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Hi,

I'd like to create a led panel like this one: http://www.nerdkits.com/videos/ledarray2/

For now I only have two columns with 5 rows so 20 LEDS (5 LEDS per column * 2 columns * 2 LED columns per column). I am having trouble when trying to light up only one led at a time. I turn all output pins to LOW and set the related row pin to HIGH so that current will be able to flow. The problem is the following:

Given the fact the 2 columns are setup exactly the same way, the same led on the same row of those 2 columns will lit up... This is why I am trying to set one of the two column pins as an LOW INPUT but this does not help.

Here is the code for clarity:

              for (int i = 0; i < ROWS_NUMBER ;i ++){
                digitalWrite(ROWS_PINS, LOW);
              }
              
              for (int i = 0; i < COLUMNS_PINS_NUMBER ;i ++){
                  digitalWrite(COLUMNS_PINS, LOW);
              }
                
                  digitalWrite(ROWS_PINS[1], HIGH);
                 pinMode(COLUMNS_PINS[1],INPUT);
                  digitalWrite(COLUMNS_PINS[1],LOW);

How can I make it so that only one led at a time is lit on?
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Set all pins as INPUTs, then set only the relevant row and column lines as OUTPUT and HIGH and LOW as required.
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Only put one column high, the other low. Then put only one row high and the others low.
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Only put one column high, the other low. Then put only one row high and the others low.

That assumes the max reverse voltage rating for the LEDs is 5V or more (usually the case), my method doesn't assume that though.
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"Set all pins as INPUTs, then set only the relevant row and column lines as OUTPUT and HIGH and LOW as required."

This is what I do but as I said, but the leds mapped on the column I set as INPUT light up anyway.

"Only put one column high, the other low. Then put only one row high and the others low."

This is also what I've been doing, but the thing is that it works only if you have one column because the patterns then repeats over x columns.
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Maybe you should clarify the wiring of the LEDs for us?
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Yes fewe what you report can not happen if it is wired up correctly, so a schematic and a photo would be good.
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The schematics is on the website: http://www.nerdkits.com/videos/ledarray2/mikeyplex.png

I tried to put a 10k resistor but it didn't really help.
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Where are the resistors! You need about 270R in line with each column.
You never said this was a charleyplexing circuit, you drive those very differently from a normal matrix.
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Hello Community,

Simple Outdoor LED Message Moving or Scrolling Sign Board Design Project with Circuit diagram Electronic LED Scroller Generator for outdoor digital signs Marketable LED sign board with Message scrolling. LED Message Scrolling Board with completed circuit diagram and the micro controller programming. Sometimes this LED scrolling message board is referred as LED Message sign board.

Generally the LED Scroller Message Generator can be implemented with many different logic. Out of two are very famous

1. LED moving message display board design using decade counters.

2. LED moving message display board design using shift registers.

The second one is very simple for a beginner. So, this post I am implementing LED moving display using shift registers. LED Scrolling Display can be implemented by using any micro controller like 8051, PIC and AVR controllers. Here, I implemented Scrolling Display by using 8051 microcontroller i.e. 89s52 microcontroller. The next post will show the implementation by using PIC and AVR micro controllers.

Thanks and Regards,
Anthony Martello  smiley
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Where are the resistors! You need about 270R in line with each column.
You never said this was a charleyplexing circuit, you drive those very differently from a normal matrix.

I'll try that but I tried putting 10k resistors on each column to be sure but it didn't so AFAIK a 270R will give the same result.

BTW sorry for the delayed answer
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Quote
but I tried putting 10k resistors on each column
That will give you 0.5mA to share between all the LEDs I would be surprised if you can see anything with that.
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