hello all,

i'm new to this site and this is my first post.

i want to build a led matrix possible size 7 x 24.
In this i need to scroll a text or a message..

and i need to build this without using any microcontroller.
i can use basic logic gates,registers,counters etc..
please help me with any circuits or schamatics if available.

thanks in advance

 

Good luck. You'll need it. Sorry to sound defeatist, but it will be significantly more difficult to use logic gates.

Let's list what you'll probably need:

• String memory, to store the string you want to display
• Interface logic to program the string data
• Character ROM, to store the representation of each character
• Address generators for the character ROM
• Address generators for the output
• 168 output transistors. Or, you'll need to multiplex the display as well, so you may need graphics memory to remember the output of the display and logic to update the graphics memory.

If you're allowed to use FPGA's it may be an option. I would suggest checking if there are any dedicated display driver ICs.

The restriction on microcontrollers sounds like a course requirement. We won't do all your homework for you.

 

If you need to scroll the text, you are pretty much screwed. Static text is doable with a RAM (or ROM if it really is static), a counter and 24+7 transistors, but scrolling will be hard to achieve.

My idea would be a 24B RAM to buffer the "frame" that is displayed and constantly cycle it through the LED columns, and a ROM containg the string which will be frame-by-frame written to the RAM to move the text. Forget the character ROM that tom66 suggested, that would be way too complex. You simply write the whole string to the (EEP)ROM, where each byte represents one column of LEDs, and then display the right part of it via tha RAM part. The RAM and ROM definitely need to have parallel-access, serial is again way too complex without micro. The move from ROM to RAM will need to happen pretty fast to avoid flicker and other stuff to occur.

If you can´t use memory chips, then you will have to build them out of registers and other gates

 

Is this some kind of sick joke?

Punishment for bad behavior?

Is this a bet?

 

It sounds like a homework assignment that our OP wants someone to do for them.

 

I think an important piece in such a system will be some sort of character (E)PROM for storing the different symbols.

 

That depends on the assignement, it could be just storing the bitmap of the whole text area.

 

You say you have to do it without a microcontroller BUT are you allowed to drive it using a PC???????

 

Hey heres an off the wall idea from way back when most computers still contained ferite beeds and were probrammed directly with paper products.
Why not use a linier optical sensor array (FAX esqu) and 'read' the text ....
Are stepper motors on the cards.....
Programming would be quick .... scrawl it in thick black marker and shove it in the slot!
Al ... (Showing his age, and bezzare thought processes)

 

Good luck. You'll need it. Sorry to sound defeatist, but it will be significantly more difficult to use logic gates.

Let's list what you'll probably need:

• String memory, to store the string you want to display
• Interface logic to program the string data
• Character ROM, to store the representation of each character
• Address generators for the character ROM
• Address generators for the output
• 168 output transistors. Or, you'll need to multiplex the display as well, so you may need graphics memory to remember the output of the display and logic to update the graphics memory.

If you're allowed to use FPGA's it may be an option. I would suggest checking if there are any dedicated display driver ICs.

The restriction on microcontrollers sounds like a course requirement. We won't do all your homework for you.

yeah..ur right...
its a project i'm supposed to make
but thanx for the info, i'l try to design this usin a PIC ic
i'm not supposed to use this..but who cares...i'l use it any way

 

You say you have to do it without a microcontroller BUT are you allowed to drive it using a PC???????

wel i can use a PC...

 

Basically you will need memory, probably EPROM, with a sequential counter (actually 2 of them, one for the minor scroll on the immediate display, and one for the large scroll of the entire message. You should be able to do this with 5 chips, not counting programming the EPROM and drive transistors.

 

Well that makes it very easy. You just need to do a row and column select controlled by your parallel port. You can do scrolling. You can make it go backwards and forwards. You have a huge amount of options.

 

Forgot to mention you may need shift registers or multiplexers. Lot of options you can combine.

 

That was what I was thinking about. Given the shear numbers of 8 bit chips out there I don't see it being that hard. PITN to wire maybe.

 

any schematics regarding this will be very helpful.
please help me..

 

Do you have some method of programming a PROM, EPROM or EEPROM?

Without some kind storage like that, you will need a LOT of ICs, and it will take you a LONG time to build and de-bug it.

 

Homework has rules. We can help, draw block diagrams, but it is your homework. We can critique and offer suggestions but we would not be helping you doing your work for you.

How big did you want the display to be again? Think binary, 32 bits wide X 8 bits high for example, and how many characters total do you want (128 characters?).

 

i want to display "hello world"

 

Look at SIPO (serial-in, parallel-out) shift registers for starters.