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Author Topic: No contrast on LCD screen  (Read 838 times)
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Ok so i followed this tutoial  http://learn.adafruit.com/character-lcds/wiring-a-character-lcd   with a  HD44780 lcd and have it all wired up. I think, yet when i twist the petentiometer nothing happens, no rectangles or anything of that nature. It looks exactly the same. Pictures attached. Thank you!!


* IMG_3811.JPG (1965.13 KB, 4000x2248 - viewed 25 times.)
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Your wiring looks OK to me.  Perhaps the there is a bad spot in the prototype board.  You should move your component to new positions.
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Are you sure pin 1 is on the left in the photo?
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Make sure that your power supply hasn't shut down due to excessive backlight current.  Have you considered using a current limiting resistor with the backlight?

Don
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Ok one other thing that looks very strange in your photo is the 16 pin header.
I see that the short part of the header pins and plastic is on top of the LCD PCB.
with the longer pins going through the LCD PCB.
This is quite unusual.
Compare the difference in looks between your setup and the pictures
on the adafruit tutorial. (in particular the 3rd photo down)
While the header can be inserted this way and the long pins soldered on the bottom,
normally the the plastic is under the LCD PCB and the short pins are soldered on the top.

Did you follow the tutorial and solder the pins to the PCB or are you just sticking the header through the
holes in the LCD PCB and into the bread board?


--- bill

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Make sure that your power supply hasn't shut down due to excessive backlight current.  Have you considered using a current limiting resistor with the backlight?

Don

I think I did at the beginning but I removed it. Will try again though.
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Ok one other thing that looks very strange in your photo is the 16 pin header.
I see that the short part of the header pins and plastic is on top of the LCD PCB.
with the longer pins going through the LCD PCB.
This is quite unusual.
Compare the difference in looks between your setup and the pictures
on the adafruit tutorial. (in particular the 3rd photo down)
While the header can be inserted this way and the long pins soldered on the bottom,
normally the the plastic is under the LCD PCB and the short pins are soldered on the top.

Did you follow the tutorial and solder the pins to the PCB or are you just sticking the header through the
holes in the LCD PCB and into the bread board?


--- bill



My header strip was not long enough so I added an extra, I must have placed it in the wrong way. I will change it around and see if it makes a difference. Also no, I have not soldered it. I have never soldered anything and would rather be able to reuse this breadboards. Also will soldering really do anything other than make it permanent?
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Also no, I have not soldered it. I have never soldered anything and would rather be able to reuse this breadboards. Also will soldering really do anything other than make it permanent?

No solder = Will Not work!

The header must be soldered.

The tutorial you linked to in the 1st post even warns about this in the second paragraph:

Quote
Next you'll need to solder the header to the LCD.You must do this, it is not OK to just try to 'press fit' the LCD!



--- bill
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Quote
Compare the difference in looks between your setup and the pictures on the adafruit tutorial. (in particular the 3rd photo down)
Bill - Adafruit changed the tutorial recently and I am not sure that I will recommend it any more.  They have switched back to selling a version of display that uses a low power backlight with a current limiting resistor on the pc board so they have removed the recently added information on how to determine the required series resistance from the tutorial.  The photos never did show the resistor. (They do have a disclaimer that the tutorial is only for their products.)  Also, they still have the first bunch of photos with the LCD shown upside down, so the single row of blocks appears to be on the bottom, not the top.

Don
« Last Edit: July 18, 2012, 08:44:00 am by floresta » Logged

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Also no, I have not soldered it. I have never soldered anything and would rather be able to reuse this breadboards. Also will soldering really do anything other than make it permanent?

No solder = Will Not work!

The header must be soldered.

The tutorial you linked to in the 1st post even warns about this in the second paragraph:

Quote
Next you'll need to solder the header to the LCD.You must do this, it is not OK to just try to 'press fit' the LCD!



--- bill


What will soldering do that is different than 'Pressing fit' The LCD?
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OK! I think this might be it! i started moving the screen around a little bit on the pins and then this showed up!. Depending on how i move it contrast shows everywhere but the top left corner



* IMG_3818.JPG (1865.71 KB, 4000x2248 - viewed 8 times.)
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What will soldering do that is different than 'Pressing fit' The LCD?

Again, I can't stress this enough.
No solder with header = Will not work!

The holes in the PCB are just that, holes. The are there to be used for soldering.
They are not a socket and are not designed to be used used with any sort
of mechanical press fit. The fact that you are seeing anything on the screen is pure luck.

You simply can't use it the way you are trying to use it.
The tutorial you referenced even explicitly warned about not trying to do this.

Time to break out the soldering iron and solder the header to the LCD PCB.

--- bill

Don,
I'm not a particular fan of the Adafruit tutorial either, but I referenced in because
it was referenced in the original post that said:
Quote
Ok so i followed this tutoial ...
I was trying to point out that essentially the very fist step of the referenced
tutorial was not being followed.

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What will soldering do that is different than 'Pressing fit' The LCD?

Again, I can't stress this enough.
No solder with header = Will not work!

The holes in the PCB are just that, holes. The are there to be used for soldering.
They are not a socket and are not designed to be used used with any sort
of mechanical press fit. The fact that you are seeing anything on the screen is pure luck.

You simply can't use it the way you are trying to use it.
The tutorial you referenced even explicitly warned about not trying to do this.

Time to break out the soldering iron and solder the header to the LCD PCB.

--- bill

Don,
I'm not a particular fan of the Adafruit tutorial either, but I referenced in because
it was referenced in the original post that said:
Quote
Ok so i followed this tutoial ...
I was trying to point out that essentially the very fist step of the referenced
tutorial was not being followed.



Ok i get it! Thank you! Time to learn how to solder i guess!
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Depending on how i move it contrast shows everywhere but the top left corner
That type of display defect is sometimes caused by a poor connection between the LCD 'glass' and the PC board.  If you still get that display after you have soldered the header pins then you will have to try and tighten the black bezel by twisting the tabs where they protrude through the PC board.

Don
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Ok i get it! Thank you! Time to learn how to solder i guess!

Not on your new LCD though... If you have never soldered before, while it's not particularly difficult I'd suggest you practice on some cheap resistors etc first.
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