Making Android Accessories with IOIO

Chapter 4. LED Matrix Light Show

This chapter uses a multicolor LED matrix to make a fun charger for your Android phone (Figure 4-1). In this particular case, “fun” takes the form of a marching Space Invader animation—and if that isn’t fun, I don’t know what is!

Figure 4-1. LED matrix light show

The project has a variety of different modes: it can just display a static image, or it can display an animation, or it can make use of the phone’s microphone to provide a spectrum type display. If you start your music player on the phone before you start the IOIO Matrix app, it will respond to the sounds coming from your phone.

This is the only project in the book that will not work using a Bluetooth adaptor rather than a USB cable. This is because Bluetooth simply isn’t fast enough to send the commands to the pins to refresh the display.

The Design

In this design, the IOIO board uses 24 of its pins to control the LED Matrix. It requires 24 pins because the LED Matrix is arranged as a grid of LEDs. Each cell in the matrix actually has two LEDs in it, one red and one green. This is used to set the color of any individual cell to red, green or—if both LEDs are lit at the same time—orange.

Schematic

Figure 4-2 shows the schematic diagram for the project.

Figure 4-2. Schematic diagram for the project