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Scrolling LED Display

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Hi, does any here knows how to make a text scroll on a single 5x7 LED display the scrolling should be per row because only a single 5x7 will be used.

Thanks.
 

crust

Member
One of the university projects I worked on was such a device. It consisted of an array 7Hx50W of LEDs. (I think I used only 48 of the columns). I used a fairly low power micro (6811?). My approach used a series of 74595 (one bit for each column) driving a transistor. Then I used some high power transistors for each row (each row potentially drove 1A or so). Then I would load the shift registers, switch the row and latch the shift register at the same time. The only disappointment with mine was that the LED arrays I used were not "dense" enough.

Good Luck
 
You have your schematic please? Can I use the built-in or market ready 5x7 display?
 

crust

Member
mysemcon2000,

I'll assume you were responding to me? No, I no longer have the schematics, though I could draw up something quick and dirty. Basically, you can use the off-the-shelf 5x7 matrix displays that digikey sells. That is what I used (though I would have liked the LEDs to be oriented closer together).

Are you using a single 5x7 array of LEDs and want to scroll a message across just one unit?
 
I will be using only a single 5x7 display but the scrolling should be done one row at a time until the charcter is formed.
 

crust

Member
So if you use a single 5x7 matrix display, i would suggest using some type of microcontroller, perhaps an AVR or a PIC. Both of these can sink about 25mA per output which would allow you to directly connect the micro to either the rows or columns (depending on which one is the cathode). So that would use 5 or 7 pins of your micro. You could then use a 3-to-8 multiplexer to select which row/coloumn of the other axis you want to acitvate. (You might need to use a buffer or transistors for extra drive current).

Lets assume that you connect the micro directly to the 5 columns. Three other outputs drive a 3-to-8 mux which is connected to a 74XX series bus driver (for extra drive current ... might not need it depending on the current requirements of your led array). Then you just cycle through the rows activating the proper columns as needed. Depending on your circuit voltage you need some type of current limiting resistors. I would put them on the side with 5 (just less parts).

The last thing you need is the software to scan the display and a character set stored in your microcontroller rom.

good luck.
 
What I can't get is the algorith to make the display scroll one row at a time to show a certain character, I am using an 8051 Based Microcontroller DS5000T.
 

crust

Member
For instance, let say you intend to show the character "A" for 1/2 second. What you need to do is rapidly scroll through the rows lighting up the respective LEDs. If you light up each row fast enough, your eyes/brain will combine the image and give the impression that all the rows are simultaneously illumiinated. I dont recall my refresh rate, but I suspect it was around 30Hz -- I was illuminating each row 30x per second.
 
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