Possible causes for multiple serial 2x16 lcd failures after only 2 week use
sport270
Posts: 82
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
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?
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.
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.
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.
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The Serial LCDs are actually less prone to wiring problems than the Parallel LCDs.
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.