What could be better than one LED? Lots of LEDs! A fun way to make a small screen is to use an 8x8 matrix or a 4 digit 7 segment display. Matrixes like these are multiplexed' - so to control all seven-segment LEDs, you need 14 pins. This is a lot of pins, and there are driver chips that can control a matrix for you, but there is a lot of wiring to install and they take up a lot of space.  After all, wouldn't it be great if you could control a matrix without tons of wiring? That's where these adorable LED matrix backpacks come in.

The matrices use a driver chip that does everything for you: they have a built-in clock to multiplex the display. They use constant current drivers for ultra-bright and constant colors (the images above are photographed at the darkest setting to avoid overloading our camera!), dimming of the 1/16 step display, all via a simple I2C interface. The backpacks come with address selection jumpers so you can connect up to four mini 8x8 or eight 7-segments (or a combination, like four mini 8x8 and four 7-segments, etc.) on a single I2C bus.

The product kit comes with:

    A fully tested and assembled LED backpack.
    Ultra-bright red display with 4 digits 0.56" high and seven segments.
    4-pin connector

Some welding is required to attach the matrix to the backpack, but it is very easy to do and takes only about 5 minutes.

Features

This card/chip uses the 7-bit I2C address between 0x70-0x77, selectable with jumpers.

    Backpack dimensions: 27mm x 50mm x 4mm / 1.1" x 2" x 0.16" x 0.16".
    Backpack weight : 5.3g
    Screen dimensions 7 segments: 19mm x 50mm x 14mm / 0.75" x 2" x 0.56" x 0.56".
    Display 7 segments Weight : 8.4g

Documentation

Adafruit LED Backpacks