Hi All,
I am working on a Rolling LED display. The display is 16 rows and 160 columns. I am using 8:1 multiplexing. The display is column switched. Iam using timer0 for multiplexing. The scanning frequency is 88Hz. Each column is on for a period of 1.25milliseconds.After a complete scan of 8 columns all the columns are off for the same period i.e. 1.25ms. During this period I roll the column data i.e. the data for column 2 is written to column 1, data of coulmn 3 to column 2 and so on. The rolling is smooth. The problem is it appears as if there were more LEDs on the board than they exist. If for example the character "I". This character is two column wide in the centre. When rolling it appears as if it were made of 4 or 5 LEDs. The physical pitch is 10mm while rolling it appears to have a pitch less than half this. If I increase the scanning frequency, this effect increases. The effect reduces when I decrease the scan rate. But if I go below 50Hz, then flicker starts. I know this has something to do with the persistance of vision but not able to figure out the cause neither could thin how to remove the problem. Does anybody suggest a scanning technique so that the characters look the same while rolling as they look when the display is steady?
Regards
Unmesh