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Led Matrix 5x7 creation from scratch.

Discussion in 'Electronic Basics' started by Adrian de los Santos, Mar 6, 2004.

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  1. I guys, first sorry for my english.

    I am in a project where i need some 5x7 led matrix displays, but since
    it has been impossible for me to find such component here in mexico
    city, i want to create (or try to create) my own 5x7 led matrix, but
    here its where my doubts come, how the 5x7 led arrays works ? i have
    never use or seen one (appart form the photos on the web).

    Anyone has a schematic on how those things are build ?

    And more important, how they work ?

    I want to build something like this: (18mm) 5x7&Note=Dot Matrix&Tag=1


    Thanks a lot for your kind reply.
  2. Hard to believe you can't find such things in that great a town.

    Nevertheless, you can find most of the reply in the datasheets you
    mentioned. The LEDs are place in a 5x7 matrix, five columns, seven rows. All
    anodes of the LEDs in a column are tied together and all cathodes in each
    row are tied together. To light a particular LED you turn its column high
    keeping the others low and its row low keeping the others high. If you want
    to light more LEDs in that particular column, you pull their rows low XOR if
    you want to light more LEDs in that particular row, you push their columns
    high. You can't do both at the same time. To show a picture or a character
    you have to do either the rows or the columns one by one. If you're quick
    enough the eye will not see the switching just like a movie or a tv (or the
    PCs monitor.) Some hundreds of Herz up to about 1kHz are often used.

  3. Mikal Hadvik

    Mikal Hadvik Guest

    Anyone has a schematic on how those things are build ?

    Anodes tied to column pins, cathodes tied to row pins. LED at
    intersection of column pin driven high, with row pin driven low, emits

  4. Here its my problem, to tell you the truth i dont understand what you
    mean when you say keep the other low and high, someone told me that i
    need power in one side and a "open collector" on the other side, but i
    dont understand what its an open collector, and i have to appy current
    in both sides ? (columns and rows)
  5. "Open collector" generally refers to an IC having as its output an
    NPN transistor with its emitter grounded, and the collector connected
    to the output pin (with no other connection inside the chip)

    In these LED arrays, all the LEDs in a column have their anodes
    connected together, and all the LEDs in a row have their cathodes
    connected together.

    To light up one LED, you connect the appropriate column line to a
    positive supply, and the appropriate row line to ground (with a
    resistor somewhere to limit current, as with any LED.)

    In a normal application, you will pull column lines high, one at a
    time, while pulling row lines low as needed to light the appropriate

    Peter Bennett, VE7CEI
    peterbb (at)
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  6. Mikal Hodvik

    Mikal Hodvik Guest

    Whoa, there! You need resistors to limit LED current in this circuit! Put
    them in either (but not both) row or column lines. 150R gives about 20mA,
    which is the maximum continuous current for many discrete LEDs. Otherwise,
    your circuit should work just fine.

    When the display is driven by a multiplexed display driver, LED current can
    often be higher because duty cycle is low.

    Mikal Hodvik
    Decade Engineering
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