For my final project in my digital electronics class, I am building an 8x8 LED matrix on perf board and hooking it to a breadboard which is powered by a breadboard companion. I have to make it display 3 different images. I have realized, however, that it is going to get pretty messy. I saw something here where he connected the grounds of the columns and anodes of the rows so that he could control each individual LED that way, then he made his circuit do this fast enough so that you couldn't tell that they were blinking. I have a very basic/limited variety of chips that are accesible (7-seg.s, AND, OR, NOT, R-pack, NAND, PLD's, etc. Basics...), and I was wondering, what would be some various ways to go about building a controller that would be able to display an image?

 

Maybe the PLD can do the job but the best solution would be a microcontroller.

 

The class is pretty basic (we've just been using those basic chips and the breadboards to learn how to count from 0 to F in binary, make an LED display each one, how to make it cycle through each number/letter using the BBC's clock and some flip-flops, and flip-flop basics), so we haven't used microcontrollers, and I don't know much about them. I'm not sure how I would even start to do this using a PLD either (we are using gal22v10's btw). If its gonna be pretty difficult to do with the stuff we have, I will probably just control each individual LED

 

If you want to display just two pictures then wire each row on the output of a NOT gate and use a SPDT switch to change between the pictures. The switch will control the inputs of the NOT gates.

Then use a decade counter and connect each column to one of its outputs from Q0 to Q7 and clock it with a frequency of 1 kHz.

In this way each column will be selected each time and the rows selected by the NOT gates will light.

 

So hook the input of picture 1 into one input on the SPDT and the input of picture 2 to the other input of the SPDT and run the output of the SPDT switch to the input of the NOT gate. Then run the NOT gate's output to the row (cathode) and do this for all 8 rows. I'm not really following this part too well. I'm not sure how you're saying I need to wire the inputs for the pictures either...

Also, I looked up decade counters since we haven't used them. Wouldn't it be possible (although "bulky") to make one out of flip-flops?

 

So hook the input of picture 1 into one input on the SPDT and the input of picture 2 to the other input of the SPDT and run the output of the SPDT switch to the input of the NOT gate. Then run the NOT gate's output to the row (cathode) and do this for all 8 rows. I'm not really following this part too well. I'm not sure how you're saying I need to wire the inputs for the pictures either...

Forget that idea, I though of it better and it won't work. You need to control each LED individually.

Also, I looked up decade counters since we haven't used them. Wouldn't it be possible (although "bulky") to make one out of flip-flops?

I never though of that but it should be possible to make one. However, I suggest you to buy one, they cheap.

 

I'm starting to grasp the idea a lot better now. I figured out how to make a decade counter out of a 74LS163 and a 74LS42. I'm going to run the clock input to a 555 chip running at 1kHz (the BBC's clock doesn't go very fast). Then I'm going to have certain columns light up as it cycles through each row. Now I just have to finish all the soldering, wiring, equations, etc.

If you have any suggestions let me know, thanks for the help so far

 

hi that1guy112,

i have a similar project to what you described above. i happened to come upon this page and i was wondering if i could ask you a few questions regarding your solution. i'm new at this forum thing... so i couldn't figure out how to send you a direct message.

thanks,
katie

 

Hello petey27. And welcome. Being new to the forums, I'll give you a hand at finding what you want.

You can check the date the posts you are responding to in the top bar of each message.

That1guy112 is long gone.

If you see a old post like this, you can click on the Original Posters name and see some information on them. For instance:

that1guy112
Last Activity: 05-04-2009 05:52 PM
Join Date: 05-03-2009

He joined on 5-3-09 and hasn't returned since 5-4-09.

There are some VERY knowledgeable people on this forum, so you can easily get some direction. The information is done in public exchange so others can learn from it. Allowing new members to private message right away would lead to a huge amount of mail that can help no one else. It also weeds out the spambots from advertising the crap out of everyone.

I would suggest starting a new topic explaining what you have done, or would like to do. Where you are, interms of location and how far you have gotten in the project yourself. If you have a schematic or wiring diagram, post it. It will help communicate what is right and what may be wrong.

Any part numbers to the components you have or want to use will be helpful.

You will find a wealth of information with a little more searching of the forums also.

[ed]
I searched for 8x8 led and came up with this:
http://forum.allaboutcircuits.com/showthread.php?t=28372

BMorse is also still an ACTIVE member, therefore after reading the info if you still have questions, you can mention the thread I posted in your NEW THREAD and will be able to get specific help.
[/ed]
Have fun.