树莓派与node.js —— onoff、dht

1. 发光二极管

tm-onoff

var Gpio = require('tm-onoff').Gpio,
    led = new Gpio(17, 'out'),
    button = new Gpio(18, 'in', 'both');
         // 'both'：按钮的上升下降沿都应该被处理，即调用如下的函数
button.watch(function(err, value) {
    led.writeSync(value);
});

上述代码在ctrl+c退出时，并未释放资源，也未处理错误，一份更完整的处理如下：

var Gpio = require('tm-onoff').Gpio,
    led = new Gpio(17, 'out'),
    button = new Gpio(18, 'in', 'both');

button.watch(function(err, value) {
    if (err) exit();
    led.writeSync(value);
});

function exit() {
    led.unexport();
    button.unexport();
    process.exit();
}

process.on('SIGINT', exit);

• 通过调用 led、btn 的 unexport 方法以释放其资源；

  var onoff = require('onoff');
  var Gpio = onoff.Gpio,
      led = new Gpio(4, 'out'),
      interval;
  
  interval = setInterval(function () { //#C
      var value = (led.readSync() + 1) % 2; //#D
      led.write(value, function () { //#E
          console.log("Changed LED state to: " + value);
      });
  }, 2000);
  
  process.on('SIGINT', function () { //#F
      clearInterval(interval);
      led.writeSync(0); //#G
      led.unexport();
      console.log('Bye, bye!');
      process.exit();
  });

2. dht：温湿度传感器

GitHub - momenso/node-dht-sensor: Node.js Humidity and Temperature sensor addon

• node-dht-sensor 的安装使用如下命令：

  $ npm install --save node-dht-sensor
  
  # 如果存在权限问题，使用
  
  $ sudo npm install --unsafe-perm --save node-dht-sensor

var dhtLib = require('node-dht-sensor');
dhtLib.initialize(11, 12);      
    // 第一个参数表示传感器类型，dht11使用11，dht22使用22
    // 第二个参数表示GPIO引脚号
var interval = setInterval(function (){
    read();
}, 2000);
function read() {
    var readout = dhtLib.read();
    console.log('Temperature: ' + readout.temperature.toFixed(2) + 'C, ' + 
        'humidity: ' + readout.humidity.toFixed(2) + '%');
};
process.on('SIGINT', function () {
    clearInterval(interval);
    console.log('Bye, bye!');
    process.exit();
});