nodemcu-firmware/lua_examples/mcp23008/mcp23008_buttons.lua

---
-- @description Shows how to read 8 GPIO pins/buttons via I2C with the MCP23008 I/O expander.
-- Tested on NodeMCU 0.9.5 build 20150213.
-- @circuit
--  Connect GPIO0 of the ESP8266-01 module to the SCL pin of the MCP23008.
--  Connect GPIO2 of the ESP8266-01 module to the SDA pin of the MCP23008.
--  Use 3.3V for VCC.
--  Connect switches or buttons to the GPIOs of the MCP23008 and GND.
--  Connect two 4.7k pull-up resistors on SDA and SCL
--  We will enable the internal pull up resistors for the GPIOS of the MCP23008.
-- @author Miguel (AllAboutEE)
--      GitHub: https://github.com/AllAboutEE
--      YouTube: https://www.youtube.com/user/AllAboutEE
--      Website: http://AllAboutEE.com
---------------------------------------------------------------------------------------------

local mcp23008 = require ("mcp23008")

-- ESP-01 GPIO Mapping as per GPIO Table in https://github.com/nodemcu/nodemcu-firmware
local gpio0, gpio2 = 3, 4

---
-- @name showButtons
-- @description Shows the state of each GPIO pin
-- @return void
---------------------------------------------------------
local function showButtons()

    local gpio = mcp23008.readGPIO() -- read the GPIO/buttons states

    -- get/extract the state of one pin at a time
    for pin=0,7 do

        local pinState = bit.band(bit.rshift(gpio,pin),0x1) -- extract one pin state

        -- change to string state (HIGH, LOW) instead of 1 or 0 respectively
        if(pinState == mcp23008.HIGH) then
            pinState = "HIGH"
        else
            pinState = "LOW"
        end

        print("Pin ".. pin .. ": ".. pinState)
    end
    print("\r\n")
end

do
  -- Setup the MCP23008
  mcp23008.begin(0x0,gpio2,gpio0,i2c.SLOW)

  mcp23008.writeIODIR(0xff)
  mcp23008.writeGPPU(0xff)

  tmr.create():alarm(2000, tmr.ALARM_AUTO, showButtons) -- run showButtons() every 2 seconds
end