pinMode()

Configures the specified pin to behave either as an input or an output

• Syntax:
  

  pinMode(pin, mode)

• Example1: Set GPIO 20 as input)
  

  pinMode(20, INPUT)

• Example2: Set GPIO 20 as output)
  

  pinMode(20, OUTPUT)

digitalWrite()

Write a HIGH or a LOW value to a pin.

• Syntax:
  

  digitalWrite(pin, value)

• Example1: Set GPIO 20 to low
  

  digitalWrite(20, LOW)

• Example2: Set GPIO 20 to high
  

  digitalWrite(20, HIGH)

digitalRead()

Reads the value from a specified pin, either HIGH or LOW.

• Syntax:
  

  digitalRead(pin)

• Example: Read value from GPIO 20, return high or low
  

  digitalRead(20)

delay()

Pauses the program for the amount of time (in seconds)

• Syntax:
  

  delay(second)

• Example: Delay 0.5 second
  

  delay(0.5)

pin_direction_status()

 Chcek the direction of a give pin

• Syntax:
  

  pin_direction_status(pin)

• Example: Check the direction of pin20, return o if it is declared as output, return i if it is declared as input, otherwise return nothing ("")
  

  pin_direction_status(20)

Default Configuration

This is the pin layout for GL.iNet wireless router, you can change its value to match with your hardware configuration.

GPIO = {20, 19, 18, 22, 21}

Example

Example below is a Lua script running on OpenWRT which turn on GPIO 20, it then turn off after 0.5 second

#!/usr/bin/lua
require "gpio" --import lua_gpio library
IO_pin=20 -- or IO_pin=GPIO[1]
pinMode(IO_pin,OUTPUT) -- configure IO_pin as output
digitalWrite(IO_pin, HIGH) -- turn it ON
print(digitalRead(IO_pin)) -- print the output
delay(0.5) -- wait for 0.5 second
digitalWrite(IO_pin, LOW) -- turn it OFF
print(digitalRead(IO_pin)) -- print the output

Another Example

#!/usr/bin/lua
require "gpio"
 
----- set GPIO as output
for i=1, 5 do
  pinMode(GPIO[i],OUTPUT)
end
 
----- set GPIO to HIGH
for i=1, 5 do
  digitalWrite(GPIO[i],HIGH)
  delay(0.2)
end
 
----- set GPIO to LOW
for i=1, 5 do
  digitalWrite(GPIO[i],LOW)
  delay(0.2)
end

Download

Lua_GPIO source code is available here.

Related articles

Lua_ShiftOut: A 74HC595 Shift Register Library for Lua

Resources

http://wiki.openwrt.org/doc/hardware/port.gpio