Add concept of additional sensors and add SCD41

enviro/__init__.py

@@ -30,7 +30,13 @@ def get_board():
   if model == "urban":
     import enviro.boards.urban as board
   return board
-
+
+# return any additional sensors connected with Qw/ST
+def get_additional_sensors():
+  if 98 in i2c_devices:
+    import enviro.sensors.scd41 as scd41
+    yield scd41
+
 # set up the activity led
 # ===========================================================================
 from machine import PWM, Timer
@@ -304,9 +310,14 @@ def get_sensor_readings():
   readings = get_board().get_sensor_readings(seconds_since_last)
   readings["voltage"] = 0.0 # battery_voltage #Temporarily removed until issue is fixed
 
+  # Add any additional sensor readings
+  for sensor in get_additional_sensors():
+      for key, value in sensor.get_sensor_readings(seconds_since_last).items():
+          readings[key] = value
+
   # write out the last time log
   with open("last_time.txt", "w") as timefile:
-    timefile.write(now_str)  
+    timefile.write(now_str)
 
   return readings
 

enviro/sensors/scd41.py

@@ -0,0 +1,26 @@
+import time
+
+import breakout_scd41
+
+from enviro import i2c
+
+breakout_scd41.init(i2c)
+breakout_scd41.start()
+
+def get_sensor_readings(seconds_since_last):
+  retries = 25
+  while retries > 0 and not breakout_scd41.ready():
+    time.sleep(0.2)
+    retries -= 1
+
+  if retries == 0:
+    return {}
+
+  scd_co2, scd_temp, scd_humidity = breakout_scd41.measure()
+
+  from ucollections import OrderedDict
+  return OrderedDict({
+    "scd_co2": scd_co2,
+    "scd_temperature": scd_temp,
+    "scd_humidity": scd_humidity
+  })

main.py

@@ -73,9 +73,9 @@
   # here you can customise the sensor readings by adding extra information
   # or removing readings that you don't want, for example:
   # 
-  #   del readings["temperature"]        # remove the temperature reading
+  #   del reading["temperature"]        # remove the temperature reading
   #
-  #   readings["custom"] = my_reading()  # add my custom reading value
+  #   reading["custom"] = my_reading()  # add my custom reading value
 
   # is an upload destination set?
   if enviro.config.destination: