What's better than a single LED? Lots of LEDs! A fun way to make a small linear display is to use two 12-bar Bi-color bar graphs. However, this LED bar graph is 'multiplexed' - so to control all
48 LEDs you need a lot of pins. There are driver chips like the MAX7219 that can help control a bar graph/matrix for you but there's a lot of wiring to set up and they take up a ton of space. Here at Adafruit, we feel your pain! After all, wouldn't it be awesome if you could control a colourful bar graph without tons of wiring? That's where this adorable LED bar-graph backpack comes in. Much like our 8x8 and 7-segment backpacks, this backpack pairs perfectly with our bar graphs and manages all the LED control and multiplexing.
The backpack uses a driver chip that does all the heavy lifting for you: It has a built-in clock so it can multiplex the display. It uses constant-current drivers for ultra-bright, consistent color, and 1/16 step display dimming, all via a simple I2C interface. The backpack comes with address-selection jumpers so you can connect up to eight of these bar-graphs on a single I2C bus. You can also mix and match the bar-graph breakout with our other types of I2C LED backpacks.
The product kit comes with:
A fully tested and assembled LED backpack stick
Two 12-bar bi-colour bar-graphs
4-pin header
A bit of soldering is required to attach the matrix onto the backpack but it's very easy to do and only takes about 5 minutes.
Of course, in classic Adafruit fashion, we also have a detailed tutorial showing you how to solder, wire and control the display. We even wrote a very nice library for the backpacks so you can get running in under half an hour, displaying images on the matrix or numbers on the 7-segment. If you've been eyeing matrix displays but hesitated because of the complexity, this is the solution you've been looking for!
Note: Arduino board, cables and breadboard are NOT included
Revision History
As of August 19th, 2024 – We've updated this PCB to have Stemma QT connectors on the I2C lines for plug-and-play usage. We've also updated it with Adafruit Pinguin to make a lovely and legible silkscreen.
I needed 12 LED bargraph for a Ghostbusters trap model, but the simplicity in sorting the multiplexing with the backpack made it worth nabbing this.
Very simple to put together, I actually soldered a ribbon cable to mount my bargraph remotely, and hooked a single red LED into the unused second slot so I could run all my LED's in the model through the backpack. No need to add resistors, very simple wiring back to the arduino. Simple to get working in code, looks great and nice to have the 3 colours which makes the trap a bit more interesting than most (if not movie accurate when running multi-colour).