Hello,

As some of our members stated it is a homework assignment, I moved it over here.
To the Topic Starter:
What have you done upto now to work on your project?

Bertus

 

Ok, the specifications as I understand them as they have dribbled in:
The unit must have a 7 x 24 led matrix. (presumably 7 high x 24 wide)
The unit may not contain a microcontroller
The unit may be driven by a PC
(so far, there is no requirement as to the form of the drive -- raw, ascii, etc.)
The unit may use logic gates, registers, counters, etc.
(so far, there is no requirement as to the implementation of the gates/etc. (descrete tubes/transistors, IC's, relays, etc.)
The unit must scroll the text "hello world"
(so far, there is no requirement as to whether the scrolling may/must be done character by character, or led column by column)

Method 1:
Use a great big huge giant gob of eproms, gates, registers, static rams, character rom, clocks, etc. of any kind. There must be hundreds ways to do it -- pick one. After a few months and couple kilobux you will have a working unit.

method 2:
There is no requirement to use ascii (or any character coding/decoding), so don't. Use 24 7-bit shift registers connected to 24 7-bit drivers connected to the 24 columns of the led matrix. A switch selects a "scroll" clock or a manual "load button". In the "load position, seven spst switches place a "lit" or "unlit" into the current register. The "load" button strobes the switch positions in and advances to the next register to be loaded. So in the first row, you would put 7 "lits" in the register for the vertical bar of the "h". In the next reg, put one "lit" in bit 3, then bit 4, bit 3, finally bit 1 and bit 2 together. The first 5 registers will now have an "h" in them -- no character code needed -- just a bunch of lighted leds. Continue on with the rest of the message. Oops, right! -- you can't fit "hello world" into 24 columns. No problem, use as many 7-bit shift register cells as needed, but only 24 need be conneced to drivers.
Obviously, if you wan't to cut the parts-count/reprogramming-time you can do some multiplexing, store the text pattern in eprom, etc.

method 3:
This would be my favorite method but I'm still working on it...
Get a hundred or so old surplus telephone selector relays. These things are a 7-pole, 10-throw switch that is advanced one throw each time the solenoid is pulsed. We will be pulsing a bunch of them at the same time so we better get a 50 amp power supply while we're at it.
There are 11 caracters in the string "hello world" (plus a space)... Of those, only 7 are unique ...
...Ok, ok! So that one sucks!

Method 4:
The PC thing is obviously the way to go. A single simple parallel port has 12 output bits (normally 8 character data and 4 for strobe/control). Use 7 bits for the columns, the remaining 5 bits (2^5 = 32) are more than enough to multiplex the columns.
Looks like a fun (even if not practical) project.

Enjoy!
Teri

 

I did a project similar to that it's pc based, well the difference is that you have more LEDS and your's display a scrolling message while mine just displays a letter, though I can make a scrolling message i just need to change my program. Well, I did use a shift register and the PC's parallel port. I use msdos debug in programming you just need to call on the parallel pins. The scrolling message is merely delay. Well if I use msdos debug with that circuit of yours, to display "HELLO WORLD" my program would be so long...well you could use other language I suppose. But if you want to use PIC there are tons of tutorials in the web for scrolling LED display using PIC

 

thanku,
i've decided to make this usin a pc parallel port.