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Author Topic: Is my 8x8 display broken or am I doing this wrong  (Read 358 times)
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I have was using the 8x8 LED display (1588BS) that came with my starter kit (not the official starter kit from Arduino mind you) and I had it a set up with two 595 shift registers and got some pretty funky results.  I had difficulty finding a datasheet and checking the forums I noticed that others did too.  So I decided to set up a simple rig (shown below) and test to see if the datasheet (shown below) was accurate, here are the results of my test (also shown below).  I have done multiplexing projects with shift registers before but am still new enough to this that I am not sure if the datasheet is wrong, I am rigging it wrong, or if the hardware is just faulty.  I am leaning towards faulty hardware at this point but really just want someone to confirm this and tell me I'm not crazy.
Thanks,
Josh









I am also not real sure how to post photos, so I attached everything in a PDF file as well

* 8x8LED test.pdf (1968.63 KB - downloaded 18 times.)
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Sorry, I just realized I posted this to the wrong place, but it won't let me delete it.
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Sorry, I just realized I posted this to the wrong place, but it won't let me delete it.
No it's the right place as this is an LED matrix not a display.

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and got some pretty funky results
Not very scientific, nor useful in conveying to others what is going on.

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I am rigging it wrong
No idea as you haven't told us how you are rigging it.
You need to post a schematic ( a real one not a fritzing abortion ) and you need to post your test code and say what it does and what you want it to do.
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Let me try again,
Because I was getting "funky results", I took it apart and tested each row pin and each column pin one by one; not connected to the arduino and no test code (which is why I believe I posted this to the wrong place).  The "fritzing abortion" I posted are the results of which LEDs light up when taking the row and column pins high and low respectively one by one, I believe the results show that the 8x8 matrix is faulty, but would like someone to confirm this.

Again, because it is not connected to the Arduino at all I don't think this is the right forum for this question.  I also should have known to lable the post 8x8 matrix instead of display, apologies for the stupid mistake.
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Hi, this link shows how the 8x8 red LED array is assembled to a driver PCB.
If you look at the pic with the PCB completely disassembled you will see on the PCB screen which pin is number 1, the display plugs into the PCB the way it is placed next to it, with the part number and dimple to that side.
I have one of these arrays, I got it right by plugging it in the wrong way first, didn't damage anything because of diode junctions.

https://www.flickr.com/photos/andrew-d/8062491580/in/photostream/

Hope it helps.

Tom...... smiley
« Last Edit: May 05, 2014, 08:05:38 am by TomGeorge » Logged

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The "fritzing abortion" I posted
No you didn't do anything of the sort.
Looking at those results they look odd, do make sure you have identified the pins correctly. If the pins are correct I can not think of any fault you could have that would produce those results, so it is unlikely to be a faulty display.
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With just 1 pin high and 1 pin low, there is no way to have multiple LEDs turn on.
Your testing looks to me like you have the part at the lower right of the datasheet,
where you applied a High (resistor & red wire) to a common anode pin and then walked a low (white wire) across the discrete cathode.
There must  be some weak connections between the cathode pins to make them light up like that.
What value was the resistor?
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It strikes me looking at the photograph that you have no way to access the top row of connectors with your probes. Is this exactly how you wired it? Moving it down a row would be better.

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What value was the resistor?
Looks like a 2K2 from the photo in the attachment.
« Last Edit: May 05, 2014, 11:49:07 am by Grumpy_Mike » Logged

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Sorry for the delayed reply, just got home from the night shift
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What value was the resistor?
It's a 1k, the picture is a little fuzzy but I just grabbed 1k since I was only testing the LEDs for a brief period.
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It strikes me looking at the photograph that you have no way to access the top row of connectors with your probes. Is this exactly how you wired it? Moving it down a row would be better.
The picture is a little off angle, but as it sits there are three rows of access to the bottom pins (C D and E of the lower bread board), and two rows of access to the top pins (F and G of the upper bread board). I could move it down a row but it would just mean two rows of access to the bottom pins, and three rows of access to the top pins.
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With just 1 pin high and 1 pin low, there is no way to have multiple LEDs turn on.
That's what I was thinking too, but I was getting several lit LEDs (of varying brightness) with just one  pin high and one pin low.  So you think that does mean there are some weak connections within the matrix itself?  Nothing to do but get a new matrix?

Heading off to dreamland, will check back in later in the day.
Thanks for all the help everyone has already offered! smiley
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