# 8x8 dot matric 3mm diameter

In this Instructable website, someone has made LED matric of many 8x8 Dot-Matrix.

His instructions are not clear for me about how he manage his output from his controller to all theses led. Does anyone can explain me OR give me a link to a website where I could ask this question (it might not be appropriate here, but keep in mind that I would do it with Arduino board if I could understand). By the way, I have found on ebay this Dot-Matrix and it cames with a PDF but I can’t undestand more how to make it works.

These Led Matrices are really easy to understand. Have you seen the picture of the schematics in the link you posted? The negative sides of each led in a row are connected together. The same with the positive side, all the leds in a column are connected together. So, let’s say you want to light up the led in the 3rd column and the 2nd row, what do you do? You conect the 3rd column to the negative, and the 2nd row to the positive. That simple!

Now, some thinkering. What are the restrictions that this kind of design imposes?
A tip: the solution to overcome the problem, is the use of the POV (google it!).

Hope this helps you! Sorry about my english… trying to improve it!

I think I can have problem with the power that it might require furthermore, if I require to use 10 of theses Matrix I will need to have Shift Register. In the link I posted, it uses and something to adjust the current, but the link is so old that the component that he uses doesn’t exist anymore. I do not understand if it really necessary…

Sorry daok that schematic is not correct. There appearers to be no MIC2981 in the schematic. Therefore if you have ten of these they will overload the processor’s output pins.

The idea is that you have a shift register for each matrix. But you only need one processor, he leaves you to work that out.

OR
Does this design take 10 processors, in which case you don’t need the drivers?

It’s not at all clear and I am not a beginner.

Alright so two questions come into my mind. Where can I learn to know that it overload the processor. I would like to understand that. Second question, if it overload the processor, what type of component should I use between the processor pin and all the DotMatrix, it must have something that is possible to do? :-/

I found something in this website for Arduino:

The rows are handled by an ULN2803, an array of darlington transistors. This chip is used to sink the current of the activated row. If every LED in a single row is activated, the current for this row will sum up to 320 mA (16 * 20 mA). Definately too much for a single pin of a microcontroller. The ULN2803 is able to sink up to 500 mA per channel and cheap (about 30 euro cent).

So this ULN will take out the power fast this way it won’t overload the pin right? I will need 1 for each DotMatrix right?

Where can I learn to know that it overload the processor

On virtually every discussion of the Arduino it is mentioned that the current limit on the output pins is 40mA. Failing that the data sheet for the processor.

The ULN2803 is able to sink up to 500 mA per channel

Yes but you can’t use all the channels at the same time at 500mA only a total of 650mA can be switched at any one time for any one chip. See:-

http://www.thebox.myzen.co.uk/Tutorial/Power_Examples.html

1 for each DotMatrix right?

No you only want to drive the rows with them to stop them from overloading the processor.

The point is that the simple circuit you saw is not the full story I think you have a lot to understand before you can embark on this project. Start off simple with just one matrix, there are plenty of tutorials to show you how to do this. Then only when you have that working think of expanding it. Look in the playground.

Thx for your input. I appreacite. I plan to start progressively with 1 matrix… but I will buy the whole thing so I have to start planning.

I feel that I am not really at my place here : :-/ I might be too much newby for this community. I have more success with the same question at Sparkfun.

Sorry for all these newbies questions and thanks for the link, this will help me to understand.

daok,

In my opinion, there is no need to feel out of place here, or too much of a newby.

I can understand that this board will feel different than say Sparkfun’s. It is different because it is much more focused, it has much more “history”, many more “experts”, and many more questions to answer.

As such, there is probably a higher expectation that people have done some “homework” before posting. Doing this, makes the questions easier to answer accurately, and means that less time is taken asking you questions.

I’ve never seen a more helpful group of people in my life. So hang in there!

It looks like you started with a poorly documented example. You could try to get more info from the author (doubtful) or you can discribe what you need to do differently.

Alright, I will be back when I will be more in the programming part. For people that is interested about the idea here is the thread on SparkFun about all component and all newby stuff about how it works.

Hi daok, I feel some anger on your answer. Do you think the persons here don´t like to help with newbie things? I´m asking this cause, altough I don´t post too much, I´ve been reading the forum for a while, and I´ve never felt that way.
If anything on my answer denoted I´m unwilling to help, that was not what I meant. (I don´t fell comfy about the construction of this phrase - in the grammar matter- can anyone say if the sentence is right?)