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LCD Help Please... — Parallax Forums

LCD Help Please...

idleupidleup Posts: 46
edited 2005-10-22 18:58 in BASIC Stamp
I finally got my LCD working but then I had to remove the stamp from the topboard in order to fix something. I then put it on backwards and noticed nothing worked. I then realized my mistake and put it on correctly but now the LCD doesnt work.

1. How can I diagnose if I fried the LCD?

2. Is there some diagnostic program that can test the stamps outputs to make sure none of them are fried?

3. Is there a way to protect the LCD from reverse polarity or other screwups? I imagine it only needs to be VSS and VDD that have this protection, maybe VBT which is 3.0v should be protected too. I have no idea how to do this.

Thanks,
Matt

Comments

  • NewzedNewzed Posts: 2,503
    edited 2005-10-22 16:23
    You need a Stamp Tester.

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    Sid Weaver
    Do you have a Stamp Tester yet?
    http://hometown.aol.com/newzed/index.html

    ·
  • idleupidleup Posts: 46
    edited 2005-10-22 16:31
    Okay, what about diagnosing and protecting the LCD?

    - Matt
  • dandreaedandreae Posts: 1,375
    edited 2005-10-22 17:07
    If you have a Parallax serial LCD you can test·it by setting the dip switches on the back to the test mode and see if it works.· As far as the stamp I/O pins you can use a LED and test each I/O by setting it high and see if the LED lights up.

    Dave

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    Dave Andreae

    Tech Support
    dandreae@parallax.com
    Http://www.parallax.com

    ·
  • JonathanJonathan Posts: 1,023
    edited 2005-10-22 17:45
    Matt,

    Most serial displays will perform a self test if the data line is grounded. Check the docs to see if that is true. However, since you inserted the Stamp backwards, I doubt if the LCD saw reversed voltages, so hopefully it should be OK. Try the LCD on other pins or another Stamp. Even if the i/o pin will light an LED there can be problems with serial comms, especially at higher speeds. I have seen this personally on a Stamp abused in class. Took a while to get it working.

    Jonathan

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    www.madlabs.info - Home of the Hydrogen Fuel Cell Robot
  • JonathanJonathan Posts: 1,023
    edited 2005-10-22 17:47
    I forgot...

    A hefty diode on the power supply to the LCD will protect it for a while until it blows. A better way is to limit the current to the LCD with a resistor of the correct value to allow the LCD to function, then select a diode that can handle that current indefintley.

    Jonathan

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    www.madlabs.info - Home of the Hydrogen Fuel Cell Robot
  • idleupidleup Posts: 46
    edited 2005-10-22 18:13
    It is not a serial LCD. It is an One Stop Displays HD47780 Compatible LCD. I guess that it wouldnt matter what kind of LCD it is to do the suggesitons with the resistor and diodes.

    Jonathan, regarding your comment on limiting the current, I thought it would only draw the current it needed regardless of what the supply current is?

    - Matt
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-10-22 18:16
    Matt,

    ·· That is true...The LCD will draw only the current it needs.· If this unit is not backlit, it should be 10mA or less.· In any event, if something's connected wrong/backwards the current it "needs" can go up significantly, toasting something.· By the way, it isn't clear from your first post whether you put the Stamp Module in backwards or the LCD?

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • idleupidleup Posts: 46
    edited 2005-10-22 18:25
    I put the stamp module in backwards. It is actually an OWL logic board that I placed in a topboard backwards. The LCD specs show the LCD pulls 100mA.

    I put the PDF spec on the LCD in one of my prior post but cannot find it. The Part is OSD2002BYPNJB

    - Matt
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-10-22 18:27
    Isn't it possible that the Stamp Module is damaged, and not the LCD?· The LCD won't do anything (Usually) unless it receives commands from the Stamp Module.· So are you sure the Stamp Module works?

    Also, is this thread related to: http://forums.parallax.com/showthread.php?p=553896

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com


    Post Edited (Chris Savage (Parallax)) : 10/22/2005 6:44:02 PM GMT
  • idleupidleup Posts: 46
    edited 2005-10-22 18:58
    I just tested the stamp using the method you suggested. Everything is okay, and all pins are working. The problem must be in the LCD. Do you have any suggestions on how to diagnose that?
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