text: var Gpio = require('onoff').Gpio,
      rled = new Gpio(17, 'out'),
      bled = new Gpio(22, 'out'),
      gled = new Gpio(27, 'out');
  
  
  function blink(led, frequency, duration){
    var iv = setInterval(function(){
      led.writeSync(led.readSync() === 0 ? 1 : 0);
    }, frequency);
  
    setTimeout(function() {
      clearInterval(iv); // Stop blinking
      led.writeSync(0);  // Turn LED off.
      led.unexport();    // Unexport GPIO and free resources
    }, duration);
  }
  
  blink(rled, 250, 20000);
  blink(bled, 500, 20000);
  blink(gled, 1000, 20000);
  