Chaos Circuit
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This Instructable shows you how to build a chaotic circuit using parts from RadioShack, a widespread hobby electronics store in the USA. The only part RadioShack does not provide is an oscilloscope, but those are expensive anyway. Hence, we'll also show how you can use a USB Audio Adapter or a Desktop soundcard as an oscilloscope (or as we call it, the Poorman's scope).

It allows you to build a Chua's circuit with parts locally accessible in a short period of time without dealing with online shipping.

Chua's circuits are some of the simplest kinds of chaotic circuits. They are considered to be a classic example of true chaos due to their design and output. Using an oscilloscope you can witness a Chua's circuit create the strange attractor known as the double scroll. These beautiful patterns are truly chaotic and can be modeled by relatively simple nonlinear equations.
On top of being a great example of chaos, they are easy to build. These circuits, invented by Leon Chua, also have many real-world uses ranging from research, to music and encryption. In fact, customized circuits can be implemented almost anywhere where real chaos or nonlinear output is necessary.

You'll be able to have a chaotic attractor in the palm of your hands in just one day, be it for a hackathon, class demonstration, research, or personal curiosity.

Step 1: Go Shopping

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RadioShack stores differ from location to location. Some are entirely focused on consumer electronics and have very few items for hobbyists. Know which RadioShacks in your neighborhood actually have component drawers in the back. (Here in Downtown Brooklyn, 457 Fulton Street - Bad, Court St - Good, Atlantic Ave - Better).

Even if your RadioShack does have drawers in the back be prepared to improvise or visit a couple of places. Below are tables, parts, and other equipment-all available at RadioShack-that will allow you to put together and view the output of your Chuaís circuit without fancy equipment.

Basics Components*

# Description Store SKU Qty. 1 Duracell 9-Volt Battery Two Pack * N/A 1 2 9V Snap Connectors (5 PCK)
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270-324, 270-325 1 3 Linear-Taper Potentiometer (10k or 5k)
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271-1715, 271-1714 2 4 Resistors (500-Piece Value Pack)
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271-003 1 5 TL082 (8-PIN DIP)
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TL082/TL082CP 4 (2 + 2 extra) 6 0.01uF 10% Film Capacitor
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272-1065, 272-1051 1 7 0.1uF 10% Film Capacitor
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272-1069, 272-1053 1 8 DPDT Toggle Switch
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275-666 or any other DPDT switch 1 9 20 Assorted LEDs
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276-1622** 1

Note*: If you want the raw BOM (Bill-of-Materials) instead of a RadioShack shopping list click here.

Note**: It is my personal recommendation to use brand name 9V batteries such as Duracell. RadioShack has itís own brand of batteries that gave me trouble in the past.

Note***: We only need two LEDs for this project. They come in two per package under the following SKUs: 276-021, 276-209, 276-022. I recommend the 20 pack because it's a bargain in comparison and the LEDs will fry if you hook them up wrong, hence having extras is always good.

Tools and Materials

# Description Store SKU Qty. i Hookup Wire (22AWG Solid)
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278-1221 1 ii Solderless Breadboard Jumper Wire Kit
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276--173 1 iii Breadboard
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276WBU202 or any other breadboard 1 iv Wire Stripper/Cutter
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6400223, 6400224*, 6400225 1 v Mini Long-nose Pliers
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6400062 1 vi -5-Piece Basic Soldering Set**
(not in figure)
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64--2802 1 vii -Rosin Core Solder (2.5 Oz.)
(not in figure)
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64--005 1

Note*: Best option.

Note**: This project does not require any precision soldering. The simplest/cheapest iron will suffice. Iíll be using my Weller WESD51 Digital Soldering Station.

Oscilloscope/Poorman's Scope

To see the chaotic attractor you need an oscilloscope, and we can make a cheap one with these parts...

# Description Store SKU Qty. A 3 Ft. Stereo Patch Cable, Dual-RCA Plugs to Dual-RCA Plugs
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RCA* 1 B 14" (35.3CM) Insulated Test/Jumper Leads
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278-1156 1 C BEHRINGER U-CONTROL UCA222 ** UCA222 1 C 1 Mega-ohm Resistor
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271-1356
*** 1

Note*: You can get the same RCA cables at your local dollar store as well.

Note**: You can get a UCA222 online, however any USB Audio Adapters that has a stereo input will work. Some are sold in music instrument stores such as Sam Ash.

Note***:This resistor is actually in the bag of 500 resistors listed in the first table

Step 2: Create Breadboard Switch

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RadioShack does not have any DPDT (double-pole, double-through) switches that can fit into a breadboard. We'll use panel-mount DPDT switches and solder 22AWG wires to them instead.

  • Cut 3 pieces of 1.5" (4cm) red 22AWG wire.
  • Cut 3 pieces of 1.5" (4cm) black 22AWG wire.
  • Use the wire stripper to strip the tips, and hook the wires to the DPDT switch connectors as shown in the images above. One side is for +9V (red), and the other for -9V (black). Use the pliers to help.
  • Solder the wires to the switch connectors as shown in Figures 3 and 4.
  • Use the wire stripper to strip the ends of the wires to have about 8mm (1/4") exposed. (See Figure 5)

  • Plug the switch into the breadboard. Do all the connectors reach into the board? Can you flip the switch without it falling out? (See Figure 1)

    You may realize that it is not necessary to solder on all six connectors for the circuit to work, but I strongly recommend doing so for structural integrity.

    Step 3: Assemble -9V GND 9V Source

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    Here you will put together the circuit that connects the 9V batteries to the rest of the board. We use LEDs to help indicate that the batteries are working and to remind us to turn the switch off when you're done.

    Note that you need to use the 220 ohm resistors in series with the LEDs, or else too much current will flow through them and they will burn out.

    Follow the the images above which provide a breadboard layout, schematics and pictures of the actual board. Use whichever image your most comfortable with to build the circuit.

    Make sure to test that BOTH LEDs turn on. Note that LEDs won't work if you plug them in backwards.

    Step 4: Solder Potentiometers

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    RadioShack does have 10k potentiometers that you can fit inside a breadboard. We don't use them because it's too hard to tune the chaotic circuit into a chaotic mode with such small potentiometers. We'll use these big ones primarily for dexterity.

    Solder long wires on all three leads for both potentiometers. We will only use two leads, but use the third one for structural integrity. We will want the potentiometers to be as steady as possible when we tune them.

    Step 5: Assemble Chaotic Circuit

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    Now it's time for the bulk of the work. Build the chaotic circuit.

    1. Prepare all the components that you need before building the circuit as I did on the white paper in the image above.

    To help you find them, here are the resistor values you will need with their color code:

    100 ohm x1 R7 Brown Black Brown Gold

    1k ohm x2 R8, R9 Brown Black Red Gold

    220 ohm x2 R1, R2 Red Red Brown Gold

    2.2k ohm x2 R3,R11 Red Red Red Gold

    22k ohm x2 R4,R5 Red Red Orange Gold

    3.3k ohm x2 R6,R12 Orange Orange Red Gold

    2. Turn the Switch OFF, make sure the LEDs are not on. Don't build the circuit while the power is connected.

    3. Start building the circuit, in the images above your are provided the breadboard layout, schematic and photographs of the circuit.

    4. Check that you built the circuit correctly

    5. Check that you built the circuit correctly

    6. Check that you built the circuit correctly

    7. Turn the switch ON.

    Check that the LEDs go on as they should.

    Feel if the 9V batteries are not too hot.

    Feel that the ICs are not too hot.

    If the batteries or the IC is hot, you will probably need to replace them.

    Next part is to view the chaotic attractor on the screen. If you have an oscilloscope skip to Step 7.

    Step 6: Poorman's Scope

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    If you have an oscilloscope skip this step.

    The Poorman's Scope is a great replacement for an oscilloscope in many situations. The bulk of the work in this step is to make probes that will fit into the RCA slots of the USB Sound Adapter.

    The software we use to see the chaotic attractor is called Soundcard Oscilloscope and the latest version can be found here.

    1. Grab an RCA cable and snip off the tip of one end.

    2. Look inside. As you can see there is a conductive wire in the center, and conductive wire along a circle around it.

    The inner conductive wire holds the signal, and the outer is ground. We will access both.

    3. Cut the outer casing about 1/2" (1.27cm) along the wire, but not deep. Just deep enough for you to bend the outer casing off. Get the ground conductive strands out of the way, and cut again to get to the strands at the inner core. NOT TOO DEEP, you don't want to cut the strands.

    4. Go down another 1/2" (1.27cm) and this time only remove the outer casing. You should now have access to both the inner and outer strands. Make sure they don't touch! Cut the ground strands short enough that they won't touch the bottom of the signal strands.

    5. Do this again for the other RCA cable.

    6. Connect the green alligator clips to the ground strand. Green is ground by convention!

    7. Connect the RCA plug into the INPUT of the USB Soundcard Adapter.

    And you're done! You just made a Poorman's Scope.

    Making the probe can take a bit of practice. You can get the same RCA cables at a dollar store, and keep cutting till you get it right.

    Step 7: Enjoy Chaos

    Chaos Circuit

    The videos below explain how to view the circuit output, either in a standard Oscilloscope, or with the Poorman Scope from the previous step.

    Oscilloscope:

    Connect the circuit to the oscilloscope. If you have a real oscilloscope, just connect the probes to capacitors C1 and C2.

    Poorman's Scope:

    If your using a Poorman's Scope, connect to C1 and C2 using the alligator clips with a 1Mega ohm resistor in between.

    1Mohm resistors are: Brown Black Green Gold

    Tune the potentiometers slowly.

    Enjoy!

    For more details on Chua's circuits in general check out www.chuacircuits.com

    Valentin Siderskiy and Richard Kroon

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