Read data from MCP9808

I think most likely what's happened is device hasn't been recognised - it looks like during the var mcp = require("MCP9808").connect... line there might have been an error reported. If that failed then mcp wouldn't get set - but if you're uploading to RAM then the lines are executed one by one so the next lines would still get executed.

As you'd found with the MAX30102 chip, there could be some reasons why the device isn't discovered using I2C.

• Maybe there are no pullup resistors - you could use software I2C and see if it's any better:

  var i = new I2C();
  i.setup({scl:D25,sda:D26, bitrate: 60000});
  var mcp = require("MCP9808").connect(i, 0b000); 
  

• But maybe sda/scl are around the wrong way, grounding it wrong, etc

• Or maybe the address isn't 0b000 is A0/1/2 aren't GND