2 LCD i2c didnt work, help me.

Hello.
I have two LCD whit i2c backpack and didint show just a lot of boxes in the first row.
I try a lot of code but didnt work.
Anyone can help me, i need solve this fast.

No, we can't help because you did not give enough information. Imagine for a moment that we do not have psychic superpowers, and that we are just ordinary geeks. What information do you think we would we need from you? Imagine we are there in the room with you. What would you show us?

So i have two LCD whit i2c backpack and i scan i2c adresses for the first one is 0x3F and the second one is 0x27 .
the contrast is setted good (i think)
i copyed a i2c lcd code but my lcd is a chinise cheap lcd and didint work whit thehe codes.
i dont no what i do now.
i need sole this problem for next monday. :frowning:

Ok, a small improvement. Are you saying you have tried the i2c scanner sketch?

Have you tried the "i2c LCD guesser" sketch?

https://codebender.cc/sketch:194516#i2cLCDguesser.ino

i tryed the i2c scanner but the i2c guesser not hwo can i try the sketch says it can damage my hardware.
Its ok?

I think you have to take that risk. Otherwise maybe you will never find out how to use these displays. This is a risk you must accept when you buy cheap Chinese components. I think the risk is small. It is a worthwhile risk because you save some money. The guesser sketch did not damage my i2c LCD display.

okay, i accpet risk but can you help me how to use lcd guesser?

Upload the sketch to the Arduino. Follow the instructions on serial monitor and watch the LCD.

Thanks, i try it.

I try it but no result just my LCD screen is black and blink some times.
But the guesser fount the i2c adress(0x3F) after the test my LCD screen is still black what is happening?

Did you try your other LCD also? The one with address 0x27?

Can you post links or pictures of your lcds? Including close-up, clear pictures of the packpacks.

Oh got it the orange one lcd is working
But the blue one is not.
But a BIG THANKS! :slight_smile: 8)

It could be that the blue lcd is faulty. Or maybe the blue lcd has a chip or backpack that the lcd guesser does not work with.

The lcd guesser performs several actions. First it tries to find the i2c address of the chip on the backpack, in the same way that i2c scanner works. This is why lcd guesser correctly reports the address. Next, it tries to guess the type of chip, based on the address. Then it tries to guess the connections between the chip and the lcd module. Different manufacturers may use different connections. The lcd guesser does not try every possible combination, only a few combinations that are known to have been used. Maybe your backpack is an unusual one.

Post the lcd guesser output you see on Serial Monitor with the blue lcd connected (please use code tags).

here is my blue lcd output in the test no text show:

i2cLCDguesser v1.4.1
 - Guess constructor for i2c LCD backpack
----------------------------------------------------------------
NOTE/WARNING: Guessing the i2c constructor is not really a
good thing since it could damage the hardware. Use with caution!
Do not leave things with an incorrect guess for too long.
i.e. advance to the next guess as soon as possible
when the guess in incorrect.
If the guess is correct, the constructor will show up
on the LCD.
----------------------------------------------------------------

<Press <ENTER> or click [Send] to Continue>
Scanning i2c bus for devices..
i2c device found at address 0x23
Device found: PCF8574
<Press <ENTER> or click [Send] to start guessing>
Trying: lcd(0x23, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE)
<Press <ENTER> or click [Send] to Continue>
Trying: lcd(0x23, 2, 1, 0, 4, 5, 6, 7, 3, NEGATIVE)
<Press <ENTER> or click [Send] to Continue>
Trying: lcd(0x23, 4, 5, 6, 0, 1, 2, 3, 7, NEGATIVE)
<Press <ENTER> or click [Send] to Continue>
Trying: lcd(0x23, 6, 5, 4, 0, 1, 2, 3, 7, NEGATIVE)
<Press <ENTER> or click [Send] to Continue>
Trying: lcd(0x23, 6, 5, 4, 0, 1, 2, 3, 7, POSITIVE)
<Press <ENTER> or click [Send] to Continue>
Trying: lcd(0x23, 4, 5, 6, 0, 1, 2, 3, 7, POSITIVE)
<Press <ENTER> or click [Send] to Continue>
Scanning i2c bus for devices..
i2c device found at address 0x23
Device found: PCF8574
<Press <ENTER> or click [Send] to start guessing>

I'm out of ideas. How about posting those links/pictures?

Did you solder the backpack on yourself? If so, might be worth re-melting each joint with the iron and adding a tiny bit more solder.

Yes, i soldered myself but i think im soldered perfectly and here the imege: (back and front)

I can't judge your soldering skills from those photos, so I must believe you about that.

The backpack looks pretty standard. The LCD guesser should have worked. My best guess at this point would be a faulty component, either the backpack of LCD itself.

ProArduino551,
I'm the author of the guesser sketch.
I have moved forward with an improved library package that I believe is better and is much easier to use.
I would recommend using it instead - or at least giving it a try.
It is called hd44780. It is available in the IDE library manager so you can quickly install it.
It will not interfere with any other library that is installed.
You can read more about it here: GitHub - duinoWitchery/hd44780: Extensible hd44780 LCD library
There is also additional information in the wiki on the github page.
The i/o class you will use for that type of backpack is hd44780_I2Cexp.
Run the included diagnostic sketch I2CexpDiag first to test everything.
It will test the i2c signals, and the LCD module RAM to verify that the h/w and library are properly communicating.

The advantage of using the hd44780_I2Cexp i/o class from the hd44780 library is that it can auto detect everything.
This means you don't have to enter the i2c address or any of the pin mapping information in your sketch.

In your specific situation it also means means that you can swap out the LCD modules, press reset or power cycle the Arduino, and a sketch will still work without having to recompile the sketch, even when the i2c addresses or pin mappings are different.

Not only is hd44780 faster than other libraries, but it also has some extra features not available in other libraries.
Overall, it is a much better and easier to use solution than using the guesser sketch with fm's new LiquidCrystal library.

--- bill