I'm having trouble driving a 20x4 I2C LCD. I'm new to I2C and am finding some conflicting information regarding the Arduino Nano as to what pins are the I2C pins. I've got a version 3.1 Nano, some info says A4 and A5 are the I2C pins, other info says pinout has been reversed and it's A2 and A3.
The LCD lights up but the I2C LCD Library "Hello World" doesn't show. I've also read conflicting information about a pull up needs to be enabled on the pins or perhaps is through the library? So my questions are, which pins do I use, do I have to alter the defaults in the I2C library or Wire library, if so where are those defaults (I couldn't see them).
It's not the contrast pot and I'm using the address marked on the back of the I2C on the LCD, 0x27. Thanks.
You will get a more reliable answer if you post a better description or a link to the actual device.
I'm using the address marked on the back of the I2C on the LCD, 0x27.
If the manufacturer of the I2C adapter (I assume you are using one) has not obliterated the IC part number then we should also have this information. For example, if the chip on your I2C interface board is a PCF8574A then the I2C address is 0x3F, if it is a PCF8574 (without the 'A' suffix) then the I2C address is 0x27. The two devices are identical except for the I2C address.
If the manufacturer has obliterated the part number then complain to SainSmart.
It was 0x27, to get everything working I had to use an older version of LiquidCrystal_I2C linked on the DFRobot product page for this i2c LCD 2004, after swapping that library in, using pull-up resistors and pin A4 and A5 of the v3.1 nano the LCD works as expected.