??? 08/03/04 07:28 Read: times |
#75312 - RE: Need help with LED display Responding to: ???'s previous message |
hi,
the two (2) pictures u added to explain the program u sent me earlier didn't open (show). Yeah - unfortunatelly, free space of my homepage here has been endeed and so I posted links to photos placed on another web resource. Due some reasons, my provider does not allow to see pictures accessed indirectly, sorry. To see them, just press right button over frame where picture should appear, and select menu "Properties". In opened window, catch the picture link address, then put it into browser input address line directly. about ur question : "do u have experience with column/row multiplexing" ? i do not. what i know is what i have read so far You see, let assume you have eight one-colour LED dot matrixes; each one is organized as "7 rows x 5 columns". By other words, each matrix has 35 dots, so eight matrixes contain all 280 dots. With standard way, when the each dot has been controlled with own output bit latched with an register, it requires 35 8-bits latch registers. Thanks God, there is another technique called "dynamical refresh", or row/column multiplexing. First of all, you should look at organization of LED dot matrixes you have there. They may be column anode or column cathode. This is main thing you may pay attention on: depend on the organization you have to calculate the number of registers and transistors for multiplexing. There is another very important thing as well. If you create scroll display based on LED dot matrixes, you must pay attention on the effect called inertia of eye vision. Due lack of time, I will not explain it here. Just remember some rules: - do refresh all dots within 10ms (100 times per second) or quickly to avoid flicker effect; - smooth scroll requires 25 or more movings per second. Otherwise people will see discrete steps; - the speed of scroll must not exceed the refresh speed otherwise parts of text/image will disappear randomly. If you need faster scroll then just do it at two, three etc colums per time (skip technique); - for right-to-left scroll, do refresh only by rows at direction from down to up. The direction of refresh defines the inclination of text/image. If for right-to-left scroll you do use refresh by columns then text/image will "breathe" during scroll (some columns may disappear randomly; scrolling looks like it has not stable speed etc). Now, when you will accept the theory, please welcome back for practice. Regards, Oleg |