Grove RGB LCD with Raspberry - Backlight works, Text not

Hi all,

I have a small project with a Grove RGB LCD (V4.0). It is connected to my pi zero which has also a Justboom zero amp attached. And there is a mcp23017 in the i2c circuit, too. Before the display and the MCP there is a level shifter in the bus, making it work with 5V.

Unfortunately, my pi doesn’t detect the i2c address of the text function, that should be 0x3E. “i2cdetect -y 1” only shows the amp (which works also via i2c, at 0x4D), the MCP at 0x20 and all the 3 addresses of the backlight (0x03, 0x62, after restart 0x70). And all of them work correctly. Only the text function is not available and the display shows only rectangles in the first row.
The voltage is at 5V (checked it) and as I read, this might be a reason, I connected a separate LAB dc supply and increased the voltage to even 5.5V. Still no improvement.
Then I exchanged the display with the second one I had in stock. No change.

Furthermore, I had sometime the issue, that my i2c bus broke after connecting the LCD, which means the amp stopped playing and I had to reboot. A little annoying, as this takes some time with my pi zero and vnc connection.

Changing the backlight works fine, but I have no idea why I can’t find the address of the text function at all.
Any ideas?

Thanks in advance :wink: