LED-based moving message displays are becoming popular to quickly transmit information to large groups of people. These can be used indoors or outdoors. We can find such exhibitions in areas such as railway platforms, banks, public offices, hotels, training institutes, night clubs and shops. Compared to LEDs, liquid crystal displays (LCDs) are easy to interface with a microcontroller to display information as they have many built-in functions. But these can not be seen from a distance and large LCD's are very expensive.
LED-based displays can be of two types: dot matrix and segmental. If you implement a moving message display with multiplexed dot matrix LEDs, it will be very costly to display 16 characters or more at a time. In addition, programming will require a large amount of data memory or program memory space. An external RAM may be required to complement a microcontroller such as AT89C51. However, if you use alphanumeric indicators (16 segment LEDs) for the above purpose, the programming load is reduced and also becomes very cost effective. You can create your own display panel consisting of 16 alphanumeric characters at a much lower cost.
The circuit presented here uses 16 common anode alphanumeric displays and a single digit to display 16 characters at a time. On the other hand, the programming has been done to make the characters move in a beautiful way. A message appears in the panel from the right side, it remains a few seconds when the first character reaches the leftmost place and then exits the left side. It displays 16 different messages to represent different occasions, which can be selected by the user through a DIP switch.
A dot matrix display is a display device used to display information about machines, clocks, rail output indicators and many other devices that require a simple display device with limited resolution. The screen consists of an array of light points or mechanical indicators arranged in a rectangular configuration (other shapes are also possible, although they are not common) so that when you turn on or off selected lights, you can display text or graphics. A dot matrix controller converts a processor's instructions into signals that turn on or off lights in the array so that the required display occurs.
