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Dot matrix display

Discussion in 'Electronic Basics' started by Roger Dewhurst, Mar 18, 2007.

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  1. I have been given a number of 7x5 dot matrix display segments. There are 7
    pins at the top and 7 at the bottom. The ID on the segment is:

    LTP2157AE
    927 TAIWAN P

    Can someone be kind enough to explain the pin-out for me.

    R
     
  2. BobG

    BobG Guest

    Try an ohmmeter on diode test setting both ways.... could be common
    anode or common cathode
     
  3. Chris

    Chris Guest

    Hi, Roger. Can't find the part -- I'd guess you might have to get out
    your DMM and use the diode tester.

    Here's a standard pinout that might help:

    http://www.lumex.com/images/pdf/LDM-21257NI.pdf

    ood luck
    Chris
     
  4. Thanks. This looks like an identical device!

    Roger
     
  5. I have printed out the document but how do I work out what the pins do.

    I can see that there are 8 anode pins and 6 cathode pins but that is about
    as far as I get.

    R
     
  6. Randy Day

    Randy Day Guest

    Roger Dewhurst wrote:

    [snip]
    Connect 3 to 5 volts (through a current-limiting
    resistor), negative to one cathode, positive to
    each anode in turn; each time a different spot
    should come on. Move neg. to the next cathode,
    then pos. to each anode again - different spots
    come on.

    R
    |-----/\/\/\--- cathode
    -
    --- 3-5VDC
    |-------------- anode

    Choose the resistor value to limit current to
    25mA. As the small schematic in the doc with all
    the diodes shows, they're arranged in a row-col
    matrix.
     
  7. Chris

    Chris Guest

    Hi, Roger. Driving the displays you have might not be the easiest
    thing for a newbie. They work on the time multiplexing principle. If
    you apply 7 bits of data to the anode pins, and then activate one of
    the cathode pins, one row of the diplay will light. By using a
    computer or microcontroller amd appropriate high current latching
    drivers, you can scroll across the rows at a fast rate (say, 1000
    times a second or so), and due to persistence of vision it will appear
    that all the rows are on at once. A typical microcontroller can
    easily handle this and also take care of other things such as
    maintaining a communications link and taking care of other business.

    But unless you've got that microcontroller, it is going to be really
    difficult to get a whole lot of use out of your display.

    Good luck
    Chris
     
  8. Thanks. I just wanted to use them to display a time in milliseconds between
    two events. Since I got a bunch of these 7x5 LED matrix devices I thought
    that I might try and use them. Obviously there are easier ways.

    Roger
     
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