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Many people, inspired by KeyChainino’s Charlieplexing, have developed their own device using KeyChainino’s sketch from my github.

Someone has designed it’s own matrix schematic, someone else asked to me for the KeyChainino’s schematic to help them in their KeyChainino replica.

KeyChainino was born to help people understand how charlieplexing works and to fit in a pocket – just in a keychain – So, if you want to build your own KeyChainino, continue reading this post!

Some post ago, I’ve explained how to use Charlieplexing with Arduino to drive many LEDs, with only few pins.

Today I want to explain you how to build your Charlieplexing matrix in easy way.

First you need to know the numbers of columns and rows you want to use in the matrix.

If you want to build the same matrix of KeyChainino, you have 6 COL and 5 ROW.

How to design the LEDs and pins connections?

Simple, first create a table and put the pins you want to use both in the X and Y axis. In the X axis we have the anode pins, in the Y axis we have the cathode pins.

Surely you understand that we can’t connect an LED between the same pin. So we need to delete the impossible connections, and, to connect 6 COLs of LEDs, we must use 7 pins – from 0 to 6.

Now, we can add the LEDs in the table in this way:

We stop when we reached our desired numbers of LEDs. So don’t use the pins 5 and 6 in the ROW, but we use them in the COL. We can update our table in this way:

Now, every LEDs has its right connection between two pins, one for anode and one for cathode.

You can choose different pins and different pins order in the table, but you have to change it both in column and row.

In KeyChainino I used these pins:

To make the real matrix connection for the LEDs, you can follow the table diagram:

Connect LED1’s anode to the pin 1 and its cathode to the pin 0.

Connect LED2’s anode to the pin 2 and its cathode to the pin 0. And so on.

Here the KeyChainino schematic to understand how connection works.

Now, as explained in the previous post, you can create the LEDs connection in the Sketch.

Anyway you can look up every KeyChainino Sketches to figure out how handle the Charlieplexing matrix.

Now you have all the elements to build you own KeyChainino.

Otherwise, if you want a ready to use KeyChainino, that fits in a keychain, you can buy it here!