The 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.
For more details : http://www.esp8266-projects.com/2015/04/18-bit-adc-mcp3421-i2c-driver-esp8266.html
Videos:
1. Test done in filtered environment - stable voltage
2. Test done in noisy environment - using real bus unfiltered voltage
3. Test done in noisy environment - values are printed directly on CBDB DevBoard LCD Display
Available on Tindie: https://www.tindie.com/products/nEXT_EVO1/universal-ac-mains-dimmer-mpdmv41/