Dot Matrix LED Displays
Dot Matrix LED displays have a 5 x 7 led matrix that contains 7 rows and 5 columns. The display is controlled by the AVR micro-controller. Rows are under control of PORTB of the micro-controller and PORTD puts the data on the columns to create the characters.
The circuit of this special LED displays is designed by using latest technology and can be connected to B and D ports off the AVR micro-controller. The circuit contains three shift registers IC’s 74HC595 that switches each column of the displays consecutively on and off for 3 ms. PORTB controls 74HC595. When a column is elected, the data for the column is put on PORTD, signals from PORTB are elaborated by the ULN2003 and switches the LED’s on and off. While each column is switched on and off sequentially, the characters on the display are created. The PCB have all the parts except for the micro-controller. This PCB is connected to the attinyboard or the STK500 through the two 10 pin flat cable connectors.
The program code of Dot Matrix LED display is composed with the AVR-BASCOM compiler. There is a program that called ATTiny2313 can show many animated messages on the display. There is also another program that is developed for the ATMega8. This program is most extensive. With this program, you can insert a text with 40 characters (maximum) in a variable of the program, which is shown on the LED displays. It has also a bigger character set.