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2x16 Serial LCD burning out — Parallax Forums

2x16 Serial LCD burning out

dexxteritydexxterity Posts: 14
edited 2013-09-25 21:01 in General Discussion
I keep burning out the Parallax 2x16 LCD display and before I plug my third one in I thought I'd save myself some money and come here to find what I am doing wrong.

My set up is as follows: I have the I/O pin going directly to a pin on the Parallax Protoboard and I am powering the screen with the 5v pin that comes off the protoboard. I have used a voltage meter to confirm that it is indeed a 5v pin.

What am I missing here?
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Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2013-09-08 20:14
    Somehow you're not connecting the display to the places you think you are using. You can't burn out this display by wiring the ground lead of the display to the ground of the Protoboard and the +5V power lead of the display to the +5V supply of the Protoboard and the I/O line of the display to an I/O pin of the Protoboard, so you must be wiring one or another leads to something else. Remember that the servo sockets can have one of two voltages on them, either +5V or Vin. If you have the jumper set to Vin, that can burn out the display if it's plugged into one of the servo sockets.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2013-09-08 21:14
    Are you trying to use backlighting from the +5VDC?

    I suspect that perhaps backlighting only wants 4.2VDC and you have not provided a current limiting resistor to bring the +5.0VDC down to that. This is a detail that is often missed. Read the LCD specification sheet carefully.

    If you don't use backlighting, the LCD should work fine with +5VDC power to logic.

    On the other hand, if you accidentally wire reverse polarity at any time, it is sudden and complete death to an LCD. Over-voltage via Vin is also a source of damage as Mike G. mentions above.
  • RDL2004RDL2004 Posts: 2,554
    edited 2013-09-08 22:18
    The Parallax LCDs only have 3 connections, +5v, ground, and RX (data). If it's one that has a backlight, that's taken care of by the board.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2013-09-08 23:49
    Yes, serial LCDs properly take care of backlighting, and apparently Parallax only sells parallel LCDs without. So the backlighting is not an issue.

    So it would seem to be an over-voltage failure or reversed polarity are the two hazards.
  • Ron CzapalaRon Czapala Posts: 2,418
    edited 2013-09-09 05:09
    The manual warns "Do not provide a signal to the 'RX' pin before applying 5 VDC to the '5V' pin"

    If you do not have power supplied properly, it sounds like you can damage it.
  • skylightskylight Posts: 1,915
    edited 2013-09-09 05:12
    have you tried switching to demo mode to see whether the LCD is still ok ?
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2013-09-09 09:29
    I would be curious to see a photo showing your connections to help ensure you're connecting to the correct places. Can you take a photo of one that was connected and damaged?
  • dexxteritydexxterity Posts: 14
    edited 2013-09-14 21:13
    Here are some pictures:
    image.jpg
    image1.jpg
    image2.jpg
    photo.jpg
    image.jpg
    1024 x 765 - 141K
    image1.jpg
    1024 x 765 - 157K
    image2.jpg
    1024 x 765 - 138K
    photo.jpg
    1024 x 765 - 130K
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2013-09-16 08:38
    Okay, looking at your connections, if the white wire is connected to P6 then it seems everything is good with these connections. Assuming these are being damaged on the same board the only thing I can think of is possibly noise on the 5V supply. This wouldn't show up with your meter (you'd need a scope to see it), and it shouldn't affect the 3.3V supply which has its own regulator and filter caps. But a bad cap or regulator on the 5V side could be causing noise/oscillations. Just out of curiosity is anything else connected to the 5V supply besides the LCD?
  • dexxteritydexxterity Posts: 14
    edited 2013-09-16 09:33
    Yes also connected to 5V is a HID RFID module. Is there a way to reduce noise? Unfortunately I do not have an oscilloscope to confirm or deny its presence.
  • T ChapT Chap Posts: 4,223
    edited 2013-09-16 12:30
    What is the symptom? If this is the backlit version, is the backlight on or not on power up? If it does light up, are you just not getting a response when you should be on the screen?
  • dexxteritydexxterity Posts: 14
    edited 2013-09-16 15:30
    The symptom is the display will not display text (even in demo mode). Also when power is applied to it the piezo emits a flickery glitch noise. Some more info about how it happened - the display worked fine for about 30 minutes. It displayed text I sent to it and it exhibited no symptoms. After that it stopped displaying text and started making the chirping noise.
  • T ChapT Chap Posts: 4,223
    edited 2013-09-16 16:51
    You mean both have identical symptoms?
  • skylightskylight Posts: 1,915
    edited 2013-09-17 08:00
    Are you sure you have 5v DC could it be rippling or even AC?
  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2013-09-18 16:16
    One Very crafty way to Hear AC noise on a LOW VOLTAGE! DC bus is a speaker and a 10 UF or so cap ....

    use the cap in series with the speaker to block the DC and it will pass the AC on to the speaker ...

    used this old trick to find a tach lead on a car in the middle of a Iowa winter to install a remote start kit .


    WARNING can LOAD up a circuit !!!!! use with care .......
  • T ChapT Chap Posts: 4,223
    edited 2013-09-18 17:32
    The 2x16 Backlit version is fickled, I have had about 10 go bad. Today, a brand new one doing crazy beeping, weird stuff on the display.
  • ercoerco Posts: 20,256
    edited 2013-09-18 19:55
    @T Chap: You've had TEN LCDs go bad?

    Sounds like I better try one of mine out before I stash them away!
  • T ChapT Chap Posts: 4,223
    edited 2013-09-18 20:08
    Yes, about 10 out of 150.
  • RDL2004RDL2004 Posts: 2,554
    edited 2013-09-19 05:44
    From Parallax?
  • T ChapT Chap Posts: 4,223
    edited 2013-09-19 06:54
    Yes, I use a lot of the 2x16 Backlit Parallax LCD.

    Yesterday a brand new one didn't work, it was putting crazy stuff on the screen when set to 19200(what I need), beeping crazy stuff when it received input. I set it to Test mode and it worked. I put switch 1 to ON and the Test mode still worked. I put 1 to OFF, 2 to ON, and the test did not work. So I traced out switch 1 to the Atmel on the PCB, and the pin stayed at 5V no matter where the switch 1 was located. However switch 2 was changing it's pin state. I need 19200, so I just ran a wire from the pin connected to switch 1 and took it to ground and now this one is working. Others have had different problems, bad pixels, no response, etc.

    For the OP, try this:

    Power off
    both switches to OFF
    Power on>see if Test works

    Power off
    set Switch 1 to ON, 2 to Off
    Power on>see if Test is still working

    Power off
    set switch 2 to on, 1 to Off
    Power on>see if Test is still working
  • Mike GreenMike Green Posts: 23,101
    edited 2013-09-19 07:07
    It sure sounds like an overvoltage problem with the +5V supply, maybe from noise or oscillation, stressing the LCD controller until it fails, but it could be a supplier problem. With that number of failures, you should call Parallax Tech Support. This is not something that's going to get resolved via the forum.
  • Ron CzapalaRon Czapala Posts: 2,418
    edited 2013-09-19 08:08
    Mike Green wrote: »
    It sure sounds like an overvoltage problem with the +5V supply, maybe from noise or oscillation, stressing the LCD controller until it fails, but it could be a supplier problem. With that number of failures, you should call Parallax Tech Support. This is not something that's going to get resolved via the forum.

    As I mentioned earlier in the thread, the product guide warns against sending data unless 5V is applied.
    I assume that if there is a loose connection on the power pin, it could cause a problem. Maybe Parallax could explain the consequences of doing so.

    Also the Stamp examples raise the RX pin high and pause to allow initialization to occur.
    CAUTION


    DO NOT PROVIDE A SIGNAL TO THE 'RX' PIN BEFORE APPLYING 5 VDC TO THE '5V' PIN.

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2013-09-19 08:51
    As I mentioned earlier, I suspect the 5V supply on the board. With wires solder to both sides of the Tantalum cap on the 5V supply there is the possibility something is happening on the 5V side. I would have tried the new LCD Modules on a new board before plugging them into the problematic one. That would certainly narrow things down. Then if you connected it to the original board and it failed, you'd know. I would also consider sending the board in for testing.
  • ercoerco Posts: 20,256
    edited 2013-09-20 10:19
    Ron Czapala wrote: »
    As I mentioned earlier in the thread, the product guide warns against sending data unless 5V is applied.
    I assume that if there is a loose connection on the power pin, it could cause a problem. Maybe Parallax could explain the consequences of doing so.

    Also the Stamp examples raise the RX pin high and pause to allow initialization to occur.

    Would also like to hear more about this from Parallax. Is sending data before applying 5V a bigger no-no than "crossing the streams"? I'll have to play with my pile of new Shack LCDs on Saturday.
  • ercoerco Posts: 20,256
    edited 2013-09-21 00:18
    Very nice module, the Shack 27977 RT unit. Played around for an hour tonight with a BS2, no problemo. POST works fine, tried that a dozen times. Started with sample code from http://www.parallax.com/sites/default/files/downloads/27979-Parallax-Serial-LCDs-Product-Guide-v3.1.pdf which initially makes the serial line high then pauses 100 ms. Powered up/down & backlight on/off dozens of times, no issues, works great.

    I'm impressed. A pity and a joy that the Shack is blowing them out for $10.
  • RDL2004RDL2004 Posts: 2,554
    edited 2013-09-21 03:59
    It's too bad Parallax doesn't sell the board ("backpack") separate from the LCD like almost everyone else does. I don't really like the slime green backlight color, and there are times when having the board soldered directly to the LCD is not convenient. A new model with an RGB backlight might be a good idea.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2013-09-23 08:31
    erco wrote: »
    Would also like to hear more about this from Parallax. Is sending data before applying 5V a bigger no-no than "crossing the streams"? I'll have to play with my pile of new Shack LCDs on Saturday.

    erco,

    It's not a good idea to send data to the module when not powered up since the on-board MCU could go into latch-up given the right conditions. It's not a guaranteed thing, but it can and does happen, leaving the LCD unable to receive data, or worse, completely dead. Here is an article that gives some information on it.

    http://en.wikipedia.org/wiki/Latchup
  • Ron CzapalaRon Czapala Posts: 2,418
    edited 2013-09-23 10:00
    Chris Savage wrote: »
    erco,

    It's not a good idea to send data to the module when not powered up since the on-board MCU could go into latch-up given the right conditions. It's not a guaranteed thing, but it can and does happen, leaving the LCD unable to receive data, or worse, completely dead. Here is an article that gives some information on it.

    http://en.wikipedia.org/wiki/Latchup

    Chris,
    Thanks for the explanation - maybe a bad +5v connection caused dexxterity's problem. Sounds like if the ground was still connected, the data signal cause a latch-up.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2013-09-23 11:55
    There are a few possibilities. I had mentioned noise on the supply line as well, but that would take a scope to determine. I would consider trying a new board on the next LCD Module as an alternative to a new module on the same problematic board.
  • dexxteritydexxterity Posts: 14
    edited 2013-09-25 09:39
    @Chris Savage In the next couple of days I will try my new screen with a fresh protoboard with nothing but the LCD connected.
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