INTRODUCTION
An LED dot-matrix display is a display device used to display information on machines, clocks, Bus Departure indicators and many other places requiring a simple display device of defined resolution.
It is also called a multiplexed display - meaning a kind of electronic display where the entire display or LEDs are not driven at one time
rather a set of LEDs are displayed (in most cases column-wise) one after the other. But due to the electronics and the persistence of vision combine and achieved in software, makes the viewer believe the entire display is continuously active.


In this thread, i am going to show you how to build a 7 row by 5 column by 4 page LED Dot Matrix Display.

One advantage of this design over other LED Dot matrix is that it achieves both a column and row scan.
Meaning that only a single LED is ON at
a particular point in time in the entire display. In that case, we don't need any transistor or transistor IC for any form of amplification since our LED needs about 25mV while our uC (Microcontroller) can source about that same amount of current.
But then this comes with a disadvantage that more time is required to light-up a column unlike when it was a column scan alone. The implication of this is that we could only but achieve a lesser number of pages to avoid any noticeable flickering effect.

Let's get down to business

Tools and Components needed
Assuming you have other basic electronic kit, these are the components required:
Hardwares
1. 5x7 LED Dot matix board - 4pcs
2. 4017 IC - 3pcs
3. Microcontroller (PIC 16F877A) - 1pcs
4. 7805 IC - 1pcs
5. 1N4001 diode - 4pcs
6. 4.7k resistor
7. 10MHz Crystal Oscillator -1pcs
8. Vero board and/or breadboard
9. 470uF Capacitors - 2pcs
10. 230-12V step-down transformer
11. Connector (Wire).

N.B:
1. You can actually design you own LED Matrix board, unfortunately i won't be covering it in this session.
You can checkout Aliexpress for a matrix board if it happened you can't find it here in Nigeria. It will actually save you lots of time and stress.

2. A 230-9V Transformer will work as fine but in cases of PHCN low voltage, you might obtain as low as 6-7V at your transformer's secondary and when you subtract the voltage drops from two rectifying diodes, at the end you will be having about 4.8-5.8V and this is less than the Minimum Vin for our 7805 voltage regulating IC, hence resulting to about 3V supply to power our uC.

Software Programs
1. ISIS Professional - for simulating your design on PC
2. MikroC - for writing C program for the uC

Nice. I'm interested. Sitting tight.

bigtt76:
Nice. I'm interested. Sitting tight.

Thanks for showing interest
More comments like this will motivate me to go on.

How a LED matrix display works

In the picture below, the rows are wired negative (indicated with blue colour) and columns are positive (red colour).

This means that all negative pin(shorter leg) of LEDs in a particular row are wired together same as all positive pin in each column as indicated in the picture below.

Now, if I connect a single column to say positive 3V and a single row to negative (0v), then the LED in place of the intersection of the corresponding row and column will glow (not so?).

Now , if we select a single column(means a +ve volt at selected column) , say column 3 and multiple rows (means connect 0V to few selected rows), say row 2, 4 & 8, then the selected 2, 4 and 8 LEDs in column 3 will glow.

Now if i shift the column(means shifting the positive voltage from column 3 to column 4), and if i change the row data (i.e making row 1, 5, 7 at 0V) ,then the new data will be displayed in column 4.

Now, if i continuously shift the column and provide row data corresponding to each column, then i can display the different row data (8 bit) in different columns.

So, if one frame(i.e. 20 column shift - remember we have 5 column per page by 4pages = 20column) is completed within 1/16 th of a second (62.5millisecond) , then due to the persistence of vision of our eye, we will feel the entire columns are activated at a time, and thus we will see all the twenty 8bit data corresponding to the 20 columns , at a time.

Meaning that if a set of 8bit data represents a character, say 'D', then we will see letter 'D' in the display.

I dey follow

pls proceed

Weldone bro. Continue we are following you

In this design, a decade counter is used as a shift register to scan through the columns at every clock signal.
Since the output of a decade counter is positive (i.e. ONE) , we are going to need a negative (i.e. ZERO) as our data bit sent by the microcontroller in order to display our desired character.

Technically, we can say our Decade counter sources current, while our uC sinks current - as indicated with the arrows.

Displaying a still character

We are going to learn how to display a still character first of all in order to get the concept of how a dot matrix display works.

Let's take an example, where we have to display letter 'D'. Doing so, it means we have to send five consecutive clock pulses to the clock input of 4017 decade counter. Each clock pulse is accompanied with these corresponding data bit:
11000001, 10111110, 10111110, 10111110, 10000000

What i mean here is that:
4017 clock pusle _______________ Corresponding uC data bits
1st________________________________ 11000001
2nd________________________________10111110
3rd ________________________________10111110
4th ________________________________10111110
5th ________________________________10000000


Note that my clock pulse begins from right to left while i start reading my data bits from bottom to top (just my preferred convention).
Note also that from the diagram below that the first pin(starting from bottom to top) of the uC is not connected to anywhere. Remember we have 7 rows, whereas our uC is an 8bit device, in essence, we have to always read that pin as 1 to complete our data bit eight!

Please questions are entertained.

Good work bro, but why are u using 4017 it is only good for just 10 columns. If we need more than that we have to cascade the 4017 which u and i know thats its not easy to do.

I dont mean to disrupt your tutorial but i think using shift register will be easier than a decade counter. Shift register like 74hc164, 4094, 74hc595 etc

Savotech:
Good work bro, but why are u using 4017 it is only good for just 10 columns. If we need more than that we have to cascade the 4017 which u and i know thats its not easy to do.

I dont mean to disrupt your tutorial but i think using shift register will be easier than a decade counter. Shift register like 74hc164, 4094, 74hc595 etc

Thanks for the comment bro.
Yes, you are right. 4017 requires additional AND gate to cascade but you can tweak it in your software program. For example if i want to use three 4017, i will have to tap from 3 different pins of my uC to serve as individual clock source, then i can take care of the cascading myself from the program.
I actually started with 4017. I have studied the shift register (74HC595) in the past to design a LED matrix display but at the end i still find my 4017 easier & handy for me (Maybe cos i started with it).
I noticed that with 4017, i am only concerned with my clock pulses, while with 74HC595, from what i studied, ii will have to be concerned about Clock and data shifting (enlighten me if i'm wrong).
But one advantage of 4017 is that it is readily available in the market.

I'm sorry for my slow pace .... i will be back soon to edit and update this space.
More comments and questions....

chemystery:
Thanks for the comment bro.
Yes, you are right. 4017 requires additional AND gate to cascade but you can tweak it in your software program. For example if i want to use three 4017, i will have to tap from 3 different pins of my uC to serve as individual clock source, then i can take care of the cascading myself from the program.
I actually started with 4017. I have studied the shift register (74HC595) in the past to design a LED matrix display but at the end i still find my 4017 easier & handy for me (Maybe cos i started with it).
I noticed that with 4017, i am only concerned with my clock pulses, while with 74HC595, from what i studied, ii will have to be concerned about Clock and data shifting (enlighten me if i'm wrong).
But one advantage of 4017 is that it is readily available in the market.

You are right, there are many ways to arrive at the answer and if 4017 is d way easy for you, it is ok. My own past experience when wanting to design 128 colomn tells me that 4017 is not feasible because according to what you said, if you tap each clock from the uC you will need more IO port.

Apart from the problem that 74hc595 is not available (but available in lagos), 74hc595 is d best. The data shifting might be complex but you can write the program once and for all. So when adding more coloms u dont need any additional pin from the uC.

At the end of your tutorial i will post my circuit simulation, and software written with PIC C using CCS compiler if you will permit me.

here is what i made out of on 4017 ;Dhere is what i made out of on 4017

farulz:
CAN SOMEONE TELL HOW TO GET THE PIC PROGRAMMER KIT IN HERE IN NIGERIA

Www.hub360.com.ng they deliver anywhere in nigeria or call 08063404828

This are some of various display i have made. I have made up to more than 20 different types, from monochrome to 7 colors to full colors.

Savotech:


Www.hub360.com.ng they deliver anywhere in nigeria or call 08063404828

Is It Free Delivery?

Nice Work Savotech, Can U Plz Help Me Out With The Creak Version Of Protues

Savotech:
This are some of various display i have made. I have made up to more than 20 different types, from monochrome to 7 colors to full colors.

Bro, between 5mm led and 10mm led, which will you recommend for a better display?

I want to create one too but a static display (not scrolling).

Jazzman01:


Bro, between 5mm led and 10mm led, which will you recommend for a better display?

I want to create one too but a static display (not scrolling).

Bro... It depends on your design application, if its indoor or outdoor. Then depends on the size.

If its indoor a small pitch like 5mm or less will be ok