Summary of Dot matrix display
This article describes a DIY Dot Matrix Scrolling Sign using an ATMega328 microcontroller and LTR-747HR 5x7 LED matrices. The system employs three 74HC595 shift registers for column control, with signals amplified by ULN2003 drivers. It supports scrolling messages via AVR-BASCOM code compatible with ATTiny2313 or ATMega8 chips.
Parts used in the Dot Matrix Scrolling Sign:
- ATMega328 microcontroller board
- LTR-747HR dot matrix display (0.7 inch)
- Three 74HC595 shift register ICs
- ULN2003 amplifier
- Two 10 pin flat cable connectors
- AVR-BASCOM compiler software
- ATTiny Board or STK500 interface
This is a Dot Matrix Scrolling Sign. A Dot Matrix Display has an 5×7 led matrix with 5 columns and 7 rows. The display is controlled by the ATMega328 microcontroller board. The rows are controlled by PORTB of the microcontroller, while PORTD puts the data on the columns to make the characters. The Dot matrix display used here is the LTR-747HR and is 0.7 inch (17.8mm) high.
Circuit Schematic and PCB Layout
The circuit is stand alone and can be connected to the ports B and D off the AVR microcontroller. The circuit consists of three shift registers IC’s 74HC595 which switches each column of the displays sequentially on and off for 3ms. PORTB controls the the 74HC595. When a column is selected, the data for the column is put on PORTD, the signals from PORTB are amplified by the ULN2003, and switches the LED’s on and off. While each column is swithed on and off seqeuntially, the characters on the display are formed. The PCB contains all the parts except for the microcontroller part. The PCB has to be connected via the two 10 pin flat cable connectors to the attinyboard or the STK500 for example. You can buy the ATTiny Board at www.bizztronix.eu
Software
The program code is made with the AVR-BASCOM compiler. There is a program for the ATTiny2313, which can show several moving messages on the sign.
There is also a program that is made for the ATMega8 which is more extensive, with this program you can enter a text with maximum 40 characters in a variable in the program, which is shown on the display. It has also a bigger character set. Below you can download the software code
For more detail: Dot matrix display
- What is the size of the dot matrix display used?
The display used is the LTR-747HR which is 0.7 inch high. - How are the rows controlled in the circuit?
The rows are controlled by PORTB of the microcontroller. - Which components switch each column sequentially?
Three shift register ICs 74HC595 switch each column on and off for 3ms. - What amplifies the signals from PORTB?
The signals from PORTB are amplified by the ULN2003. - Can I enter custom text for the display?
Yes, the program for ATMega8 allows entering text with a maximum of 40 characters. - Which compilers are used for the project code?
The program code is made with the AVR-BASCOM compiler. - How does the PCB connect to the microcontroller?
The PCB connects via two 10 pin flat cable connectors to boards like the ATTinyboard or STK500. - Does the project support multiple moving messages?
Yes, there is a program for the ATTiny2313 that can show several moving messages.
