Issue with LCD with i2c backpack

Using Arduino Displays
1

Hello everybody,
I am having a problem with my LCD connected to a Uno Rev3, it used to work just fine but not anymore.
This is the display:

71-V7xugSCL.AC_SL1500
71-V7xugSCL.AC_SL15001392×1488 192 KB

The soldering looks good, here's a picture:
IMG_20241128_103350
IMG_20241128_1033501920×1437 119 KB

IMG_20241128_103226
IMG_20241128_1032261920×1437 235 KB

This is the result from the diagnostic tool (hd44780's I2CexpDiag):

Serial Initialized
--------------------------------------------------------------------
I2CexpDiag - i2c LCD i/o expander backpack diagnostic tool
--------------------------------------------------------------------
hd44780 lib version: 1.3.2
--------------------------------------------------------------------
Reported Arduino Revision: 1.6.7
CPU ARCH: AVR - F_CPU: 16000000
--------------------------------------------------------------------
SDA digital pin: 18 A4
SCL digital pin: 19 A5
--------------------------------------------------------------------
Checking for required external I2C pull-up on SDA - YES
Checking for required external I2C pull-up on SCL - YES
Checking for I2C pins shorted together - Not Shorted
--------------------------------------------------------------------
Scanning i2c bus for devices..
Total I2C devices found: 0
No I2C devices found

The display turns on, the contrast is set already (as I said it used to work), now the address doesn't get detected at all and I can't display any text to it. There's nothing on A4 and A5 pin.
Does anybody have an idea of what the problem may be?
Thanks in advance, I don't know anymore what to try besides buying a new LCD

2

What does this mean .. no wires or no pulses?

Edit: The LCD does not have an address only the backpack.
Check your wires or the backpack may be faulty.
A5 is CLOCK.
A4 IS DATA.

3

I have read a topic in which the problem had been solved by removing what was connected to A4/A5 (since they can be used as SDA/SDL as well). I just listed everything I have tried and didn't work, in order to not get the same suggestions

4

Did you make any changes on the wiring from when it worked or any changes in the Code?

5

Have you tried the I2C Scanner sketch to see if anything gets detected on the I2C bus?

If nothing detected I suggest you to check your wires and perhaps change breadboard. In the past I've had issues with iffy breadboard connections and faulty connection when using long jumper wires.

6

I did already, doesn't find any device and keeps scanning.
I already checked the wires as well, moreover the SDA and SCL cables are direct from Arduino to the LCD, therefore the breadboard isn't the issue

7

Always the same wiring, didn't make any change (it's two direct wires)

8

Did the driver board and display arrive soldered together?
Some do, some don't. Check the solder.
No sense going any further if i2c_scanner doesn't detect it.

9

What do you use for power?

10

They arrived already soldered, and the soldering looks pretty solid

11

5V from Arduino with 200Ω resistor

12

Is the 200ohm resistor in series with the power , can you measure the Voltage on the backpack?
There will be a significant drop in Voltage across the resistor due to the LCD back light.

13

Yeah it's in series, the measurement is 3.33V

14

I am almost 100% sure that's your problem the LCD does not work on 3.3V (Believe me I tested that) must be 5V.
Remove the resistor.

1 Like
15

It's so silly that I would have never thought about it (also cause when I tested it - I did with the resistor and it worked), it finally works! Thank you so much for your help, I really appreciate it

16

I am glad it works now.