Arduino code making an HTTP request to Google Analytics and returning the status code. Replace `YOURGAID-HERE` by your GA tag.

PrismCarpet.ino

#include <SPI.h>
#include <Ethernet.h>

// Thx http://bildr.org/2012/11/force-sensitive-resistor-arduino/
// Make use of https://developers.google.com/analytics/devguides/collection/protocol/v1/devguide

// MAC Address, needed by the Ethernet Shield
byte mac[]     = {  0xB0, 0xC0, 0xDE, 0xEF, 0xFE, 0xC7 };

int  pin_red   = 7; // Red LED
int  pin_green = 8; // Green LED
int  pin_FSR   = A0; // Force sensor pin
int  pin_POT   = A1; // Potentiometer pin

// To skip the DNS
IPAddress server(173,194,40,97); // www.google-analytics.com => 173.194.40.97
EthernetClient client;

// Global switch (debug mode without API call)
boolean netword_enabled = true;

/**
 * Perform an HTTP request to Google Analytics
 * 
 * @return int  The HTTP response code
 */
int sendEventToGA() {
  int responseCode      = 0;
  
  if (!netword_enabled) {
    return responseCode;  
  }
  
  // open the connection
  if (client.connect(server, 80)) {
    int responseSize      = 0;
    int responseSizeMax   = 1024;
    char response[1024];
    String eventData = "v=1&tid=YOURGAID-HERE&cid=1337&t=event&ec=irl&ea=visitor&el=IRL Visit&ev=1"; // Refer to the Google documentation
    
    Serial.println("Connection opened!");

    // Write the HTTP request to the Client    
    client.println("POST /collect HTTP/1.1");
    client.println("Host: www.google-analytics.com");
    client.print("Content-Length: ");
    client.println(eventData.length());
    client.println("Content-Type:application/x-www-form-urlencoded");
    client.println();
    client.println(eventData);
    
    Serial.println("Request sent.");
    
    // Wait a little bit
    delay(1000);
    
    // Read the response, looking for the Response Code.
    while (client.available() && client.connected() && responseCode < 100 && responseSize < responseSizeMax) {   
      
      response[responseSize] = client.read();
      responseSize++;
      response[responseSize] = '\0'; // Set manualy the end of string char
      
      // Here is the magic!
      sscanf (response, "HTTP/1.%*d %d", &responseCode);
      
      Serial.print("HTTP code ");
      Serial.print(responseCode);
      Serial.print(" founded in ");
      Serial.println(response);
    }
  }
  
  Serial.println("End of communications.");
  
  client.stop();
  return responseCode;
}

void setup() {
  // Open serial communications and wait for port to open:
  Serial.begin(9600);
  
  pinMode(pin_red, OUTPUT);
  pinMode(pin_green, OUTPUT);
  
  // Turn off the lights
  digitalWrite(pin_green, LOW);
  digitalWrite(pin_red, LOW);

  // start the Ethernet connection
  if (netword_enabled && Ethernet.begin(mac) == 0) {
    Serial.println("Failed to configure Ethernet using DHCP");
    digitalWrite(pin_red, HIGH);
    
    // no point in carrying on, so do nothing forevermore:
    for(;;)
      ;
  }
  
  // give the Ethernet shield a second to initialize:
  delay(1000);
}

void loop()
{
  int FSRReading = analogRead(pin_FSR); 
  int threshold  = analogRead(pin_POT);
  int responseCode;
  
  // If the pressure is higher than the setted threshold, call the API
  if (FSRReading > threshold) {
    digitalWrite(pin_green, HIGH);
    
    responseCode = sendEventToGA();
    
    if (responseCode >= 200 && responseCode < 400) {
      digitalWrite(pin_green, HIGH);
      digitalWrite(pin_red, LOW);
    } else {
      digitalWrite(pin_green, LOW);
      digitalWrite(pin_red, HIGH);
      Serial.print("Something went wrong, API replied: ");
      Serial.println(responseCode);
    }
  }
  
  Serial.print("Pressure: ");  
  Serial.print(FSRReading);
  Serial.print(" - Potentiometer: ");  
  Serial.println(threshold);
  delay(500);
  
  digitalWrite(pin_green, LOW);
  digitalWrite(pin_red, LOW);
}