Handle 3 electrodes

The code should be able to handle 3 electrodes for R, G and B. Didn't
test it so far (need 2 other electrodes).

color.py

@@ -3,49 +3,71 @@
 import serial
 import pygame
 
+
+def compute_value(line, minimum, maximum):
+    line = line.split(" ")
+    if len(line) < 3:
+        return False
+
+    for i in range(3):
+        value[i] = int(255*(line[i]-minimum[i])/(maximum[i]-minimum[i]))
+        if value[i] > 255:
+            value[i] = 255
+        elif value[i] < 0:
+            value[i] = 0
+
+    return value[0], value[1], value[2]
+
+
 ser = serial.Serial("/dev/ttyACM0", 115200)
 pygame.init()
 
 size = width, height = 640, 480
 screen = pygame.display.set_mode(size)
+pygame.display.set_caption("Touchless 3D tracking")
 screen.fill((0, 0, 0))
 
 try:
     ser.open()
-except Exception:
-    print("Error while opening serial port.")
+except Exception as e:
+    print("Error while opening serial port : "+str(e))
 
 if ser.isOpen():
     try:
         ser.flushInput()
         ser.flushOutput()
 
-        maximum = -1
-        minimum = -1
+        maximum = [-1, -1, -1]
+        minimum = [-1, -1, -1]
 
         print("Calibration :")
         pygame.display.flip()
 
-        for i in range(50) :
+        for i in range(50):
             line = float(ser.readline())
 
             if line < minimum or minimum < 0:
-                minimum = line
-                if line > maximum:
-                    maximum = line
+                minimumR = line
+            if line > maximum:
+                maximumR = line
 
         print("Go :")
-        while True:
+        running = True
+        while running:
+            # Quit if window is closed
+            for event in pygame.event.get():
+                if event.type == pygame.QUIT:
+                    running = False
+
+            # Read line from serial
             line = float(ser.readline())
-            valueR = int(255*(line-minimum)/(maximum-minimum))
-            if valueR < 0:
-                valueR = 0
-            if valueR > 255:
-                valueR = 255
+            # Compute the value for red
+            value = compute_value(line, minimum, maximum)
 
-            screen.fill((valueR, 0, 0))
-            pygame.display.flip()
+            if value is not False:
+                screen.fill(value)
+                pygame.display.flip()
 
         ser.close()
-    except Exception:
-        print("Error while fetching data from serial.")
+    except Exception as e:
+        print("Error while fetching data from serial : "+str(e))

touchless_tracking/touchless_tracking.ino

-#define resolution 8
-#define mains 50 // 60: north america, japan; 50: most other places
+/* Touchless tracking
+ * ==================
+ * This code takes as many measurements as it can at approximately
+ * 10Hz = 60 Hz / (2 full cycles * 3 sensors).
+ *
+ * The code takes as many measurements as possible on the period of two
+ * cycles of the main power frequency, in order to cancel out any potential
+ * coupling.
+ *
+ * Original code was found on instructables :
+ * http://www.instructables.com/id/DIY-3D-Controller/
+ *
+ * Code slightly modified and commented by Phyks for HackENS
+ *
+ * As I found the code on Instructables and I don't give a damn to the 
+ * modifications I made, you may reuse it freely by writing where you 
+ * found it.
+ */
 
+#define resolution 8
+// Frequency of main power to avoid coupling
+#define mains 50
+// Time between measures
 #define refresh 2 * 1000000 / mains
 
+// Pins to use
+// Must be between 8 and 13 to use this code without 
+// modifications (PORTB is for pins 8 to 13)
+//
+// Note : If you change pin numbers, you *must* change the mask.
+//        See arduino doc for more info.
+#define PIN_R 8
+#define MASK_R B00000001
+#define PIN_G 9
+#define MASK_G B00000010
+#define PIN_B 10
+#define MASK_B B00000100
+
 // Counter for the timer
 extern volatile unsigned long timer0_overflow_count;
 
-/* === */
-/* ??? */
 void startTimer() {
     timer0_overflow_count = 0;
-    TCNT0 = 0;
+    TCNT0 = 0; // Initialize counter value to 0
 }
 
 unsigned long checkTimer() {
@@ -19,40 +50,51 @@ unsigned long checkTimer() {
 
 long time(int pin, byte mask) {
     unsigned long count = 0, total = 0;
-    
+
     while(checkTimer() < refresh) {
-        // pinMode is about 6 times slower than assigning
+        // Note : pinMode is about 6 times slower than assigning
         // DDRB directly, but that pause is important
+
+        // Set pin as output and LOW, see arduino doc for info on PORTB
         pinMode(pin, OUTPUT);
         PORTB = 0;
-        
+
+        // Set it as INPUT to take measure
         pinMode(pin, INPUT);
-        
+
+        // While PINB is low, increment counter
         while((PINB & mask) == 0)
             count++;
-            
+
         total++;
     }
+    // Restart timer for next measurement
     startTimer();
+    // Return the measurement result
     return (count << resolution) / total;
 }
 
-/* ??? */
-/* === */
-
 void setup() {
     // Initialize serial communication
     Serial.begin(115200);
-    
-    // INPUT on pin 8
-    pinMode(8, INPUT);
-    
+
+    // INPUT on pins
+    pinMode(PIN_R, INPUT);
+    pinMode(PIN_G, INPUT);
+    pinMode(PIN_B, INPUT);
+
     // Start timer
     startTimer();
 }
 
 void loop() {
     // Print output to serial in decimal
-    Serial.print(time(8, B00000001), DEC);
+    Serial.print(time(PIN_R, MASK_R), DEC);
     Serial.print(" ");
+
+    Serial.print(time(PIN_G, MASK_G), DEC);
+    Serial.print(" ");
+
+    Serial.print(time(PIN_B, MASK_B), DEC);
+    Serial.print("\n");
 }