Reasons for no ACK: The address of mcp3421 is configured incorrectly, the silk-screen model is CB5R, and the address should be 001 instead of the default 000
The IIC address of this IC is not fixed. It is determined according to the silkscreen on
the IC. The IIC address of each batch of factory ICs is different. Therefore, if you use someone else’s code, it doesn’t always work. It depends on what you have on hand. Determined by the silk screen of the IC