We normally use a simple static LED display screen to convey a message. Earlier, when we want to display large data, we used to change message for every few instances. Now scrolling displays are more preferred to static. By using a pre programmed controller, we can make LED display in scrolling way. We can also make LED to adoptable by using PC controller based system. Simple Outdoor LED Message Moving or Scrolling Sign Board, Electronic projects using LED Scroller Generator for outdoor digital signs, Marketable LED sign board with Message scrolling are the examples of the scrolling LED display.
Scrolling LED Display Working With Circuit Diagram
Let’s have a discussion about LED scrolling display with circuit diagrams. Scrolling LED display can be implemented in various methods. Two methods are widely in use, first one is decade counters and another one using shift registers. The shift register is easy to implement for beginners. Let’s discuss about LED using shift registers. Scrolling LED display panel is implemented by using microcontrollers like 8051, AVR and PIC micontroller. Here we discuss about implementing using 8051 microcontroller for simple electronic projects.
LED Dot Matrix Construction
When we want to construct LED Dot Matrix, lets know about how to drive LED and which resistance is added to protect LED. LEDs are two types
- High power LEDs
- Miniature LEDs
High power LEDs are costly, so generally we use miniature LEDs in practical experiments. Generally a red color LED can be made ON by using 2 or 3 volts. If we want to make LED to glow more 20mA current to flow.
Below figure describes about how to make LED using the 5v supply. If we connect directly 5v supply to LED, it may get damaged. For that, we connect a resistor in series with the resistor. Current flowing through the LED scrolling sign can be described as load current. For better brightness 20mA is needed to glow LED, so load current is 20mA and LED takes 2v to turn ON.
Using ohm’s law
R= (5-2) V / 20mA
R= 150 ohms.
R = 150 ohms,
(Driving an LED using 5v source)
LED Array Single Column
To construct an LED Array, entire cathodes are connected together and grounded. Each anode drives by the microcontroller. The microcontroller is programmed to generate different patterns on the LEDs. A total of 160mA current sinks into ground.
Construction of LED Dot Matrix
Using a single array of LED scrolling display board, we can generate different types of patterns. If we arrange the LED arrays side by side with multiplexing technique, it generates letters, symbols, numbers, pictures, animations also. This LED Dot Matrix can be constructed by connecting all the anode terminals of LED’s together in each row and all the cathode terminals are joined together in each column.
Anode Circuit in LED Scrolling Board
Some microcontrollers don’t have enough output voltage/currents to drive the rows of the LED scrolling display board. Hence, we need to place a transistor array or a latch between the led matrix and microcontroller. Usually for LED Scrolling board, the latch is enough to provide sufficient current. We can use 8-bit latch (74ls573). Each output of the 8-bit latch is able to provide current greater than 20mA, Which is enough to produce sufficient brightness to the LED.
LED Dot Matrix To Work
LED scrolling message display matrix can be made to work, by connecting all the anodes to a microcontroller and the columns are connected to shift register (74LS164). Every column contains ‘N’ LED’s so that the total current flowing through the column is the sum of current flowing through each LED. The current flowing through each LED is 20mA and the total current is N*20mA .The shift register is not capable to sink such a large current n*2mA, Here we need a large current sinker (IC ULN 2803) which is capable to sink 500mA current.
For more detail: LED Scrolling Display Project Working With Circuit Diagram