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Read Input to a Matrix LED Display

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ZebraTJ

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I am trying to interface a device to a PDA (Palm OS). This device does not have an external interface but it does display its output to an 8 character 5x7 matrix LED display. The display is connected to the main board by 6 connections. My idea was that I could read the data being sent to the display as the output of the device. There are part numbers on the display but I don't have them right now and I don't know if they would help or not. Will this approach work? How complex of a circuit will I need to read the display input and write it to the PDA's serial interface? Will I need an oscilloscope to try to determine which input lines to the led do what function? Thanks for any input!
 

crust

Member
It might be possible, but it will take some work. The matrix display is scanned meaning that one column or one row is illuminated at a time very rapidly so that the persistence in your brain makes one coherent picture. What you would need to do was tap into the first scan and use that to tell your device where the start of frame is. then you can use a circuit to conver the matrix into 1/0 for input to your device.
 

ZebraTJ

New Member
I was thinking the inputs to the LED device are inputs to a controller chip which is contained in it and therefore the inputs are digital signals. I thought maybe one input was a clock, another data, etc. and the processor of the main device was sending commands and data to it. Does that sound possible?
 

crust

Member
I suppose there might be some "smart" LED matrices available, but I have never seen or heard of a device (though I have never explicitly looked for such a part). I have several made by Liteon and Kingbright that are the matrix type.
 

ZebraTJ

New Member
The 8 LED matrices are packaged into a single component that has 6 connections going to it so doesn't that mean there has to be a controller in the component? I've been researching and am hoping that it talks I2C. I think one input is ground, one is reference voltage, two more are maybe for brightness control or ??, and the other two are the I2C lines. To investigage further I think I need a scope to monitor the lines?
 

ZebraTJ

New Member
If the LED component, which is a bank of (8) 5x7 LED's enclosed in what looks like solid plastic, did not have a controller wouldn't it have to have one input line for each LED (8x5x7=280) so each one could be on or off?
 

crust

Member
If there is only 6 pins then it probably does have something in it that makes it go. To answer your question, a 5x7 matrix will have 12 wires usually and you can turn leds on/off by sourcing and sinking from different pins. In your case, you have 8 of these end-to-end. Perhaps there is a bank of shift registers along the bottom edge that will sink the current from each column and a ahift register on the edge to activate each row. In that case, it would need a clock. Do you have a part number or photo of the device you can post?
 

ZebraTJ

New Member
Here are some photos. They are a little blury. The square IC behind the led component has Samsung and 3P8475 0ZR5 on it and one pin visibly connected to the led. The led has SCE 8754 OSRAM 0214 on it. Does this help? Is using a scope the next step to determine the communication?
 

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crust

Member
I cant read the part numbers, but there are some smarts on the board. Those appear to be GALs or PALs or perhaps something else. The easiest way to get it working would be first to see if there are any labels anywhere on the signals, maybe at the chips, perhaps at the header. Figure out where power and ground are (those are easy to ring out from the chips), then you can just start trying different things to see if you can get anything to happen. Perhaps assume one is a clock, hold the others high, see what happens. Depending on what you find, you might need a scope or analyzer to figure out what is going on. Alternatively, see if you can read off some of the part numbers from the chips.
 

ZebraTJ

New Member
This was in my last post but maybe you didn't see it at the top. The square IC behind the led component has Samsung and 3P8475 0ZR5 on it and one pin visibly connected to the led. The led has SCE 8754 OSRAM 0214 on it. Does this help?
 

crust

Member
ZebraTJ,

I was working on a circuit earlier and just by chance stumbled across a site which seems to have a display that at least physically resembles yours. They refer to it as an HDSP-2000, the site is [here. You have to scroll down a bit to spot it. If in fact it is the same, they link to an application note that perhaps indicates how to program it.
 
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