diff --git a/lua_modules/mcp23017/mcp23017.lua b/lua_modules/mcp23017/mcp23017.lua
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+++ b/lua_modules/mcp23017/mcp23017.lua
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+---
+-- @description Expands the ESP8266's GPIO to 8 more I/O pins via I2C with the MCP23017 I/O Expander
+-- MCP23017 Datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/21919e.pdf
+-- Tested on NodeMCU 0.9.5 build 20150213.
+-- @date March 02, 2015
+-- @author Miguel 
+--  GitHub: https://github.com/AllAboutEE 
+--  YouTube: https://www.youtube.com/user/AllAboutEE
+--  Website: http://AllAboutEE.com
+--------------------------------------------------------------------------------
+
+local moduleName = ... 
+local M = {}
+_G[moduleName] = M 
+
+-- Constant device address.
+local MCP23017_ADDRESS = 0x20
+
+-- These address are valid for IOCON.BANK = 0
+-- Do not change IOCON.BANK
+
+local MCP23017_IODIRA = 0x00
+local MCP23017_IODIRB = 0x1
+local MCP23017_IPOLA = 0x02
+local MCP23017_IPOLB = 0x03
+local MCP23017_GPINTENA = 0x04
+local MCP23017_GPINTENB = 0x05
+local MCP23017_DEFVALA = 0x06
+local MCP23017_DEFVALB = 0x07
+local MCP23017_INTCONA = 0x08
+local MCP23017_INTCONB = 0x09
+local MCP23017_IOCON = 0x0A
+local MCP23017_IOCON = 0x0B
+local MCP23017_GPPUA = 0x0C
+local MCP23017_GPPUB = 0x0D
+local MCP23017_INTFA = 0x0E
+local MCP23017_INTFB = 0x0F
+local MCP23017_INTCAPA = 0x10
+local MCP23017_INTCAPB = 0x11
+local MCP23017_GPIOA = 0x12
+local MCP23017_GPIOB = 0x13
+local MCP23017_OLATA = 0x14
+local MCP23017_OLATB = 0x15
+
+-- Default value for i2c communication
+local id = 0
+
+-- pin modes for I/O direction
+M.INPUT = 1
+M.OUTPUT = 0
+
+-- pin states for I/O i.e. on/off
+M.HIGH = 1
+M.LOW = 0
+
+-- Weak pull-up resistor state
+M.ENABLE = 1
+M.DISABLE = 0
+
+
+---
+-- @name write
+-- @description Writes one byte to a register
+-- @param registerAddress The register where we'll write data
+-- @param data The data to write to the register
+-- @return void
+----------------------------------------------------------
+local function write(registerAddress, data)
+    i2c.start(id)
+    i2c.address(id,MCP23017_ADDRESS,i2c.TRANSMITTER) -- send MCP's address and write bit
+    i2c.write(id,registerAddress)
+    i2c.write(id,data)
+    i2c.stop(id)
+end
+
+---
+-- @name read
+-- @description Reads the value of a regsiter
+-- @param registerAddress The reigster address from which to read
+-- @return The byte stored in the register
+----------------------------------------------------------
+local function read(registerAddress)
+    -- Tell the MCP which register you want to read from
+    i2c.start(id)
+    i2c.address(id,MCP23017_ADDRESS,i2c.TRANSMITTER) -- send MCP's address and write bit
+    i2c.write(id,registerAddress)
+    i2c.stop(id)
+    i2c.start(id)
+    -- Read the data form the register
+    i2c.address(id,MCP23017_ADDRESS,i2c.RECEIVER) -- send the MCP's address and read bit
+    local data = 0x00
+    data = i2c.read(id,1) -- we expect only one byte of data
+    i2c.stop(id)
+
+    return string.byte(data) -- i2c.read returns a string so we convert to it's int value
+end
+
+---
+--! @name begin
+--! @description Sets the MCP23017 device address's last three bits. 
+--  Note: The address is defined as binary 0100[A2][A1][A0] where 
+--  A2, A1, and A0 are defined by the connection of the pins, 
+--  e.g. if the pins are connected all to GND then the paramter address 
+--  will need to be 0x0.
+-- @param address The 3 least significant bits (LSB) of the address
+-- @param pinSDA The pin to use for SDA
+-- @param pinSCL The pin to use for SCL
+-- @param speed The speed of the I2C signal
+-- @return void
+---------------------------------------------------------------------------
+function M.begin(address,pinSDA,pinSCL,speed)
+ MCP23017_ADDRESS = bit.bor(MCP23017_ADDRESS,address)
+ i2c.setup(id,pinSDA,pinSCL,speed)
+end
+
+---
+-- @name writeGPIO
+-- @description Writes a byte of data to the GPIO register
+-- @param dataByte The byte of data to write
+-- @return void
+----------------------------------------------------------
+function M.writeGPIOA(dataByte)
+    write(MCP23017_GPIOA,dataByte)
+end
+
+function M.writeGPIOB(dataByte)
+    write(MCP23017_GPIOB,dataByte)
+end
+
+---
+-- @name readGPIO
+-- @description reads a byte of data from the GPIO register
+-- @return One byte of data
+----------------------------------------------------------
+function M.readGPIOA()
+    return read(MCP23017_GPIOA)
+end
+
+function M.readGPIOB()
+    return read(MCP23017_GPIOB)
+end
+
+---
+-- @name writeIODIR
+-- @description Writes one byte of data to the IODIR register
+-- @param dataByte The byte of data to write
+-- @return void
+----------------------------------------------------------
+function M.writeIODIRA(dataByte)
+    write(MCP23017_IODIRA,dataByte)
+end
+
+function M.writeIODIRB(dataByte)
+    write(MCP23017_IODIRB,dataByte)
+end
+
+---
+-- @name readIODIR
+-- @description Reads a byte from the IODIR register
+-- @return The byte of data in IODIR
+----------------------------------------------------------
+function M.readIODIRA()
+    return read(MCP23017_IODIRA)
+end
+
+function M.readIODIRB()
+    return read(MCP23017_IODIRB)
+end
+
+---
+-- @name writeGPPU The byte to write to the GPPU
+-- @description Writes a byte of data to the 
+-- PULL-UP RESISTOR CONFIGURATION (GPPU)REGISTER 
+-- @param databyte the value to write to the GPPU register.
+-- each bit in this byte is assigned to an individual GPIO pin
+-- @return void
+----------------------------------------------------------------
+function M.writeGPPUA(dataByte)
+    write(MCP23017_GPPUA,dataByte)
+end
+
+function M.writeGPPUB(dataByte)
+    write(MCP23017_GPPUB,dataByte)
+end
+
+---
+-- @name readGPPU
+-- @description Reads the GPPU (Pull-UP resistors register) byte
+-- @return The GPPU byte i.e. state of all internal pull-up resistors
+-------------------------------------------------------------------
+function M.readGPPUA()
+    return read(MCP23017_GPPUA)
+end
+
+function M.readGPPUB()
+    return read(MCP23017_GPPUB)
+end
+
+return M