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Author Topic: 16x2 LCD backlight relay problem  (Read 3091 times)
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The most likely reasons for the display going funny over time that I can think of are:

1. Display overheating. Is it getting warm? Are you quite certain that there really is a built-in series resistor for the backlight, and the way you are connecting the backlight does not bypass it?

2. Supply voltage dropping, possibly because the voltage regulator that is powering it is overheating and going into thermal limiting mode. Put a meter across the 5v supply and see whether you get a steady 5v.
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The most likely reasons for the display going funny over time that I can think of are:

1. Display overheating. Is it getting warm? Are you quite certain that there really is a built-in series resistor for the backlight, and the way you are connecting the backlight does not bypass it?

2. Supply voltage dropping, possibly because the voltage regulator that is powering it is overheating and going into thermal limiting mode. Put a meter across the 5v supply and see whether you get a steady 5v.

Display does not get warm at all! I am 100% sure I am not by passing the built in series resistor. For some strange reason though, the pin 15 and 16 are the other way round comparing to all the other LCDs I've ever used. Pin 16 is +ve and 15 is negative.

The power is also a steady 5 volt.

I am using Arduino UNO also with this. Any known issues with these?

Also I have tested the same sketch for hours on the same Arduino with a blue 20x4 LCD and all is well on that. Of course I swapped the pin 15 and 16 on the blue display.

Thanks.

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OK, unless you have something connected to the contrast adjustment pin that you shouldn't, or a bad connection to the display, or something shorting out the back of the display, then I guess you have a faulty display.
« Last Edit: November 27, 2011, 03:51:21 am by dc42 » Logged

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I really don't know.

I have 2 of the exact same red LCDs and they both behave exactly the same.

As I said, with a blue one all is fine.

Thanks.
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What happens if you don't connect the backlight? The display should still be readable in good light.
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What happens if you don't connect the backlight? The display should still be readable in good light.

Garbage at the start up smiley-grin
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Even if you adjust the contrast pot?
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Correct. Even if I adjust the pot, nothing!
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A bit of an update on this....

If I get a non-insulated small screwdriver and put on either pin 1 or pin 2 on the LCD and shake a bit, the screen does what it normally does when left for a while  smiley-confuse

Any ideas?

Thanks.
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Are you sure you are using the right value contrast pot and have it wired correctly for that particular display? Not all displays use the same contrast pot wiring - refer to the datasheet for the correct arrangement.
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I am sure I am using the correct pot (10k) and have wired it correctly.
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3 pages of post replies and 1 picture, no pictures on the connection or solder job. I'm out of ideas unless you provide some pictures and the spec sheet.
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I have a problem with my software, or maybe it's with my hardware, or maybe it is with the interconnections.  I know that the software is correct so I won't show it to you.  There's lots of hardware like mine out there so I won't tell you which I am using or give you a link to the data sheet.  Anyway I know that there are no idiosyncracies associated with my particular hardware.  I know that my connections are perfect so I won't show you a photograph since I don't need you to check those connections, besides I already gave you a nice fuzzy picture of the display, what else could you need?  There may or may not be any consistency in what shows up on the display, you can take a guess.  I told you that initially everything is shown properly on the display, except when that does not happen.  I can 'play' with the potentiometer and get things to change but you can figure out what I mean by that.  The power is steady but I won't tell you the conditions under which I measured it.  You can ask me specific questions but I won't answer all of them.  I live in Zeroland so if you want to give me any information specific to my location you can't.

Please help me.
   

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