MCP3421 is a single channel, low-noise, high accuracy delta-sigma A/D converter with differential inputs and up to 18 bits of resolution in a small SOT-23-6 package. The on-board precision 2.048V reference voltage enables an input range of ±2.048V differentially.
The device uses a two-wire I2C compatible serial interface and operates from a single power supply ranging from 2.7V to 5.5V, has a decent price and looks like a good companion for our ESP8266 module.
I have run some tests and it’s looking quite well for a cheap ADC
Test done in filtered environment - stable voltage
MCP3421 - I2C ADC - ESP8266 Driver - Test in filtered environment - YouTube
Test done in noisy environment - using real bus unfiltered voltage
MCP3421 - I2C ADC - ESP8266 Driver - Test in noisy environment - YouTube
Test done in noisy environment - values are printed directly on CBDB DevBoard LCD Display
MCP3421 - I2C ADC - ES