I have a mcp9803 from ncd and I have tried several libraries and none of them are working very well. They go from just plain locking up when the read is issued to a way off temp reading or the reading doesn't change by a few decimal points on a 30 degree real temp swing.
Which libraries did you try?
I tried the one that is inside particle to be added( via add library). That one showed like 4c instead of 24c.
The next once I tried is from a person that is using a controleverything.com board. I don't have the github link for that one. It shows like 15 or 16c no matter what the real temp is.
Then I tried GitHub - Roman3349/MCP980X-arduino: Arduino library for Microchip MCP9800, MCP9801, MCP9802 and MCP9803 temp sensors. and it just locks up the board on read.
Just an update. I went back to the one that is in the particle system and I'm getting 46c instead of 24c.
Is this module the one that you have?
How did you connect it to your device? The NCD nodeLync modules are designed to run at 5V but current Particle devices can only run a 3.3V. The NCD Feather has the level-shifter on it, but if you're using the bare wires, of course they do not.
If you are using bare wires, the MCP9803 should work at 3.3V, however. Connect the 5V pin on the sensor module to 3V3, not VUSB. Make sure you enable the pull-up resistors on the sensor module.
We are using NCD Screw Terminal for the "main" board. It is wired threw their 4 pin cable.
The the main board has the pull ups on it.