# Displaying Alphabet Letters in a 5 x 5 Led Matrix using basic gates

#### kran27

Joined Oct 17, 2016
5
Good day to everyone.
I am a newbie here, can someone help me with the project I am working?
It is making a circuit that will display the letter of alphabets one at a time in a 5x5 Led Matrix but without using any micro-controller...

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#### dl324

Joined Mar 30, 2015
13,141
Welcome to AAC!

Is this homework?

#### AlbertHall

Joined Jun 4, 2014
11,506
Are you allowed an EEPROM?

#### joeyd999

Joined Jun 6, 2011
4,477

#### AnalogKid

Joined Aug 1, 2013
9,361
The problem is one of translating from one code to another. The ASCII code for a letter is 6 bits, but for each letter there are 25 output bits that must be defined as either high or low. The total number of output bits is 64 x 25 = 1600, but only about 1/4 of them are 1's.

There are many ways to decode/encode this. One is to notice that many of the symbols have similar strings of 3, 4, or 5 bits (1's) in a row. Taking a clue from how compression algorithms work, you could set up some fixed output strings and link to them as needed.

ak

#### WBahn

Joined Mar 31, 2012
26,398
The problem is one of translating from one code to another. The ASCII code for a letter is 6 bits, but for each letter there are 25 output bits that must be defined as either high or low. The total number of output bits is 64 x 25 = 1600, but only about 1/4 of them are 1's.

There are many ways to decode/encode this. One is to notice that many of the symbols have similar strings of 3, 4, or 5 bits (1's) in a row. Taking a clue from how compression algorithms work, you could set up some fixed output strings and link to them as needed.

ak
My guess is that this would result in a big mess when implemented with basic gates, which seems to be what the TS is looking at. If the TS can't use some kind of memory to store a LUT for the font table, an alternative could be to make a matrix table with resistors/diodes to set the state of the entries. Would still be more ungainly that I'd want to use for the entire alphabet, but if they only need to demonstrate the concept with a small handful of characters it might be reasonable.

#### WBahn

Joined Mar 31, 2012
26,398
Good day to everyone.
I am a newbie here, can someone help me with the project I am working?
It is making a circuit that will display the letter of alphabets one at a time in a 5x5 Led Matrix but without using any micro-controller...
Note that in your font table there's no difference between upper and lower case 'S'.

#### joeyd999

Joined Jun 6, 2011
4,477

#### WBahn

Joined Mar 31, 2012
26,398
I doubt that is too viable for the TS. I would imagine that getting the physical cores is not too easy these days (could be wrong) and while trying to find workable substitutes might be interesting and educational, it is probably not too practical for a project like this. Even if he succeeding in that, the assembly of the core matrix would take some time and then he would need to design/build the drive circuits to program and probe the elements. A pretty significant undertaking for someone at the level the TS would appear to be at.

#### dl324

Joined Mar 30, 2015
13,141
The only restriction mentioned was not using a microcontroller.
without using any micro-controller

#### joeyd999

Joined Jun 6, 2011
4,477
I doubt that is too viable for the TS.
I know -- but the principle is identical to a ROM based CG. I am hoping that the TS gets the idea that he needs some form of memory -- without explicitly saying it.

#### WBahn

Joined Mar 31, 2012
26,398
I know -- but the principle is identical to a ROM based CG. I am hoping that the TS gets the idea that he needs some form of memory -- without explicitly saying it.
Oh, he doesn't HAVE to have any memory -- it can be done with a big, ugly mess of combinatorial logic. But at some point it becomes less painful to start seeing if that pile of washers can serve as cores than to put together the logic.

#### WBahn

Joined Mar 31, 2012
26,398
The only restriction mentioned was not using a microcontroller.
Yep. That's the only restriction he MENTIONED, which is why AlbertHall's question is so relevant.

#### joeyd999

Joined Jun 6, 2011
4,477
Oh, he doesn't HAVE to have any memory...
25 six input K-maps didn't even cross my mind as a viable solution.

#### WBahn

Joined Mar 31, 2012
26,398
25 six input K-maps didn't even cross my mind as a viable solution.
To do by hand, I would most definitely agree, though as a group assignment in a class of 25 or so students, it's not bad. In fact, I could see an assignment that required each student to build the circuit to drive one or even a few of the LEDs and then have them all bring their circuits together to drive the matrix. Perhaps a group of five students with each student being responsible for one row of the display. That would allow the students to look for ways to optimize their logic a bit by sharing pieces of solution between pixels within their assigned row.

Depending on the course and the objective of the exercise, having students write a program to generate the logic might be quite reasonable (not that I think for one minute that this is what this particular assignment has in mind).

#### AnalogKid

Joined Aug 1, 2013
9,361
25 six input K-maps didn't even cross my mind as a viable solution.
It's not as bad as it sounds, but I don't want to give the TS the answer.

al

#### absf

Joined Dec 29, 2010
1,949
May be you can start by displaying the first alpha "A" in your table like this.
I program the 2732 using my 8051 assembler to generate a BIN file.

If the EPROM is not allowed, you might think of a way using address decoders and diodes to form the data for the characters thus replacing the eprom.

But this type of job is best done using a mcu...

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#### kran27

Joined Oct 17, 2016
5
Yep. That's the only restriction he MENTIONED, which is why AlbertHall's question is so relevant.
Our prof said that we can only use the gates that he discussed from us ; AND, OR, NOT , NAND, NOR, XOR, XNOR, BCD to 7Segment. I tried to get the functions in each output using truth table and karnaugh mapping, but it was a very long work to do. Is there another way of getting this instead of using k-mapping?

#### joeyd999

Joined Jun 6, 2011
4,477
Is there another way of getting this instead of using k-mapping?
There is software and online tools that can do this for you. Would your prof consider this cheating?

I don't think I would for such a large (and redundant) problem.

Are you sure you understood his instructions? It seems like an awfully large project to complete independently and by hand. And the incremental returns (accumulated experience) will diminish with each successfully completed K-map.

It's like asking a business student to learn double-entry accounting by trudging through dozens of similar transactions.