Reading Mifare RFID Tags

This tutorial explains how to read from Mifare RFID tags from your computer using a Sonmicro SM130 read/write module. The sketch below is written in Processing using my SonmicroReader library. The SM130 has a TTL serial interface that you can connect to a micocontroller, or to a personal computer through a USB-to-serial interface.  Using the latter, it’s pretty simple to send serial commands to it and receive the data back. The entire Processing sketch can be downloaded here: rfid_simple_0001.

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Sonmicro RFID Reader Library for Processing

Last year, I worked with Timo Arnall and Einar Martinussen and Jørn Knutsen on a Processing library to read and write to Mifare RFID tags using the Sonmicro SM130 read/write module.  Here it is, with a few improvements and bug fixes.

To use the library, unzip it and copy the folder to your Processing libraries folder.  Then restart Processing.  There are two example sketches, a simple reader that seeks new tags, and a full read/write example.

For more details, see the datasheet for the module. Code examples will follow in this blog.

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Here’s a quick digital clock in Processing. It also sends the time out a serial port. I use this for testing when I need for a microcontroller or other serial device to receive a string.


 Draws a digital clock in the center of the screen
 and sends the string out the serial port.

 created 7 Oct 2008
 by Tom Igoe

import processing.serial.*;

Serial myPort;    // instance of the serial library

void setup() {
  // open the applet window:
  size(300, 200);
  // initialize the font for text display:
  PFont myFont = createFont(PFont.list()[0], 24);
  // align all text center:
  // open a serial port:
  myPort = new Serial(this, Serial.list()[0], 9600);

void draw(){
  // clear the screen:
  // make a string of hour: minute:second.  Use nf()
  // to format the numbers in two digits each:
  String theTime = nf(hour(), 2) + ":" + nf(minute(), 2) + ":"+ nf(second(), 2);
  // draw it in the middle of the screen:
  text(theTime, width/2, height/2);
  // send it out the serial port:
  myPort.write(theTime + "\n");
  // wait one second before doing it again:

Sending Mail from Processing

Here’s a piece of code to send mail from Processing. It uses the net library. Warning: your mail server may not use port 25.

/* mail_client
 by Tom Igoe
  A simple mail sender client
 Created 21 January 2006

Client myClient; 
int clicks;
String reply = null;
boolean sent = false;
void setup() { 
  // Connect:
  myClient = new Client(this, "", 25); 


void draw() { 
  if(!sent) {
    myClient.write("\rHere's the body\n.\n");
  sent = true;

void waitForReply() {
  int newChar = 0;
  while (newChar != 10) {
    if(myClient.available() > 0) {
      newChar =;
      reply += (char)newChar;

RFID Reader and Image Display

This program reads ID Innovations ID-12 RFID readers and matches the tags against a list of known tags. It’s an illustration of how to use an RFID reader to associate data with a set of tags.

  RFID Reader and image display
  Language: Processing
  This program reads ID Innovations ID-12 RFID readers rom two serial ports.
  It matches the tags against a list of known tags, and uses the match to 
  associate a name with the tag.  It also scans the sketch's data directory
  to load an image associated with the name.
  Created 12 Mar 2008
  by Tom Igoe and the interaction design class at AHO, Spring 2008
  directory reading and image scanning based on an example from Marius Watts


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Reading Multiple Serial Ports in Processing

This program reads multiple serial ports and lets you know when data comes from one port or the other. The two ports in this example are attached to ID Innovations ID-12 RFID readers. The ID-12 readers send a string that ends with a byte whose value is 0x03.

   Multiple Serial Ports
   Language: Processing

   This program reads multiple serial ports and lets you know when data comes 
   from one port or the other. The two ports in this example are attached to 
   ID Innovations ID-12 RFID readers. The ID-12 readers send a string that ends 
   with a byte whose value is 0x03.
   Created 12 Mar 2008
   by Tom Igoe

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XBee Library graphing and logging application

Here’s a program that uses Rob Faludi and Dan Shiffman’s XBee library for processing to read three analog sensors from multiple remote XBee radios and graph them. It also saves the data to a comma-delimited file. It also makes sounds when the value exceeds a given threshold. For this application, you need two or more XBee series 1 radios. One is attached to the serial port of the computer, and the other is remote, broadcasting three analog values.

This also uses the ControlP5 library by Andreas Schlegel and the Ess library by Krister Olsson.

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XOR calculation for NMEA checksums (GPS protocol)

If you’ve ever seen the serial output of a GPS reader, you’ve seen a mystery string at the end like this:

That’s the checksum of the whole string. NMEA data structure for Global Positioning (GPS) readers has a checksum on the end of each sentence. The checksum is the XOR of all the bytes between the $ and the * in the sentence. For example, if the sentence is this:


then you run a checksum on this:


Here’s a Processing method to calculate the checksum, given the string between the $ and the *:

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Peak finding in Processing

In a previous example, I showed how to detect a peak in a changing analog value on a microcontroller. This example shows how to do it in Processing, assuming the microcontroller is just sending you binary values from 0 to 255. It graphs the incoming bytes, and when a peak is detected, it draws an ellipse and prints a message in the message pane.

Thanks to Matt Young for helping me debug this.

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