LED Matrix Question

[SteveB]

Ok, so I am correct in the assumption that the microcontroller is connected to the left of the EEPROM on the schematic?

Yes, this is correct. The pin arrangement is as follows:

1- N/C          10- N/C
2- N/C          9- N/C
3- Data         8- Clock
4- N/C          7- N/C
5- +5V          6- GND

I've been told that this is an intermediate to advanced programming level for the PIC?

Yes, but not insurmountable for a beginner, if approached in a building block manner. The basic communication in the circuit is not too complicated. The algorithms for the display may be a little tougher.

Is there anything you recommend me reading so I can program this?

Well, I can only speak for myself. I read through Myke Predko's book, "Programming and Customizing PICmicro Microcontrollers." (It is a little dated, and deals with assembly, but good initial explanation on the internals of the PIC. He also uses "psuedo code" a lot, so it's not too bad a transition). After that, get into the datasheets, for both the PIC, and other components. For PBP, there are examples all over the place for specific tasks. MeLab's own site has a nice set of example files.

A quick summary:
a) Know the PICmicro controller. (What can it do, and the basics of how)
b) Understand how the components work together in the circuit (Like the I2C comm)
c) Use PBP to get the PIC to do it’s job.

Rather simplistic, and very much my own experience/opinion.

Or any sites that offer custom program solutions for $$$?

I can’t really speak to this. Others may help.

SteveB

[Dave]

mekohler, I might be blind but, I don't see any schematic, only an overlay for a PC board....
I may be able to help as I have used PCF8574A's for many products in the past.

Dave Purola,
N8NTA

[mekohler]

mekohler, I might be blind but, I don't see any schematic, only an overlay for a PC board....
I may be able to help as I have used PCF8574A's for many products in the past.

Dave Purola,
N8NTA

You are correct, I didn't upload the schematic. That is here:

http://www.injektilo.com/PICHelp/schem.bmp


I have a feeling that jumping straight into this form of the project might be too difficult (considering my time constraints). I have come across a more common LED Matrix layout, and I have uploaded the pictures and code here:

http://www.injektilo.com/LEDMATRIX/

Again, I won't be using a 5x7 display, but a handmade 5x5 one. If I use this, it seems as though all the work is done for me (hehe).

My only question is....I want to replace each SINGLE LED with 5 LED's in PARALLEL (since I need to shine this through a diffusive plexi material, so I need the brightness and spread of light). Since they are in parallel they will each receive the same voltage as the single LED...but what about current? Would I need one resistor for each LED in the "parallel cluster" ?

My friend says: the important bit is that each LED should have its own resistor. Otherwise only the LED with the lowest internal resistance will light.

If so, what equation governs the value of each resistor? Argh! I just want to get this project I started over with before I move and then start my serious and gradual study of PIC programming.

Sorry for the change of course (or possible change). Again thanks for all the help guys!

[Ioannis]

No, you cannot parallel LEDs Diodes or Bipolar transistors (only FET). Since each of them is not a resistor the current cannot be shared among them. You sure need a resistor in series.

But you already have post this as in the link http://www.injektilo.com/LEDMATRIX/8...%20Example.JPG

Ioannis

[Dave]

mekohler, Why not series connect the LED's and use only 1 resistor. 1.8 volts x 5 = 9 volts. The driver you have is open collector so you can use 12 volts for the LED source and use say a 150 Ohm resistor in series and that will give you 20Ma. for the string.

Dave Purola
N8NTA

[Ioannis]

Thats what I meant but was not very clear. Anyway the link http://www.injektilo.com/LEDMATRIX/8...%20Example.JPG is just that in picture! Seems to be the best choice right now.

Ioannis

[mister_e]

seems to have a problem with the link

i think it could be http://www.injektilo.com/LEDMATRIX/8...%20Example.JPG

now let's show the schematic <IMG SRC="http://www.injektilo.com/LEDMATRIX/8%20Led%20Matrix%20Example.JPG">

[T.Jackson]

No, you cannot parallel LEDs Diodes or Bipolar transistors (only FET). Since each of them is not a resistor the current cannot be shared among them. You sure need a resistor in series.

Depends on the junction drop. If you have two LEDs perfectly matched, say 1.75V ea (or thereabouts) - both will share equal current. Tolerance levels are considerably quite remarkable nowadays. No need to spend hours with your meter looking for matched BJT pairs for that destined to be perfect amplifier.

[mekohler]

Thanks for the help guys.

I think I settled on constructing the matrix like this:


And the schematic is:



Let me know if you see any problems. Also, the book I am learning from recommended using the74LS174 decoder. and has provided example code.

[sayzer]

You seem to have good progress.

Here is a similar approach.

<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=2045&d=1190816000">

[Ioannis]

Depends on the junction drop. If you have two LEDs perfectly matched, say 1.75V ea (or thereabouts) - both will share equal current. Tolerance levels are considerably quite remarkable nowadays. No need to spend hours with your meter looking for matched BJT pairs for that destined to be perfect amplifier.

Sure technology advances forward but just to be sure, i'd put a small resistor there. You never know...

Ioannis

[T.Jackson]

<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=2046&stc=1&d=119088114 8" align="center" border="1">

Diagram above depicts two 1A power diodes paralleled together in attempts of obtaining 2A. As you can see, only a minor difference in drop (300mV in this case) - will mean that one of them is going to be working harder. In the case of what's illustrated above, D2 will be working around 5% more than D1.

If anyone doesn't agree with this, by all means speak up.
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