Monitoring message queues with Arduino

Alex Kane — Wed, 09 Dec 2009 14:53:34 +0000

This is a gadget I made to tell me at a glance the size of the various message queues that I manage at TuneCore. It sits on my desk next to my monitor and tells me right away what's going on with our delivery system. A steady light means the queue is not very long; a rapidly blinking light means that the number of items in the queue is very large and it needs attention.

I built it over a weekend using an Arduino microcontroller with an Ethernet shield. It requests the queue sizes from a web server once a minute.

Parsing an HTTP Response

Here's an example of an HTTP response that I have to parse in order to get the values I'm looking for:
Buffer: HTTP/1.1 200 OK Buffer: Date: Tue, 08 Dec 2009 14:15:34 GMT Buffer: Server: Apache/2.2.3 (CentOS) Buffer: Last-Modified: Tue, 08 Dec 2009 14:15:02 GMT Buffer: ETag: "fc117-28-332a2580" Buffer: Accept-Ranges: bytes Buffer: Content-Length: 40 Buffer: Connection: close Buffer: Content-Type: text/plain; charset=UTF-8 Buffer: Buffer: queue_sizes Buffer: 0 Buffer: 0 Buffer: 0 Buffer: 0 Buffer: 0 Buffer: 0 Buffer: 0 Buffer: 1 Buffer: 0 Buffer: 0 Buffer: 0 Buffer: 0 Buffer: 0 Buffer: 0
It turns out that there's a lot of libraries for setting the Arduino Ethernet shield up as a server but I couldn't find any that make it easy to parse a response.

There were two major hurdles in the design of the program. One was how to parse the HTTP response. It took some thought (and Googling) but what you have to do is build string buffers as you read the the response one character at a time. Then process the buffer to determine if your looking at the HTTP header or the actual data that you've served.

The other programming problem was getting the lights to blink independently of one another. It was a difficult because the Arduino only does one thing at a time. I was able to accomplish this using the Metronome library, although there is still some blocking going on when the lights blink. I believe the solution will be to remove the delay() statements in the blink code.

This is the first time I've felt that a project is worthy of mounting in a project box. I got all the LEDs, mounts and box from Radio Shack, and bought a Dremel and label maker at Target. The next few hours were spent cursing and carving the plastic and soldering everything together.

More pictures

The code

Here's the code that make this thing tick:

#include 
#include 
#include 
 
#define MAX_STRING_LEN  20
#define BLINK_DELAY 100
#define LED_INTERVAL 60000
 
#define AMAZON_LED 2 // Define the led's pin
#define AMAZONOD_LED 3
#define NOKIA_LED 4
#define ITUNES_LED 5
#define LIMEWIRE_LED 6
#define RHAPSODY_LED 7
#define NAPSTER_LED 8
#define LALA_LED 9
 
int amazon_q;
int amazonod_q;
int amiestreet_q;
int emusic_q;
int groupietunes_q;
int itunes_q;
int lala_q;
int limewire_q;
int napster_q;
int nokia_q;
int rhapsody_q;
int shockhound_q;
int streaming_q;
 
Metro queueCheckMetro = Metro(10000);
 
Metro amazonMetro = Metro(1000);
Metro amazonodMetro = Metro(1000);
Metro nokiaMetro = Metro(1000);
Metro itunesMetro = Metro(1000);
Metro limewireMetro = Metro(1000);
Metro rhapsodyMetro = Metro(1000);
Metro napsterMetro = Metro(1000);
Metro lalaMetro = Metro(1000);
 
int state = HIGH;
 
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
byte ip[] = { 192, 168, 2, 2 };
byte gateway[] = { 192, 168, 2, 1 };
byte subnet[] = { 255, 255, 255, 0 };
byte server[] = { 0,0,0,0 }; // Put the server's IP address here
Client client(server, 80);
int data_index = 0;
boolean header = true;
String buffer = String(100);
int response_writeindex = 0;
 
void setup()
{
 
  pinMode(AMAZON_LED,OUTPUT);
  digitalWrite(AMAZON_LED,state);
  pinMode(AMAZONOD_LED,OUTPUT);
  digitalWrite(AMAZONOD_LED,state);
  pinMode(NOKIA_LED,OUTPUT);
  digitalWrite(NOKIA_LED,state);
  pinMode(ITUNES_LED,OUTPUT);
  digitalWrite(ITUNES_LED,state);
  pinMode(LIMEWIRE_LED,OUTPUT);
  digitalWrite(LIMEWIRE_LED,state);
  pinMode(RHAPSODY_LED,OUTPUT);
  digitalWrite(RHAPSODY_LED,state);
  pinMode(NAPSTER_LED,OUTPUT);
  digitalWrite(NAPSTER_LED,state);
  pinMode(LALA_LED,OUTPUT);
  digitalWrite(LALA_LED,state);
 
  Ethernet.begin(mac, ip, gateway, subnet);
  Serial.begin(9600);
 
  delay(1000);
 
  Serial.println("connecting...");
 
  if (client.connect()) {
    Serial.println("connected");
    client.println("GET /queue_size.txt HTTP/1.0");
    client.println();
  } else {
    Serial.println("connection failed");
  }
}
 
void loop()
{ 
 
  if(queueCheckMetro.check() == 1){
   checkQueues();
 }
 
  blinkLEDS();
}
 
void checkQueues(){
  queueCheckMetro.interval(60000); // check the queues once a minute
 while (client.available()) {
    serialEvent();
  }
 
  calculateBlinkRates();
 
  if (!client.connected()) {
    Serial.println();
    Serial.println("Disconnected");
    client.stop();
 
     if (client.connect()) {
      client.println("GET /queue_size.txt HTTP/1.0");
      client.println();
      delay(2000);
    } else {
      Serial.println("Reconnect failed");
    }
  }
}
 
void serialEvent(){
  char inChar = client.read();
 
  if(inChar != '\n'){
   buffer.append(inChar);
  } else {
    Serial.print("Buffer: ");
    Serial.println(buffer);
    if(buffer.contains("queue_sizes")){
      // Finished reading HTTP header
      header = false;
    }
 
    if(header == false){
      parse_data_buffer();
      data_index = data_index++;
    }
    buffer = "";
  }
 
}
 
void parse_data_buffer(){
  // Parse the line
  switch (data_index){
          case 3:
            amazon_q = atoi(buffer);
            break;
          case 4:
            amazonod_q = atoi(buffer);
            break;
          case 5:
            amiestreet_q = atoi(buffer);
            break;
          case 6:
            emusic_q = atoi(buffer);
            break;
          case 7:
            groupietunes_q = atoi(buffer);
            break;
          case 8:
            itunes_q = atoi(buffer);
            break;
          case 9:
            lala_q = atoi(buffer);
            break;
          case 10:
            limewire_q = atoi(buffer);
            break;
          case 11:
            napster_q = atoi(buffer);
            break;
          case 12:
            nokia_q = atoi(buffer);
            break;
          case 13:
            rhapsody_q = atoi(buffer);
            break;
          case 14:
            shockhound_q = atoi(buffer);
            break;
          case 15:
            streaming_q = atoi(buffer);
            break;
        }
        return;
  }
 
void calculateBlinkRates(){
  if(amazon_q == 0){
    amazon_q=1;
  }
  if(amazonod_q == 0){
    amazonod_q=1;
  }
  if(nokia_q == 0){
    nokia_q=1;
  }
  if(itunes_q == 0){
    itunes_q=1;
  }
  if(limewire_q == 0){
    limewire_q=1;
  }
  if(rhapsody_q == 0){
    rhapsody_q=1;
  }
  if(napster_q == 0){
    napster_q=1;
  }
  if(lala_q == 0){
    lala_q=1;
  }
  int amazon_on_for = LED_INTERVAL / amazon_q;
  int amazonod_on_for = LED_INTERVAL / amazon_q;
  int nokia_on_for = LED_INTERVAL / nokia_q;
  int itunes_on_for = LED_INTERVAL / itunes_q;
  int limewire_on_for = LED_INTERVAL / limewire_q;
  int rhapsody_on_for = LED_INTERVAL / rhapsody_q;
  int napster_on_for = LED_INTERVAL / napster_q;
  int lala_on_for = LED_INTERVAL / lala_q;
  amazonMetro.interval(amazon_on_for);
  amazonodMetro.interval(amazon_on_for);
  nokiaMetro.interval(nokia_on_for);
  itunesMetro.interval(itunes_on_for);
  limewireMetro.interval(limewire_on_for);
  rhapsodyMetro.interval(rhapsody_on_for);
  napsterMetro.interval(napster_on_for);
  lalaMetro.interval(lala_on_for);
}
 
void blinkLEDS(){
 if (amazonMetro.check() == 1) { // check if the metro has passed it's interval .
    blinkLED(AMAZON_LED);
  }
 if (amazonodMetro.check() == 1) { // check if the metro has passed it's interval .
    blinkLED(AMAZONOD_LED);
  }
 if (nokiaMetro.check() == 1) { // check if the metro has passed it's interval .
    blinkLED(NOKIA_LED);
  }
 if (itunesMetro.check() == 1) { // check if the metro has passed it's interval .
    blinkLED(ITUNES_LED);
  }
 if (limewireMetro.check() == 1) { // check if the metro has passed it's interval .
    blinkLED(LIMEWIRE_LED);
  }
 if (rhapsodyMetro.check() == 1) { // check if the metro has passed it's interval .
    blinkLED(RHAPSODY_LED);
 }
 if (napsterMetro.check() == 1) { // check if the metro has passed it's interval .
    blinkLED(NAPSTER_LED);
 }
 if (lalaMetro.check() == 1) { // check if the metro has passed it's interval .
    blinkLED(LALA_LED);
 }
}
 
void delayWithBlink(int delay){
 for(int i=0; i &lt;= delay; i++){
  blinkLEDS();
 }
}
 
void blinkLED(int pin){
  digitalWrite(pin, LOW);
  delay(BLINK_DELAY);
  digitalWrite(pin,HIGH);
}

Robot is Happy » ethernet shield

Monitoring message queues with Arduino

Parsing an HTTP Response

More pictures

The code