gistfile1.js

var stream = require('stream');

var timer = new stream.Readable({
   read: function() {
      var self = this;

      console.log('called');
      setTimeout(function() {
         self.push('ping');
         console.log('pushed');
      }, 100);
   }
});

timer.pipe(process.stdout);

setTimeout(function() {
   timer.unpipe();
}, 500);