LED Based Moving Message Displays
LED-based moving-message displays are becoming popular for transmitting information to large groups of people quickly. These can be used indoors or outdoors. We can find such displays in areas like railway platforms, banks, public offices, hotels, training institutes, nightclubs and shops. Compared to LEDs, liquid-crystal displays (LCDs) are easy to interface with a microcontroller for displaying information as these have many built-in functions. But these canâ€™t be observed from a distance and large size LCDs are very costly. 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 for displaying 16 characters or more at a time.
Moreover, programming will require a lot of data memory or program memory space. An external RAM may be needed to complement a microcontroller like AT89C51. However, if you use alphanumeric (16-segment LED) displays for the above purpose, programming burden is reduced and also it becomes highly cost-effective. You can make your own display panel consisting of 16 alphanumeric characters at a much lower cost. The circuit presented here uses 16 common-anode, single-digit, alphanumeric displays to show 16 characters at a time. Moreover, programming has been done to make the characters move in a beautiful manner. A message appears on the panel from the right side, stays for a few seconds when the first character reaches the leftmost place and then goes out from the left side. It displays 16 different messages to depict different occasions, which canbe selected by the user through a DIP switch.
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