tl;dr: you can write JS code (see below) to read RFID tags with NodeJS.

Last week-end, I found my old RFID reader in a drawer. It’s a mir:ror, made by Violet, you know, the company that invented Wi-Fi rabbits. The device is a USB HID device and used to ship with a lousy app that could trigger a few predefined actions. But the company is kind of dead now and the driver is no longer available.

So, how hard would it be to write a driver that could do whatever I want? The thing is that I need it to work on OSX. And it would be great if programs could be written in JS, because it’s a language I’m comfortable with.

Being a lazy programmer, I first searched the Web for existing drivers. I found some software written in ruby and .Net. The first one expects the mir:ror to be available in /dev, which is not the case on my Mac (no idea why). The second one is for Windows obviously. Moreover, I don’t know any of these languages.

Out of luck, I wondered: is it possible to communicate with USB HID devices in NodeJS? Thirty seconds of googling later, I stumbled on this cool node extension: Node HID that does exactly what I’m looking for (you could also program keyboards, keypads, mice, etc.).

The next step was to code the driver. Hopefully, the protocol is simple and documented on this blog: http://blog.nomzit.com/2010/01/30/decoding-the-mirror-comms-protocol/.

Below is the code of the driver. It can read RFID tags, detect when the device is upside down, and disable the annoying lights and sound.

var HID = require('HID');

var devices = new HID.devices(7592, 4865);
var hid;
if (!devices.length) {
  console.log("No mir:ror found");
} else {
  hid = new HID.HID(devices[0].path);
  hid.write([03, 01]); //Disable sounds and lights
  hid.read(onRead);
}

function onRead(error, data) {
  var size;
  var id;

  //get 64 bytes
  if (data[0] != 0) {

    console.log("\n" + data.map(function (v) {return ('00' + v.toString(16)).slice(-2)}).join(','));

    switch (data[0]) {
    case 1:
      //Orientation change
      switch (data[1]) {
      case 4:
        console.log("-> mir:ror up");
        break;
      case 5:
        console.log("-> mir:ror down");
        break;
      }
      break;
    case 2:
      //RFID
      switch (data[1]) {
      case 1:
        console.log("-> RFID in");
        break;
      case 2:
        console.log("-> RFID out");
        break;
      }

      size = data[4];
      id = (data.splice(0)).splice(5, size);
      console.log(id.map(function (v) {return ('00' + v.toString(16)).slice(-2)}).join(','));
      break;
    }
  }
  hid.read(onRead);
}

Now that NodeJS can react to RFID tags, we can do all sorts of things, like switching between spaces on a Mac. Check out the video to see a demo.