Added Michael Shiloh's WifiSignalStrengthIndicator example

hardware/arduino/avr/libraries/Bridge/examples/WifiSignalStrengthIndicator/WifiSignalStrengthIndicator.ino

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+/*
+ Wifi Signal Strength Indicator
+ 
+ This example demonstrates the use of the bridge and process libraries 
+ to communicate between the Arduino side and the linux side of the Arduino Yun. 
+ 
+ The Linux script returns the strength of the wifi signal.
+ 
+ The Arduino sketch uses LEDs to indicate whether the current value of 
+ the signal strength is above, below, or the same as the last value 
+ 
+ The circuit: 
+ * LEDs on pins 8, 9, and 10
+ * Built-in LED on pin 13
+ 
+ The script:
+ The following one line script must exist in the /root directory of the 
+ linux file system, in a file named "wifiStrength.sh", and it must be executable:
+ 
+ tail -1 /proc/net/wireless | cut  -c22-23
+ 
+ created 06 June 2013
+ by Michael Shiloh
+ modified 08 June 2013
+ by Tom Igoe
+ 
+ This example code is in the public domain
+ 
+ */
+
+
+#include <Process.h>
+
+// global variable to store the last value of the signal strength
+int lastValue;
+
+void setup() {
+  // set up LED pins as outputs:
+  pinMode(8, OUTPUT);
+  pinMode(9, OUTPUT);
+  pinMode(10, OUTPUT);
+  pinMode(13,OUTPUT);
+
+  // Indicate that you're ready by flashing pin 13 LED twice
+  for (int flash = 0; flash < 3; flash++) {
+    digitalWrite(13,HIGH);
+    delay(200);
+    digitalWrite(13,LOW);
+    delay(800);
+  }
+  // initialize Serial and Bridge:
+  Serial.begin(9600);
+  Bridge.begin();
+
+  // Indicate that setup is finished
+  digitalWrite(13,HIGH);
+}
+
+void loop() {
+  int value = 0;      // the signal strength as an integer
+  String result;      // the result of the process as a String
+  Process wifiCheck;  // the process itself
+
+
+  // Run the script on the linux side. Note that any word 
+  //or text separated by a tab or space is considered 
+  //an additional parameter:
+  wifiCheck.begin("ash");
+  wifiCheck.addParameter("/root/wifiStrength.sh");
+  wifiCheck.run();
+
+  // If the process has sent any characters:
+  while (wifiCheck.available()>0) {
+    result = wifiCheck.readString(); // read the result into a string
+    value = result.toInt();  // parse the string as an int
+  }
+
+  //  for debugging
+  Serial.print("previous strength:");  
+  Serial.print(lastValue);
+  Serial.print("\tcurrent strength:");  
+  Serial.println(value);
+
+  // indicate the relative string by lighting the appropriate LED
+  allOff();      // turn off all the LEDS
+
+  if (value > lastValue) {     // if the signal's getting stronger
+    digitalWrite(10, HIGH);
+  }
+  else if (value < lastValue){ // if the signal's getting weaker
+    digitalWrite(8, HIGH);
+  }
+  else {                       // if the signal's stayed steady
+    digitalWrite(9, HIGH);
+  }
+
+  lastValue = value; // record this value for next time
+  delay(10);      // small delay before next time through the loop
+}
+
+
+void allOff() {
+  digitalWrite(8, LOW);
+  digitalWrite(9, LOW);
+  digitalWrite(10, LOW); 
+}
+
+
+
+
+
+