LCD I2C connection problems

Question

I am hoping there is a simple fix to this problem.

I am playing around with a 16x2 lcd with a I2C connector attached. I wired it up to an elegoo uno R3.

I started with some code I've used before and ended up with one row of the LCD fully lit and the other dark.

After a ton of trouble shooting, I can not get the LCD to show anything but one lit and one dark row.

In this image:

Power: 5V, 1.5A

Pin	LCD	Uno
SCL	SCL	SCL
SCA	SDA	SDA
+	VCC	5V
gnd	gnd	gnd

I've also tried:

• putting the SDA to A4 and the SCL to A5
• Using different power supplies
• Powering from the USB connector

And I've tried several of the libraries available

They are all variations of the following from the Adafruit_LiquidCrystal library:

#include <Wire.h> 
#include <LiquidCrystal_I2C.h>

// Set the LCD address to 0x27 for a 16 chars and 2 line display
LiquidCrystal_I2C lcd(0x27, 16, 2);

void setup()
{
    // initialize the LCD
    lcd.begin();

    // Turn on the blacklight and print a message.
    lcd.backlight();
    lcd.print("Hello, world!");
}

void loop()
{
    // Do nothing here...
}

No matter what I do the display does not change.

Answer 1

Some common problems with LCD displays which incorporate an I2C backpack include:

1. Not using the correct I2C address for the I2C backpack. Use an I2C scanner to discover the correct address.
2. Mixing voltages without proper level shifting, say using a 5v display with a 3.3v MCU
3. Failing to adjust the contrast potentiometer
4. Some I2C backpacks may use a non-standard pin allocation which may be corrected by specifying a pin mapping in the constructor to the display library. Fortunately, this is rare.
5. Using code samples intended for a different variant of the library supporting the display. Always use a basic test sketch which is packaged with the chosen library to verify the performance of the display.