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Parallax serial LCD weirdness — Parallax Forums

Parallax serial LCD weirdness

Don FrenchDon French Posts: 126
edited 2007-06-07 14:56 in General Discussion
I have two serial LCDs, a 2x16 and a 4x20. Both of them worked fine at first. , but now I have trouble with both of them. I can start up a Javelin on a demo board that is connected to a LCD and most of the time the display shows nothing but the cursor. Sometimes it displays a partial string, losing the beginning of the string. Power down and power up without touching a thing and the display that has been displaying only a cursor works fine for the entire time I have the power on. I am not doing anything different between runs so I can't figure out what is causing it to work some of the time and not others. I am now using the 4x20 but I had the same experience with the 2 x 16. When they were new, both of them worked perfectly all the time. Then they got flaky. If it weren't for the fact that sometimes it starts up fine and stays working fine until the next power off/on sequence, I would say that the LCD is just going south on me. I don't understand how to explain this behavior? Any ideas?

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2007-06-06 03:22
    Don,

    I have never seen this behavior before in one of these displays. Sounds like a bad/intermittent connection maybe?· Perhaps something in the DIP switch causing it to have the wrong baud mode after what you described.

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    Chris Savage
    Parallax Tech Support
  • Don FrenchDon French Posts: 126
    edited 2007-06-06 03:51
    The DIP switch is right, as demonstrated by the fact that it works flawlessly one time and I power down and back up and it fails the next without me touching a thing or changing a line of code. That is the weird thing. But maybe there is a flaky connection, as you say. I am going to systematically work through everything tomorrow and see if I can't stomp this bug to death.
  • Bruce BatesBruce Bates Posts: 3,045
    edited 2007-06-06 05:22
    Don -

    Do you happen to have another LCD around that you could use temporarily? If so, that might eliminate or confirm a faulty LCD immediately.

    Regards,

    Bruce Bates

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  • ghost13ghost13 Posts: 133
    edited 2007-06-06 07:57
    I have that same problem with my new LCD (from 2x16 Backlit Serial Parallax). Sometimes the text is displayed halfway across the screen (as in it starts there). This only happened about 2 times, but it happened...
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2007-06-06 15:39
    Gentlemen,

    It occurs to me that if you don’t have the proper initialization you can get these same symptoms…There is a HIGH command for the LCD line, followed by a PAUSE. These should be in your code at the beginning. Also, if you use the CLS command you must use a PAUSE 5 after. In each case I can recall weirdness at startup that was the issue. Of course, in those cases it was only during startup. After that everything displayed correctly, although the cursor mode sometimes hadn’t been set properly.

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    Chris Savage
    Parallax Tech Support
  • Don FrenchDon French Posts: 126
    edited 2007-06-06 17:42
    I am using a Javelin Stamp and my code does a CPU.writePin(LCDpin, true) followed by a CPU.delay(10000) on startup. Actually, I tried writing false and doing nothing just to see if it made a difference and it did not. I am not at home right now and I don't remember if there is a CLS or not. But I am sure that if there is that I do not follow it with a delay, as I think I missed that point in the data sheet. Still, since no subsequent output appears, I don't think that is the problem. Probably a flaky connection, as Chris suggested. Tonight when I get home I will try to nail it down.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2007-06-06 17:54
    Don,

    Do you happen to have a BASIC Stamp? It would be interesting to see (since you’re using a Javelin) if this happens on a BASIC Stamp just to help narrow down the issue.

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    Chris Savage
    Parallax Tech Support
  • Don FrenchDon French Posts: 126
    edited 2007-06-06 18:03
    Yes, I do have a BASIC Stamp. I can try that tonight as well.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2007-06-06 19:04
    Try it with our demo code and see what happens. Take care.

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    Chris Savage
    Parallax Tech Support
  • Don FrenchDon French Posts: 126
    edited 2007-06-07 04:25
    It works fine on the BASIC stamp. I couldn't get it to work on the Javelin though and in the process of working on the problem I apparently fried the Javelin (it's a long story). I am getting another Javelin tomorrow and will mush on. I am pretty sure that there is no problem with the LCD at this point though.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2007-06-07 14:56
    Don,

    That’s good news…Sort of…Definitely when things start getting weird I usually try to narrow the problem down by replacing components on both sides of the equation. In this case the controller. Remember, you can get a discounted replacement on a damaged module by contacting us at Parallax. Take care.

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    Chris Savage
    Parallax Tech Support
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