4 x 20 LCD via I2C : doesn't boot up correctly

Hi everyone,

My electronic start sequencer based around an Arduino MEGA now works kind of ok so I can focus on non-essential problems :slight_smile:

Here it is : my Arduino MEGA is controlling a 4x20 LCD display via I2C (SDA/SCL), it's this model :

The whole electronic sequencer is supplied by a 12V battery.

Now, when I turn on the battery that feeds everything, the LCD and MEGA boot up just perfectly fine and all is OK.

BUT! When, for example, I connect my laptop to get the serial link and the MEGA resets because I open Processing (which in my sketch opens up the serial --> MEGA reset), the LCD gives unreadable (out of sync?) readings 3 out of 4 times. And for some reason, some times it will boot up fine.

I suspect that the +5V that's supplied from both the Laptop and the battery are messing with one another somehow but I have no idea how or how to resolve this situation... So for now I just reset it until it works (PITA!).

Thanks for the help!


Since your LCD is interfaced via I2C the problem would more likely be with the sketch and/or the specific I2C library that you are using rather than the particular LCD module. If you are requesting help then we need more information.