How to identify the pins of a 4 line LCD display

Discussion in 'General Electronics Chat' started by davebee, Feb 28, 2013.

  1. davebee

    Thread Starter Well-Known Member

    Oct 22, 2008
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    I have a standard 4 line 40 character LCD unit which has a two-inch ribbon cable that ends in a 16 pin socket of 2 rows of 8.

    The data sheet has pinout charts showing that pin 1 is D7, pin 2 is D6, pin 13 is ground, 14 is +5, etc.

    But looking at the end of the socket, which is pin 1? There are 4 possibilities, but I don't have a clue which is right.

    There are no markings on the socket; it's just a generic ribbon cable with press-on connectors.

    I've searched dozens of data sheets, and they all tell how to do everything you could ever want with this display, except how to identify the pins on the connector.

    Can anyone help?
     
  2. t06afre

    AAC Fanatic!

    May 11, 2009
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    Can you post a link to the datasheet
     
  3. takao21203

    Distinguished Member

    Apr 28, 2012
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    If you have the datasheet for any of the ICs, you can test with a DMM for Vcc/GND. As well if there are any buffer capacitors (large), you can do the same here.
     
  4. davebee

    Thread Starter Well-Known Member

    Oct 22, 2008
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    I had been looking at generic HD44780 datasheets but that weren't for this exact unit.

    But I may have found the exact datasheet. It looks like "nan ya plastics" made it:

    http://www.mark-products.com/pdf/c40x4/028/028 spec.pdf
    http://www.mark-products.com/pdf/c40x4/028/028 dwg.pdf

    These give the pin config for the board itself, but not that little ribbon cable, but it's a start. I just need to figure out which side of the end of the ribbon connector is pin 1.

    There are no large capacitors at all on the board; just little surface mount ones.

    On the unit that I have, the ribbon cable is soldered to the LCD board, so I'm worried about a continuity tester sending the wrong polarity of voltage onto some sensitive pin. I wonder if I make my own low voltage continuity tester with like half a volt thru a large resistor, if that could probe the continuity without damaging anything.
     
  5. takao21203

    Distinguished Member

    Apr 28, 2012
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    A DMM continuity tester won't damage anything.

    Normally the order for these Hitachi LCDs is pretty standard. If there are extra pins they are added on the highest order.

    the yellow component on the right to me looks like a Tantalum storage capacitor, hard to say from the photo.

    So the cable isn't detachable?
     
  6. t06afre

    AAC Fanatic!

    May 11, 2009
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    If you zoom up the connector side in the 028%20dwg.pdf file you will some numbers. One row has the odd numered pins. And the orther row has the even numberd pins. You may also see some markings on the top side
     
  7. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    The spec.pdf shows pin functions.
    The dwg.pdf shows pin locations.

    I believe those connectors don't invert, mirror, swap, or change the wiring locations, so the drive end should be the same physical layout as the display. You can (should) check this with an ohmmeter, or visually by looking at the backside slots that indicate where the wires connect to pins.
     
  8. davebee

    Thread Starter Well-Known Member

    Oct 22, 2008
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    I had an idea. Since the spec pdf shows the voltages for the board pins, all I should need to do is apply +5 and ground to the correct board pins, then test which cable-end socket hole shows the +5 volts. That should be enough to lay out all the cable-end connector pin assignments.

    Of course, actually getting the display to work is the real test; that'll come tonight, I hope.

    Thanks to everyone who responded.
     
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