The MAX7219 is a Integrated Circuit that can drive 64 individual LED's or up to 8 digits of 7-segment display's or a LED matrix of 8x8. The driver implements a SPI interface that can be controlled from a microcontroller using only three I/O pins.

The IC itself has 24 pins. An extensive datasheet for the IC is available from the Maxim homepage. The IC in this project is used to drive a 4 digit 7-segment display to show the time. The display is of the common caythode type. The ATMega328 microcontroller is used to control the 3 pin SPI interface.