## Introduction: 9-Charlieplexor (9-pins for 72 LEDs)

This Instructable shows how to wire a 9-Charlieplexor. (Formally this is a "Charlieplexing circuit with 9 nodes" capable of controlling 72 LEDs or less.) A general method could be taken from this layout for larger Charlieplexors. I will likely put in a larger Charlieplexor circuit that I might get made, but I stopped at a setup large enough for an 8x8 array. This is because wiring a 9-CP by hand in a non-compressed array already involves over a hundred circuit connections, not to mention the 72 jumper and 72 lead connections to the LEDs themselves. I have already built the LED arrays (in 3 panels) and I plan to have a ribbon coming off each sub-array panel to plug into the board above. The 72 jumpers are pretty quick to wire, but it is already obvious that ~24 wires coming off each panel would be painful to plug in individually.

The reason I'm building this is to control an LED game that I want to build into the walls of the cardboard barn I built for my daughter. I wanted a board that I can just plug in the LED leads and not have a formal array (like an 8x8 or similar, though this board can certainly be used to do that).

There are many Charlieplexing solutions out there, but I was surprised at how hard it is to find a how-to-wire example for a "flat" breadboard circuit driving more than 12 LEDs. Many LED cubes are chip driven solutions. I felt like I understood Charlieplexing, and I didn't want to spend a few days reading up on the chips from Maxim Integrated (which appear to have transistor powered drivers, etc.), so I built my own wire-only/breadboard solution.

The idea came about while looking at 3 pin Charlieplexing circuits like the one on Instructables.com. Looking at the circuit it occurred to me that Charlieplexing is kind of like chemistry, where instead of a bond with paired electrons each node is basically connected by a edge consisting of two paired diodes (see drawing). With that simplification I found myself looking at Network Theory which led me to Graph Theory and Complete Graphs, which are basically drawings of Charlieplexing systems using the one-line-equals-two-diodes idea, and the nodes are the number of pins.

So instead of building a 9-dimensional octahedron (with center node, which I'd still like to do...), I realized that I just needed a list of addresses that correspond to each node touching every other node, without duplicates.

With the ideas above and some spacing for wire management (using Numbers/Excel then iCircuit), I came up with the circuit shown.

Let's build it!

## Step 1: Materials

I didn't want to strip a bunch of wires, so I used a set of colorful breadboard wires to make the "front" or horizontal connections. I used insulation on one side of the board (front, and it looks better) and then "rails" hidden on the back of the board.

Materials:

1. 5cmX7cm high quality breadboard (18 x 24 through holes)
2. Insulated wire
1. I used a box of pre-measured wires (basically a solder-less breadboard kit)
2. I stripped long pieces from the box set for rails so all my interconnects were of the same material
3. Uninsulated wire or stripped wire
4. Your preferred connection setup for 72 LED wires and 9 Arduino connections. I used:
1. 2x36 male pins for LED jumpers: 2x8 pin sets (4) and a 2x4 pin set (1)
2. 1x9 female socket
5. Soldering iron, solder, "scrub pad", etc.
6. Ohm meter (or DMM/Digital Multi-Meter, something to check the connections)
7. Flush-cut wire snips
8. Wire stripper
1. I stripped the same wire for the rails
2. And I still had to strip some pieces when I ran out of one size

Recommended:

1. Permanent felt-tip marker for marking board (and marking wires if you're going to strip them yourself)
2. Circuit board holder (I finally went and got one, totally worth it)
3. Desk lamp (my eyes aren't what they used to be)
4. Isopropyl alcohol (rubbing alcohol) for cleaning off flux and stray marks
5. Tissues and compressed air for cleaning (a cotton swab might have worked better)

## Step 2: Wire the Horizontal Connections

First I drew in where I planned to put the components with a fine tip permanent marker.

Using good soldering methods (as best I could) I inserted and bent the insulated wires to hold them in place while soldering (as much as possible).

As I completed each "Index" or wires for a block of pins, I put in the actual pins and held each block in place by soldering in two corners. Then I trimmed the wires, folded them down and made all the connections.

This circuit was made to fit on an 18x24 hole board, so I made a few jumps to reduce the number of rows.

I made the simple connections first and saved the jumper connections for last to keep the layout as clean as possible. The last horizontal connections were the bottom jumpers to Indexes 3 and 5, and finally the jumper for Index 9 across the board. Pretty much anything that wasn't easy to draw in the circuit was wired at the end of a section (see the jumpers listed after the rails in the next step).

The last two pictures show the horizontal connections to this point.

## Step 3: Input Block and Input Rails

The "rails" are the vertical wires carrying the current for pins 1-7. I configured the board so that pin 8 and pin 9 would be short or single jumps, allowing me to further compress the board.

I ended up trimming all the extra wire before laying the rails. I had intended to lay the rail beside the horizontal wire "tails" but I ended up trimming the tails and laying the rail on top of the trimmed connections.

1. First I soldered in the edges of the 1x9 female block to hold it in place (same side as the male pins)
2. Then I found it better to remove all the excess wire to make room for the rails on the back.
3. Then I took my stripped wire and first connected the tip to one of the pins of the female block
4. Then I connected the bottom-most connection and trimmed the rail
5. This held the wire somewhat in place as I worked my way down the rail making connections
6. Occasionally I used the tip of a pair of pliers to hold down the (hot!) wire wile making a connection
7. I completed rails 7 through 1 and then went back and wired pin 8 connections
8. Then I wired pin 9 jumper and connection
9. Finally, I made the compressed connections:
1. jumper 2 from 8.2 to 2.1
2. jumper 4 from 5.4 to 4.1

## Step 4: Cleaning and Marking and Sub-9 Addresses

Finally I cleaned the board with isopropyl alcohol to remove flux and component markings.

Then I went back and labeled the Indexes to simplify connections later.

The numbering system is as follows, with each 8-block corresponding to 16 LEDs.

As you may know, pin pair 2.1, for example, actually controls the LED oriented 2-1 and LED oriented 1-2.

(Counting down seemed to set up the numbering better for sub-9 Charlieplexing.

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For a 9-Pin Charlieplexor the pin addresses in groups of 8 are:

9.8, 9.7, 9.6, 9.5, 9.4, 9.3, 9.2, 9.1

8.7, 8.6, 8.5, 8.4, 8.3, 8.2, 8.1, 2.1

7.6, 7.5, 7.4, 7.3, 7.2, 7.1, 3.2, 3.1

6.5, 6.4, 6.3, 6.2, 6.1, 4.3, 4.2, 4.1 *

5.4, 5.3, 5.2, 5.1 **

*this would control an 8x8 array

**with 9x8 you can control 72 LEDs, these are the "leftover" pins for 8 more LEDs (beyond 64)

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For the 3-Pin Charlieplexor shown at the beginning, the pin addresses are simply the 3 and 2 Indexes:

3.2, 3.1

2.1

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And an intermediate example, say a 5-Pin Charlieplexor (drawn in 3D on first page) the pin addresses would be:

5.4, 5.3, 5.2, 5.1

4.3, 4.2, 4.1

3.2, 3.1

2.1

-

Enjoy!

## Step 5: Next Steps

For me, the next steps will be:

1. Become more familiar with the basic Arduino code for Charlieplexing
2. Set up the 3 pin example using this board for testing.
3. Expand the example code(s) to control 72 LEDs
4. Build the "array" or layout of LEDs I want in the cardboard barn
5. Confirm that it works and that my daughter can't eat the LEDs or get to the wires (I have a plan)
6. Add in switches and Arduino code to make games like "chase the light" or "pick your color"
7. Add LEDs inside the switches and in the ceiling (this will be a second or third small array with different colors)

Addendum - Right after I posted this Instructable, I saw manu4371's post for arduino attiny85 charlieplexing. Be sure to check out his/her awesome animated graphics!