DRIVING A LIGHT EMITTING DIODE BI-COLOUR MATRIX DISPLAY
There are many inexpensive 8x8 LED displays available but these usually require some additional driver software or hardware chip to make them operational. However, Adafruit has developed a range of LED displays with accompanying driver chips alongside software libraries for the Arduino.
There are many different devices supported - 8x8 single and bi-colour matrix, 4-digit 7-segment, LED bar, etc. These devices usually come as a partially assembled kit with only minor soldering required. The kit comprises the LED display, a single row header and a small PCB with a surface mounted Holtek HT16K33 chip already fitted. The interface is I2C, which means only four connections are required: 0V, +5V, clock and data. Each device has three pairs of solder pads that can be connected to set the device's address - 3 bits allows 8 devices on the same I2C bus with address 0x70 to 0x77 inclusive. Leaving a pair unconnected gives a value of 0; connected, 1.
If you choose to use the 1.2" 8x8 single colour modules, there is a labelling error on the backpack PCB and the solder pad address labels A1 and A2 are swapped.
Addressing Schema
Arduino Pin | LED Backpack Pin | I2C Name |
---|---|---|
GND | 1 | GND |
+5V | 2 | +5V |
A4 | 3 | Clock |
A5 | 4 | Data |