LED Blink

Start with the “hello world” of electronics: switch a GPIO pin on and off to blink an LED.

Parts

An LED (any color)
A resistor of about 330 Ω

Strictly speaking, the resistor value should be calculated from the LED’s rated current, but around 330 Ω works for most LEDs.

Circuit

Breadboard diagram: GPIO26 goes through a 330 ohm resistor and an LED to GND

From	To
GPIO26	Resistor, then LED anode (the longer leg)
LED cathode (the shorter leg)	GND

LEDs are polarized: the longer leg is the anode and must be on the GPIO side.

Program

require 'gpio'
require 'machine'

led = GPIO.new(26, GPIO::OUT)

loop do
  led.write(1)
  Machine.delay_ms(1000)
  led.write(0)
  Machine.delay_ms(1000)
end

Every second, the program toggles the pin between 1 (HIGH) and 0 (LOW).

Run

Save the program as gpio_out.rb and put it in /home on the device (see File Transfer), then run it from the shell:

$> ./gpio_out.rb

The LED should blink once per second.