I2C LCD not displaying, I2C scanner shows 0 devices found

Arduino Uno 1.6.7
testing with both an LCD 20x4 and 16x2

for a while I was happily learning about I2C and LCD display.
I installed the library - LiquidCrystal_I2C
removed the LCD library from Arduino standard library
soldiered the I2C to the 16x2 display.
everything was working well and I was able to see text in the display.

something happened, I am not sure what, that caused the LCD to no longer display.

I’m not sure where to look further for the problem.
here is what I know so far:

connected GND, VCC, SDA, SCL, from the I2C board to the arduino - GND, 5v, digital 4, digital 5
red Power LED lights up on the I2C
the backlight still lights up.
I am able to run other sketches which involve a potentiometer and led lights.
I ran the I2C scanner Written by Nick Gammon. It returns: 0 devices found.
I tried attaching a different LCD - 20x4. and adjusted the sketch, buts still no device found. and no text displayed.

i used the only diagnostic tool I could find to see if there might be an issue with it.
// Arduino ShowInfo
it again did not find an I2C, but the other tools reported back data. (it appears to be ok)

I’m wondering if wires accidentally touched the underside of either board to cause a short?
maybe miswired GND and 5v by accident?

like i said they were working for a short time when I had just started to use the 16x2 LCD and I2C board. any suggestions or help is greatly appreciated. see pictures attached.

turn it off and back on. i2c sometimes has issues and a full power off helps.

I do have the kind of same problem I was using the lcd for a long period of time until decided to change my hardware configuration, now I can't get it back to work.

when I ran the i2c scanner, sometimes I get back

" Scanning... Unknow error at address 0x27 No I2C devices found

" I tracked the problem down to the wire.endTransmission () were it gave back 4 meaning just "other error". reading the ic pdf and some info on the wire library I found that the address is used by the library to get the ack byte. has someone an idea of what shoud I do ?

First try without I2C devices connected; the error should change to 2 (address send, NACK received) indicating that nothing was connected.

If you still get 4 with nothing connected (the only reference I can find is that it means that the master lost the arbitration in a multi-master environment), it could be that you have a short somewhere on your Arduino board.

Lastly you can try another I2C device (RTC clock, 2nd Arduino configured as slave (there is an example for that somewhere in the playground)) if you have one available.

Hi there, thanks fpr the reply. I did try out that before posting (I should have told..) I can scan w/out problem other i2c devices like nvram and rtcs... I did check all the conections 3 times and don't find anything weird, so right now I'm assuming that I burned the ic when was handling it.. the only other idea I have is> the lcd i2c adapter is connected to a different power supply and not to the arduino (it is measuring 4.99 v using 2 different voltimeters) (sda scl are connected to arduino)so I asume nothing should happen there but don't know for sure.

in the afternoon I will try out w/ an other I2c lcd adapter

I hope you have the grounds connected between the two devices.

Gad, REALLY? Digital 4 & 5 for I2C...............

????

Try A4 & A5,,, and READING up on I2C.

123Splat: Gad, REALLY? Digital 4 & 5 for I2C...............

????

Try A4 & A5,,, and READING up on I2C.

You're replying to a post of nearly a year ago ;) I did not even read that one when I saw the date :)

Good catch anyway.

sterretje: I hope you have the grounds connected between the two devices.

Nop I dont have them connected... does it happen something ?? how should I connect them together ?

123Splat: Gad, REALLY? Digital 4 & 5 for I2C...............

????

Try A4 & A5,,, and READING up on I2C.

didn't see that one either.. however Im using A4 & A5..

sterretje: You're replying to a post of nearly a year ago ;) I did not even read that one when I saw the date :)

Good catch anyway.

Read again....... re-open by another user with same problem.......

gndpl22: Nop I dont have them connected... does it happen something ?? how should I connect them together ?

didn't see that one either.. however Im using A4 & A5..

Not in your post ( specified "D4" & "D5"), or the picture ( shown connected to D4 & D5)....... Though, it isn't your picture.

If you have Arduino 5V, Arduino GND, SCL, & SDA connected to the I2C board, you have the grounds connected. Re-check your wiring.

EDIT: My bad.. I attributed the first post to you, sorry. But re-check your wiring just the same. A common issue with wiring I2c peripherals is inadvertently swapping SCL & SDA between Arduino and peripheral.

Your system needs a common ground. Just connect the GND of the lcd i2c adapter to both the Arduino and the second power supply.

Current needs to be able to flow back to it's source; so current from the Arduino (SCL and SDA pins) needs to be able to flow back to the Arduino and current from the second power supply needs to be able to flow back from that second power supply.

Hi there,

finally I did connect the ground of my 5v supply and the arduino ground... guess what... IT WORKS !!!!

So just in case anyone else has a set up with a i2c device and an external 5v supply and gets the error 4 from the i2c scanner , connect the 2 groud together, the i2c scanner now shows the device and works like a charm

thankyou guys for your help

I have the same problem but on my circuit SDA is connected to A4 and SCL to A5. The VCC is connected to +5V and the GND to GND. I'm using Arduino Mega 2560 connected to LCD 1602 with PCF8574T chip i2c.

using the i2c scanner in reported "No I2C Devices Found".

For an Mega2560 you don't use A4&A5 but pins 20 (SDA), 21 (SCL).

I had a similar problem. My display always returned error code 2 even I connected it properly. I followed these instructions: https://www.instructables.com/id/LCD-With-I2C/ The problem was that I should connect SCL to A5 and SDA to A4 (the opposite way as it was written in the tutorial). Then everything worked as expected.

1 Like

So you followed an "instructables" article and had problems?

Couldn't see that coming. :astonished: