Scrolling text in LED dotmatrix display

Posted on Feb 6, 2014

Multiplexed displays are electronic displays where the entire display is not driven at one time. Instead, sub-units of the display (typically, rows or columns for a dot matrix display or individual characters for a character orientated display, occasionally individual display elements) are multiplexed, that is, driven one at a time, but the electr

Scrolling text in LED dotmatrix display
Click here to download the full size of the above Circuit.

onics and the persistence of vision combine to make the viewer believe the entire display is continuously active. In the above figure, the rows are negative and columns are positive. Now, if I connect a single column to positive 3V and a single row to negative (0v), then the LED in place of the intersection of the corresponding row and column will glow. Now, if we select a single column(means a + volt at selected column), say column 1 and multiple rows (means connect 0V to few selected rows), say row 1, 2 & 8, then the selected 1, 2 and 8 LEDs in column 1 will glow. Now if i shift the column(means shifting the positive voltage from column 1 to column 2), and if i change the row data, then the new data will be displayed in column 2. Now, if i continuously shift the column and provide row data corresponding to each column, then i can display the different row data (8 bit) in different columns. . So, if one frame(10 column shift) is completed within 1/16 th of a second, then due to the persistence of vision of our eye, we will feel the entire columns are activated at a time, and thus we will see all the ten -8bit data corresponding to the 10 columns, at a time. In the above circuit, the PIC16F877A provides the 8 bit row data. CD4017 is used to select the column one by one. Now, for shifting the column position, a clock is provided by the PIC to the CD4017. On every clock, the column is shifted. (from right to left in this...

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