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Possible causes for multiple serial 2x16 lcd failures after only 2 week use — Parallax Forums

Possible causes for multiple serial 2x16 lcd failures after only 2 week use

sport270sport270 Posts: 82
edited 2014-11-24 09:20 in BASIC Stamp
need possible causes for 2x16 backlit serial lcd screen to display solid black pixels on right half of the screen character boxes. Another started displaying random code or Symbols instead of the programmed digits. The failures have been after 2 -3 weeks o use

Comments

  • LeonLeon Posts: 7,620
    edited 2014-11-23 06:57
    Which LCD displays are they?
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2014-11-23 07:20
    These are certainly unusual failures. I have fried several LCD with reverse polarity and always go all the character blocks to turn completely black. Over-voltage and reverse polarity will cause instant damage that is beyond repair.

    We do need to know if these are or are not Parallax products, or come from another source. Many of use have experienced oddball failures from buying to lowest priced sources on EBay and it seems that defective units that appear cosmetically okay manage to end up there.

    What is the remedy? Well, a broken or defective LCD usually is beyond repair. Early failures usually imply asking the vendor for a free replacement.

    Are you running a standard proven test code, or is it possible that your code in generating these behaviors?
    Are you running a 5VDC device with 3.3VDC logic and no pull-up resistors?

    Are you running on a low battery? (A backlit LCD will run down a battery very quickly)
    Are you sure your code to initialize the LCD runs completely and correctly?
  • sport270sport270 Posts: 82
    edited 2014-11-23 07:48
    Parallax PN# 27977 from Mouser Electronics....The latest failure started out with my error in connecting the LM7805 to the VDD +5 pin # 21 on the bs2 & also to the lcd.... It would shutoff the screen after approx 10-15 min, then come back on after you powered down. I then seperated the bs2 from the LM7805, and allowed the LM7805 to run only the lcd. I connected LM7812 to tyhe VIN pin 24 on bs2 . Shortly therafter, the lcd displayed bunch of %&< or garbage instead of the normal numeric values. Then stopped coming on at all. The first failure was without issue in beginning, running for weeks, then it displayed bunch of black pixels on entire character blocks of right side of screen only, then it stopped working aswell. Also the only other thing i did with the last one was connect the 3 pins to leds that were going through 1K resisters to leds then other side of led's were grounded. Bs2 controlled led's when going high... and also one output went through 1k resister to the gate of a Tip120 that was tied to piezo buzzer.
  • sport270sport270 Posts: 82
    edited 2014-11-23 07:49
    might add that these few are the only ones i have done, and all resulted in failure... :(
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2014-11-23 07:56
    The Forums can only help with either the wiring problems or software problems.
    If you want Parallax to accept a return of defective merchandise, you need to contact the Customer Service.

    Reverse polarity and over-voltage must be avoided at all costs with the LCDs. They are very unforgiving of either of these mistakes.
  • NWCCTVNWCCTV Posts: 3,629
    edited 2014-11-23 16:27
    Another started displaying random code or Symbols instead of the programmed digits. The failures have been after 2 -3 weeks o use
    In my past experiences this has been caused by using the incorrect Baud rate.
  • sport270sport270 Posts: 82
    edited 2014-11-23 18:29
    Can anyone give me any pointers or lessons learned from these serial lcd's.....? Any known issues
  • GenetixGenetix Posts: 1,754
    edited 2014-11-23 18:52
    Stick to one of Parallax's Stamp boards if you can. If you are going to wire up your own power supplies then post your schematics first so other can check them. Then double and triple check your wiring. Better yet stick to batteries. 4AA batteries through a diode such as a 1N400x should be safe enough for most 5V devices. If you need more current though then use Cs or Ds.

    Now would be a good time to get a board from Parallax since everything is 20% off if you use the code you see at the top of the screen. The Homework board has built in 220 ohm resistors that protect the I/O pins but the Board of Education is the most versatile. Unfortunately Parallax no longer carries the Professional Developer Board but you can still get it online.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2014-11-24 06:14
    Parallax has Documents and Sample Code to download for free

    http://www.parallax.com/product/27977

    I am very unsure that your devices have suffered any real damage.

    You might have suffered a shut down of the BS voltage regulator due to demanding too much load in your first configuration. The voltage regulator will simply shut off until it cools down and then work normally.

    If you don't understand BAUD rate and serial formats, you will get the LCD to display junk (and you seem to have junk).

    As I said in my first posting, the normal failure behavior is to have all 32 character spaces provide a full black block. This will appear without any communications connected. The device would be completely unresponsive to input.

    ++++++++++++
    The Serial LCDs are actually less prone to wiring problems than the Parallel LCDs.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2014-11-24 09:20
    The rare failures I have seen have been related to either environmental issues (elements getting into the display/board in machines) or switching the LCD on/off via a FET while the controller is still powered without taking precautions.

    So in the first scenario I have seen a few that were exposed to environmental conditions they were not designed to withstand. In the second the LCD was switched on/off via a FET to reduce power consumption, however the I/O pin connected from the MCU to the input of the LCD was still active. This can damage the controller on the backpack. Usually this results in it simply not responding to input, however it is possible for it to cause more damage.

    Usually when I hear the word garbage being used to describe what is being displayed it is because of a baud rate issue. On the LCD this could be cause by something happening to the little DIP switches on the back that set the baud rate. One thing you can try is to see if the demo mode still works. I have also sent the module data at all three supported baud rates to see if a switch was bad. If it works at the "wrong" baud rate then one of the switches is bad and it is in a different speed than what you think. Note that you must cycle power to the display after changing the DIP switch settings.
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