code, circuits, & construction

When I start learning a new  platform, I have a simple rule: If you don’t know what to do with it, make pong. What I love about pong is that it’s a simple rule set, easy to understand, and implementable on just about anything with a pixel display.  You can generally implement it in a day or less on any platform. And it’s a great example of engaging interaction.  People understand what’s going on right away, and, when implemented well, it’s just challenging enough to keep you engaged for several minutes at least.  That’s good interaction, to me.

I’m a big believer in starting with the application rather than the platform.  I think you do better work when the tools serve the need rather than the other way around.  But sometimes you get stuck with the assignment to learn a particular platform or tool, and you have to make up a project on the spot.  When that happens, make pong.

As an example of this, I built pong for two platforms yesterday: an Arduino Mega with 2 8×8 LED matrices (based on my earlier post), and Processing.  Since Arduino’s programming syntax was based closely on Processing’s, I figured it should be possible to port the code from one to the other pretty quickly. It took about ten minutes to go from Arduino to Processing.  Following, I’ll describe the thought process of putting the game together for both, as a hopeful aid to beginning programmers.

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This tutorial introduces a Processing interface sketch provides a GUI for the command-line interface written into the Arduino RFID example. You should read that tutorial first. The sketch shown here also allows you to upload tags it reads to O’Reilly’s Emerging Technology Conference attendee portal, and retrieves the resulting profile. The API for this was written by Edd Dumbill. The Processing sketch retrieves RFID tags from the Arduino reader serially, then  passes the tag via a HTTP request to a PHP script on a remote server, shown below,  that adds an authorized login to the O’Reilly site.

Caveat: this tutorial was written specifically for the RFID workshop at Etech 2009.  If you’re doing this on your own, the uploader won’t work because your tags won’t be associated with records in the O’Reilly database, and the PHP script that it calls probably won’t be active on my site anymore.  But you could build your own version on your own server. The PHP code that follows below gives you a start on that process, and the Processing code below can make a HTTP call to any web address you give it.

The entire sketch can be downloaded here:

rfid_uploader_0002

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This tutorial shows how to make an Arduino-based RFID reader that reads Mifare tags and stores them in EEPROM. It is a modification of Alex Zivanovic’s code on Tinker.it. Thanks to Alex and Massimo Banzi for the reference. Once you’ve got it running, go on to the RFID to Web example, which provides a Processing interface sketch provides a GUI for the command-line interface written into the Arduino code.

The entire sketch can be downloaded here:

arduino_rfid_reader_0001

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Mifare RFID tags, like other RFID tags, contain a serial number that can be read using an RFID reader, but they also have a limited amount of memory space that you can write data to, and read back from.  This can be handy if you want to do something like keep a user’s account balance or name directly on the RFID tag.

This tutorial shows a number of the functions of my sonMicroReader  library for Processing, including how to write to the memory on tags.  It uses the same circuit as the SM130 reader example. The entire sketch can be downloaded here:

sonmicro_writer_0001

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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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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.

SonMicroReader.zip

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.

/*
  Clock

 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);
  textFont(myFont);
  // align all text center:
  textAlign(CENTER);
  // open a serial port:
  myPort = new Serial(this, Serial.list()[0], 9600);
}

void draw(){
  // clear the screen:
  background(0);
  // 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:
  delay(1000);
}

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
 */

import processing.net.*;
Client myClient;
int clicks;
String reply = null;
boolean sent = false;
void setup() {
  // Connect:
  myClient = new Client(this, "echonyc.com", 25);
  delay(300);

} 

void draw() {
  if(!sent) {
    waitForReply();
    myClient.write("HELO echonyc.com\n");
    waitForReply();
    myClient.write("MAIL FROM:tigoe@echonyc.com\n");
    waitForReply();
    myClient.write("RCPT TO:tigoe@echonyc.com\n");
    waitForReply();
    myClient.write("DATA\n");
    waitForReply();
    myClient.write("Subject:Noodles\n");
    myClient.write("From:tigoe@echonyc.com\n");
    myClient.write("To:tigoe@tigoe.net\n");
    myClient.write("\rHere's the body\n.\n");
    waitForReply();
    myClient.write("QUIT\n\r");
    waitForReply();
  }
  sent = true;
} 

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

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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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 0×03.

/*
   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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