trev/nodejs/routes/index.js

var express = require('express');
var router = express.Router();
var sucess = true;
var SerialPort = require("serialport").SerialPort
serialPort = new SerialPort("/dev/ttyACM0", {
  baudrate: 9600
}, false);

serialPort.open(function (error) {
  if ( error ) {
    sucess = false;
  } 
});

/* GET home page. */ 
router.get('/', function(req, res, next) {
  res.render('index', { title: 'Express' });
});

router.get('/toggleLight', function (req, res) {
  if(sucess) { serialPort.write(new Buffer('~','ascii')); } else {console.log("arduino not connected")}
  res.send('switch light');
});

module.exports = router;