diff --git a/circuitpython/code/main.py b/circuitpython/code/main.py
index b08dd47..883c0dd 100644
--- a/circuitpython/code/main.py
+++ b/circuitpython/code/main.py
@@ -33,15 +33,14 @@ __version__ = 0.2
 ##########
 # config #
 ##########
-print_data = True
-send_json_data = True
-backup_data = True
-data_to_neopixel = True
-gps_enable = True
-update_interval = const(10)   # in seconds
-send_json_data = True
-datetime_format = "{:04}/{:02}/{:02}_{:02}:{:02}:{:02}"
-neopixel_max_value =const(70)    #max value instead of brightness to spare some mem
+print_data = True        # Print data on USB UART / REPL output ?
+send_json_data = True    # Send data as JSON on second UART ?
+backup_data = True       # Write data as CSV files on onboard SPI Flash ?
+data_to_neopixel = True  # Display atmospheric data as color on onboard neopixel ?
+gps_enable = True        # Use GPS module ?
+update_interval = const(10)   # Interval between data acquisition (in seconds)
+datetime_format = "{:04}/{:02}/{:02}_{:02}:{:02}:{:02}"     # Date/time format
+neopixel_max_value =const(70) #max value instead of brightness to spare some mem
 
 #######################
 
@@ -118,7 +117,7 @@ class Data:
 
     @property
     def json(self):
-        """Serialized data to json-formatted string"""
+        """Serialized data to compact json-formatted string"""
         output = '{'
         first_source = True
         for source in self.data.keys():
@@ -150,15 +149,21 @@ class Data:
          * BLUE => humidity : max= 100%, mini=0%
          * GREEN => pression : mini=960hPa, maxi = 1030hPa (range 70hPa)
         """
-
+        # RED componant calculation from temperature data
+        # 10 is the min temperature, 25 is the range
+        # (10+25=35°C = max temperature)
         red = int((self.data['BME']['temp']-10)*neopixel_max_value/25)
         if red > neopixel_max_value:
             red = neopixel_max_value
         if red < 0:
             red = 0
 
+        # BLUE componant calculation: very simple! By definition relative
+        #  humidity cannot be more than 100 or less than 0, physically
         blue = int(self.data['BME']['hum']*neopixel_max_value/100)
 
+        # GREEN component calculation : 960 is the minimum pressure and 70 is
+        #  the range (960+70 = 1030hPa = max pressure)
         green = int((self.data['BME']['press']-960)*neopixel_max_value/70)
         if green > neopixel_max_value:
             green = neopixel_max_value
@@ -181,6 +186,7 @@ class Data:
         except OSError as e:
             print("Err {}: readonly".format(e))
             backup_data = False      #to avoid trying again till next reset
+            # Turn onboard led on to indicate read-only error
             led13.value = True
 
 #############
@@ -253,15 +259,17 @@ bme280 = Adafruit_BME280_I2C(i2c, address=0x76)
 # Battery voltage
 vbat = AnalogIn(microcontroller.pin.PA07)
 
+#Set the pin to control the power to GPS module
 gps_en_pin = DigitalInOut(microcontroller.pin.PB02)
 gps_en_pin.direction = Direction.OUTPUT
 
+#Set the pin N°13 to use the onboard LED as read-only/read-write indicator
 led13 = DigitalInOut(microcontroller.pin.PA17)
 led13.direction = Direction.OUTPUT
 led13.value = False
 
-# GPS on FeatherWing board
-gps_en_pin.value = not gps_enable
+# Set GPS module on FeatherWing board
+gps_en_pin.value = not gps_enable  #Set enable pin high to disable GPS module
 if gps_enable:
     gps_uart = UART(microcontroller.pin.PA10, microcontroller.pin.PA11,
                     baudrate=9600, timeout=3000)
@@ -270,12 +278,13 @@ if gps_enable:
     gps.send_command('PMTK314,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0')
     gps.send_command('PMTK220,1000')    # 1000 ms refresh rate
 
-# second UART to communicate with raspberry pi GPIO
+# Second UART to communicate with raspberry pi (throught GPIO)
 if send_json_data:
     rpi_uart = UART(microcontroller.pin.PB10, microcontroller.pin.PB11,
                     baudrate=115200, timeout=2000)
 
-# Integrated Neopixel
+# Set onboard Neopixel : used as atmo data output
+#  brightness is fixed to 1 to spare some memory. Use neopixel_max_value instead
 if data_to_neopixel:
     pixel = neopixel.NeoPixel(microcontroller.pin.PA06, 1, brightness=1)
 else:
@@ -284,15 +293,18 @@ else:
     pixel[0] = (0,0,0)
     pixel = None
 
+#Finally check if data directories exist
 check_data_dir()
 
 #############
 # Main loop #
 #############
 
+#Create the Data object
 data = Data()
-last_update = time.monotonic()
 
+#Init timer
+last_update = time.monotonic()
 while True:
 
     if gps_enable: