ABSTRACT

Light Emitting diodes have been around for some years now. Advances in technology have now made it possible for Light Emitting diodes to transform from devices earlier used as indicators due to their low light output to devices that can be used for lighting. Today, light emitting diodes are so bright with high lumen output that they can be used for virtually any kind of application. In this project, We use a number of high lumen light emitting diodes arranged in a dot matrix format to show the current time and ambient temperature. Due to the high lumen output of the LEDs, the display can be used both indoors or outdoors.  Working on the strength of a microcontroller (PIC16F873) and other components such as serial registers, transistors, temperature sensor integrated circuit; we are able to build a complete display system that can display the time of day and temperature, as well as allowing users to interact with it to set the time.

MODE OF OPERATION

Block diagram of the LED matrix digital clock and temperature display

The microcontroller is the heart and soul of the project. The microcontroller is responsible for sending the appropriate data to the shift registers and to the row drivers to create an image on the dot matrix display. a real-time clock has been implemented in the microcontroller through software. Certain registers inside the microcontroller are used to hold time data. The microcontroller reads the values of these registers and processes it to a form that can be displayed on the dot matrix display. Every image displayed on the dot matrix display is first prepared in RAM. The microcontroller then converts the data into a serial stream and sends it to the shift registers on row at a time. To display a complete image, the shift registers are first loaded with data for the first row. The microcontroller then activates that row to display the data on the shift registers on the LEDs. Next data for row2 is loaded and the row transistor is activated to show the data. This continues until the last row data has been loaded and displayed. And then the cycle is repeated. It should be noted that this happens at very fast rate that it appears to the human eye as if the whole image is displayed at once. The microcontroller also continuously scans each of the three input buttons to know when they are pressed. once a button is pressed, the microcontroller processes the button press and displays it on the dot matrix.

Arrangement of LEDs in a dot matrix display connection

The arrangement of the LEDs allows for random access to any led on the matrix. Each LED or pixel has an address that can be accessed by the microcontroller through a shift register cascade. By accessing several of the LEDs at a speed that is fast enough for the eye to notice, we can create the illusion of a steady display. This is known as persistence of vision.