I2C LCD backlight is not lighting up

My LCD backlight is not lighting up. But the words are showing up.
The code:

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

// LiquidCrystal_I2C lcd(0x27, 16, 2);
// OR
LiquidCrystal_I2C lcd(0x3F, 16, 2);

void setup(){
lcd.print("TA DAA...!");
void loop{
// do nothing here

My I2C LCD is some Chinese board
Thank you for your help.

Jumper is set?
Post a picture of the wiring and the backpack itself.
Post a link to the product you have bought.

This is the link: I2C Module for Character LCD

And for the pictures are bellow (link because it is too big sorry)



I don’t believe you. The photo in the Cytron link shows a PCF8574T chip. Your sketch uses slave address = 0x3F. ( 0x3F is for a PCF8574AT )

Google blocks access to your second photo. i.e. the one that probably shows the backpack.


Oh sorry, I have realized that. I will send the second photo again and the programming i will chang it to 0x27(The location of my I2C)



How to post images so we don't have to download them and everyone can see them.
How to post an image.
Another page on posting images.

But when I use the method above, it says that it is too big, what should I do when this happens?

Put a jumper over the two pins marked LED. Then the LED will work.

I strongly advise you to install the hd44780 library via the IDE Library Manager.

It worked but shouldn't the contrast of the words be sharper?

try to adjust the blue potentiometer with a screwdriver.

I tried but that is the maximum.

What is the supply voltage to the LCD? Measure the voltage with a meter.

5 Volts

Here is the model nmber of the I2C: PCF8574A And the lcd is a QAPASS Ui also. www-myascension.org/: I don't have a spec sheet and the LCD seems to show empty chars when rotating the pot.

Here is the model number of the I2C: PCF8574A And the lcd is a QAPASS Ui also.

So you seriously have no idea whatsoever what the “QAPASS” sticker means? :roll_eyes:


That appears to be total nonsense.

I don’t have a spec sheet and the LCD seems to show empty chars when rotating the pot.

Here is the spec sheet.

The correct position for the potentiometer is when you see “blocks” on the first line only. But the fact that you do see the blocks means the display is not responding to your code.

We advise that you do not use the older “LiquidCrystal” libraries but go to the library manager, install the “HD44780” library and work through the examples provided with that library for the I2C version, starting with the testing sketch.