Can't get LCD 1602 I2C show any characters

I just watched the video, and I think there is a problem with the contrast potentiometer.

The backlight should not go off at one end of the pot's travel. The backlight should not be interactive with the contrast. The going dark, actually looks like some sort of short at one end of travel.

With only power connected to the lcd(and not SDA and SCL) and no program loaded, the backlight should be on, and you should be able to turn the contrast pot to produce dark or light square on the top row of the lcd. The squares should be near the low resistance end of the pot.

EDIT Tom George spotted the fact that the Arduino power light is going off at the same time the backlight goes off. There is definitely some sort of short.

Hi, Did you install the I2C board on the back of the display, or did it come completely assembled. Their is a fault in the connections between the display and the I2C PCB by the looks of it, in fact at times the power light on the UNO goes out indicating a possible short. Check the connections between the boards where the solder joints are, make sure there is no bridging from stray wire strands. Also check the 5V on the UNO to make sure your computer is supplying enough power.

Tom..... :)

TomGeorge: Hi, Did you install the I2C board on the back of the display, or did it come completely assembled. Their is a fault in the connections between the display and the I2C PCB by the looks of it, in fact at times the power light on the UNO goes out indicating a possible short. Check the connections between the boards where the solder joints are, make sure there is no bridging from stray wire strands. Also check the 5V on the UNO to make sure your computer is supplying enough power.

Tom..... :)

I got it completely assembled and I can do nothing with I2C, because it tightly connects to LCD module (or can I?). 5V is ok, i even try 9v battery.

HI, Is there anything to stop the two boards from making contact with each other and shorting? Is there an insulation sheet of some sort between them?

Tom.... :)

TomGeorge: HI, Is there anything to stop the two boards from making contact with each other and shorting? Is there an insulation sheet of some sort between them?

Tom.... :)

Nothing that I can see

On my module, running the pot to one end of its travel does not make the backlight or the arduino power lights go off.

If you can not observe dark/light squares on the top row of the lcd with the potentiometer you will never be able to see text.

Can you provide a photograph of the back side of your module, so that the pot is clearly shown?

cattledog:
On my module, running the pot to one end of its travel does not make the backlight or the arduino power lights go off.

If you can not observe dark/light squares on the top row of the lcd with the potentiometer you will never be able to see text.

Can you provide a photograph of the back side of your module, so that the pot is clearly shown?

Iā€™m sorry, I have only a web cam. Is it ok?

If you can't see squares on the display when the pot is near one end of its travel, you will not be able to get it to work properly. If you adjust carefully near the end where the pot shorts out, can you see squares?

The display can work without a pot by using a fixed resistor from the Vo pin to ground.

I think you may be at the point where you have to decide whether to return the display or to start modifying it.

cattledog: If you can't see squares on the display when the pot is near one end of its travel, you will not be able to get it to work properly. If you adjust carefully near the end where the pot shorts out, can you see squares?

The display can work without a pot by using a fixed resistor from the Vo pin to ground.

I think you may be at the point where you have to decide whether to return the display or to start modifying it.

I want to try to modify it. Can you help me?

Do you have a soldering iron, and a supply of resistors from 2K to 220 ohms?

A soldering iron I'll have in days; resistors I surely have.

Here's something quick to do to see if there is hope.

Connect the display to 5v and GND. Set the pot to the center of its range. Place one end of a 1K resistor into a female ground pin on the Arduino.

Then use a jumper wire to contact the free end of the resistor and touch the other end of the jumper to the Vo (contrast pin)3rd pin from the left when looking at the display. You may have some difficulty making firm contact with either the resistor or the solder bump on the display . You should see white blocks. If you don't see them, try a bigger or smaller resistor. Try some different positions on the pot, but stay away from either end. If there is no change in the display, it may not be fixable.

I tried, 10k, 2k, 1k, 220, 200, 100, 10. 10k 2k, 1k - no effect. 220, 200 and 100 - reducing (backlight) power. 10 - shorts

I tried, 10k, 2k, 1k, 220, 200, 100, 10. 10k 2k, 1k - no effect. 220, 200 and 100 - reducing (backlight) power. 10 - shorts

Not very encouraging results. I think that from here, your choices are to return the display, remove the potentiometer from the back, or remove the i2c adaptor from the display.

The potentiometer is held on by three through soldered pins. If you leave the adaptor on the display, a dremel tool grinder to grind it off, or a jewelers wire saw to try and sip under one edge and saw through the pins might be options.

I'm not hopeful, and can't quite see a mechanism where a defective pot would prevent the direct connection of a resistor to ground from working.

Have you used a multi meter and confirmed GND and 5V on the VSS and VDD pins of the display? They are the first and second pins from the left when looking at the display. We know the back light is getting power, but its not certain that the display pins (and display controller) are actually powered from the header.

The other route, is to remove the entire i2c adaptor from the back of the display, and confirm that the display itself will work in parallel mode. There may be defects in the lcd board itself which could prevent the contrast from working. If the display is bad, at least you will have an intact i2c adaptor. Once the adaptor is off the display, you can cleanly remove the pot from the adaptor if the pot is really the problem.

If you take off the pot, and later take off the adaptor, then you won't have an intact module, but you could use the direct resistor from Vo to ground on any other display you want to put it on.

Quote from: TomGeorge on Today at 07:09:42

HI, Is there anything to stop the two boards from making contact with each other and shorting? Is there an insulation sheet of some sort between them? *Tom.... :) *

Nothing that I can see

Can you slip a piece of plastic or card board between them to make sure you aren't shorting anything out? Tom.... :)

TomGeorge: Quote from: TomGeorge on Today at 07:09:42 Nothing that I can see

Can you slip a piece of plastic or card board between them to make sure you aren't shorting anything out? Tom.... :)

Can we back-up?

Backlight works-via I2C controller. The I2C module power LED , next to backlight jumper, is on?

Are pins 1 & 2 on the LCD module itself connected / soldered to power - both GND and +5V? They are definitely not shorted - would have no power anywhere.

Contrast pot does nothing. ( Where on the PCB itself is the +5V / GND connected to the pot?)

Powering V0 directly from GND ?? does practically nothing - should that be +5V anyway?

The I2C controller board and the LCD module are NORMALLY connected / soldered together using .1 header WITH plastic spacers. ( Resolder is OK, removing / un-soldering MAY not be worth the effort )

So far we have not seen:

  1. picture of back of the LCD module under power ( red LED on?) - but a brief reflection of the red power LED being on. ( not a good idea to move the LCD module around while powered - jumper wires can get broken that way easy - they are not designed to be moved around !)

  2. side view of the .1 header showing the plastic spacers

  3. voltage between pins 1 & 2 on the I2C AND LCD module ?

  4. voltage (variable?) between pins 1 and 3 ( GND / V0) on LCD module ?

@asyler - Did you buy this new? (Or is it a cast-off, a 'gift', etc.?)

@cattledog : I decide to return it (if possible). Btw, I can't remove the i2c adaptor from the back of the display (they connected very firmly).

@TomGeorge : no effect

@Runaway Pancake : I bought it on AliExpress.

Vaclav, i can only say that I2C LED is on.

Looking at the front of the display and measuring off of the soldered pins, please measure the voltage of pin1 to ground and pin2 to ground and to each other. We really have not confirmed that power is getting to the display as well as the backlight. If power is not actually getting to the display, it would explain why the contrast does not work with the resistor to ground.