The use of the ESP8266 in the world of IoT

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By martinayotte
#55729 The spec of MCP23017 can be found there : http://ww1.microchip.com/downloads/en/D ... 21952b.pdf
Simply place pullups on RES/SDA/SCL, and attach SDA/SCL on GPIO0/GPIO2, and that is it.
Using Arduino IDE ESP framework Wire library along with Adafruit_MCP23017 library, you will be able to drive 16 GPIO outputs.