A simple interface of MCP23017 with Rpi using I2C lines. Since there is already an internal pull-up resistor of 1.8k on rpi I didn't use any pull-ups n I2C lines.
i2cdetect -y 1 on rpi I rarely receive any response from MCP23017. Most of the times it's unresponsive and while trying to debug it on HW level I observed:
- SDA line show 3.3V sometimes and sometimes 0.5
- SCL line is always 0.5 to 0.7.
When I remove the connection and test only on I2C lines of Rpi, it works as expected. I believe the schematic is fairly simple and should work.
I have created multiple boards and only 1 board works and only 1 MCP responds on the same. I have tested with both; VCC = 5V & 3.3V but no change in observation. I have been struggling with this for more than a week and I can't think of any potential root cause now.