ARD-MAX7219-8 8-Digit SPI Display Module – Red
This small module allows you to control two 4-digit 7-segment displays with one SPI port, saving you a lot of pins in the process! Five pins are used to control the display:
VCC → 5V
GND → GND
DIN → P00
CS → P01
CLK → P02
Note: this module has no polarity protection. You’ll fry it if you wire it backwards!
Resources:
Arduino Playground: http://playground.arduino.cc/