +170v. So why don’t we say that the AC house current is 170v? Because if you average 170v AC you get zero!

   -170 + +170 = 0  0/2 gives you an average of 0v. So a meter that reads an "average" voltage would always show the wall outlets in your house as having "0v", which would be mathematically correct, but obviously weird!

What if the meter showed you exactly the voltage? Your meter would show -170, -169, -168...+168, +169, +170 volts; all cycling 60 times per second up and down, so your meter would be a blur of numbers on the screen.

So, instead of taking an average voltage, even cheap multimeters are designed to take the: 

Root Mean Square (RMS) of the AC voltage

+170 squared = 28900     

-170 squared = 28900

The square root  of 28900 = 1.414

170 divided by 1.414 = roughly 120.

The average AC output of a light socket in your home is 0v.

The root mean square of a light socket in your home is 120v.

The "120v" number is more useful and less deadly than the "0V" number would be. Think about it: let's say you have an AC current that was 2 million volts, that would be +2M and -2M which would still average out to be "0v". This is why you sometimes need to plug "170v" into an equation instead of 120v so you don't blow up your circuit.

So, what does this have to do with neon lamp bulbs?

Well, my particular model of neon lamp bulbs need 95v to light. So my bulbs (on AC power) only are lighting at +95v to +170v and -95v to -170v.

The red areas are when the light bulb is on. So, the lamp is only working about 44% of the time. This works out to close to the 50-60% longer useful life when running on AC.

When a high brightness version of a neon lamp ages it: sputters (sprays) metal from the filaments, which darkness the glass until it turns black. This process is constantly going on. I suppose if you had a neon lamp running on DC only one electrode would be sputtering--so once half the bulb's glass was blackened you could just switch the legs of the neon and that would turn on the other electrode, giving you a longer time. However, the electrodes also end up needing higher and higher voltages to light--once a neon bulb running on AC needs about 160v to ignite the bulb's useful life is over because that's too high to reliably ignite. In the meantime the bulb would have: started flickering instead of showing a steady light; and it would have significant blackening from the vaporized electrode metal inside the bulb.

Neon bulbs need ionization already occurring in the neon gas to be able to start. There are two methods in use: one is to put a little bit of radioactive material into the bulb (an isotope of Krypton); or having the bulb exposed to room light! Yep, neon bulbs can't light up in a completely darkened room (or at least not very easily). That is why new bulbs sometimes flicker in a dark room, but if you shine a flashlight on them--or just flick on the room's light to get some regular old light photons ionizing the neon in the bulb. This is called the dark effect.

There are a ton of different things you can use neon bulbs for: oscillators, tone oscillators to make electric organ sounds, instrumentation lights in rugged environments that would cause an LED to fail, a bistable flip-flop circuit for use in very basic computers as and/or/majority gates, ring counters, a sort of radiation sensor very similar to a geiger counter using the lamp's photosensitive (dark effect) properties, triggering and pulsing other circuits, delay circuits, an Is it AC or DC? meter, voltmeter which lights corresponding to various voltage ranges, etc.

You can duct-tape them to a stick and point them near equipment to see if there is RF or high voltage--you can even hold the bulbs near spark plug wires in your car to see if each plug is actually firing! Because it lights up under outside influences (static, ionization, RF, high voltage fields, etc.) you can use it as a touch control of sorts too.

At this point I'm just happy my little neon lamp (and 30k resistor) spurred me on to: make a DC power supply; light one or the other electrode via DC; and lighting both electrode via AC.

Here is a video of the xenon flash hooked up to my 5000v transformer. Like bolts of lightening in a jar.

Neon Oscillation Circuit

Here are two schematics, well one is more of a drawing and one is a circuit layout. They go with the photo: 3 blinking neon bulbs.

This circuit is super easy to build. The parts were:

3 ne-2/a1a neon bulbs

3 1uF ceramic capacitors

3 1M resistors

Not needed but for fun: piezoelectric buzzers.

The blobs of solder were from rearranging things to see what would happen. For that purpose I started crimping the ends of the ceramic capicitors so I could add or subtract them to the circuit without soldering:

Also shown is a piezoelectric buzzer. I used it in place of a capacitor as an experiment. Here are some results:

No capacitors or piezo: the lights turn on and the brightness varies a little as voltage varies.

1 piezoelectric between two of the bulbs: all 3 bulbs blinked quickly. They blinked faster with more voltage.

1 piezoelectric and 1 cap: the bulb with the piezoelectric blinked quickly and the other two bulbs alternated slow blinks. More voltage sped all blinks.

1 piezoelectric and 2 capacitors: two bulbs quickly blinked alternatively and third gave a longer blink (longer time bulb was lighted).

2 capacitors: quick blinks from bulb with no cap, bulbs with cap had longer blinks. No cap bulb blinked more than each capped bulb.

3 capacitors: bulbs blinked at different times. Higher voltage only slightly sped up the blinks.

At no time did the piezoelectric buzzer make a noise, probably a change in resistor values might be needed. Possibly a cap used with a piezoelectric would have made noise.

So what is happening?  The capacitor charges up. Due to hysterisis the neon bulb doesn't conduct until the capacitor reaches the bulb's striking (trigger) voltage. Only then will the bulb conduct which lights the bulb and discharges the capacitor. When the capacitor voltage drops, the bulb stops conducting and the capacitor begins charging starting the whole thing all over again. The circuit charges, fires, then relaxes. It's a relaxation oscillator.

Well, more specifically: with just 1 bulb, cap and resistor using DC power this gives out a sawtooth wave. It would be a Pearson-Anson Relaxation Oscillator.