How to connect LCD 2004 to Arduino using I2C?

Question

Arduino

Good day.
Available:
1. Arduino (Funduino Uno and Mega 2560 clone)
2. LCD 20 * 4 bought on Aliexpress
3. I2C interface for them ( bought in the same place )
Screen, when power is applied, it goes into self-testing, the backlight also works - I think that it is working .
PCF8574, when connected to Arduino, scans perfectly at 0x20 and 0x27 (with jumpers) - it also seems to be working. But when connecting LCD and PCF8574, the latter stops responding to scanning. When you turn on the Arduino, the screen blinks once and does not show any signs of life, but if you remove the jumper from the LCD backlight, the PCF8574 starts responding to scanning again. It obviously shouldn't be that way. Well, of course, none of the libraries launched the LCD. What am I doing wrong?

Answer 1

If I understand correctly, here are the solutions

Answer 2

- Make sure you are using the LiquidCrystal_I2C library (downloaded separately).
- Make sure the display is working correctly - connect directly to the arduino via 6 wires (excluding power and backlight). Something like this for example. Diagnose the display itself.
- Make sure that I2C and display are in good contact. I also caught devils in a snuffbox until the display moved my finger.