When you buy a pack from Adafruit, it comes with the fully tested and assembled backpack as well as a 7-segment display in one of the colors we provide (say, red, yellow, blue or green). You'll need to solder the matrix onto the backpack but it's an easy task.
Remove the parts from packaging and place the LED matrix OVER the silkscreen side. DO NOT PUT THE DISPLAY ON UPSIDE DOWN OR IT WONT WORK!! Check the image below to make sure the 'decimal point' dots are on the bottom, matching the silkscreen.
Turn the backpack over so it is sitting flat on the matrix.
Solder all 14 pins.
Clip the long pins.
Now you're ready to wire it up to a microcontroller. We'll assume you want to use a 4pin header. You can also of course solder wires directly. Place a 4-pin piece of header with the LONG pins down into the breadboard.
Place the soldered backpack on top of the header and Solder 'em!
We wrote a basic library to help you work with the 7-segment backpack. The library is written for the Arduino and will work with any Arduino as it just uses the I2C pins. The code is very portable and can be easily adapted to any I2C-capable micro.
Wiring to the matrix is really easy
- Connect CLK to the I2C clock - on Arduino UNO thats Analog #5, on the Leonardo it's Digital #3, on the Mega it's digital #21
- Connect DAT to the I2C data - on Arduino UNO thats Analog #4, on the Leonardo it's Digital #2, on the Mega it's digital #20
- Connect GND to common ground
- Connect VCC+ to power - 5V is best but 3V also seems to work for 3V microcontrollers.
Next, download the Adafruit LED Backpack library and the Adafruit GFX library from the Arduino library manager.
Open up the Arduino library manager:
Search for the Adafruit LED Backpack library and install it
Search for the Adafruit GFX library and install it
Once you've restarted you should be able to select the File>Examples>Adafruit_LEDBackpack>sevenseg example sketch. Upload it to your Arduino as usual. You should see a basic test program that goes through a bunch of different routines.
We also have a great tutorial on Arduino library installation at:
Once you're happy that the matrix works, you can write your own sketches.
There's a few ways you can draw to the display. The easiest is to just call print - just like you do with Serial
- print(variable,HEX) - this will print a hexidecimal number, from 0000 up to FFFF
- print(variable,DEC) or print(variable) - this will print a decimal integer, from 0000 up to 9999
If you need more control, you can call writeDigitNum(location, number) - this will write the number (0-9) to a single location. Location #0 is all the way to the left, location #2 is the colon dots so you probably want to skip it, location #4 is all the way to the right. If you want a decimal point, call writeDigitNum(location, number, true) which will paint the decimal point. To draw the colon, usedrawColon(true or false)
If you want even more control, you can call writeDigitRaw(location,bitmask) to draw a raw 8-bit mask (as stored in a uint8_t) to that location.
All the drawing routines only change the display memory kept by the Arduino. Don't forget to call writeDisplay() after drawing to 'save' the memory out to the matrix via I2C.
There are also a few small routines that are special to the backpack:
- setBrightness(brightness)- will let you change the overall brightness of the entire display. 0 is least bright, 15 is brightest and is what is initialized by the display when you start
- blinkRate(rate) - You can blink the entire display. 0 is no blinking. 1, 2 or 3 is for display blinking.