Added UV sensor code. Calculations may be inaccurate.

backend/sensors.py

@@ -133,14 +133,14 @@ class LxMeter:
             temp = self.bus.read_byte_data(self.addr, 0xa1)
             self.bus.write_byte_data(self.addr, 0xa1, (temp & 0xfc) | time)
         except:
-            raise Exception('An error occured setting lux integration time')
+            raise Exception('An exception occured setting lux integration time')
 
     def getIntTime(self):
         '''Get the lux sensor integration time.'''
         try:
             return self.bus.read_byte_data(self.addr, 0xa1) & 0x03
         except:
-            raise Exception('An error occured getting lux integration time')
+            raise Exception('An exception occured getting lux integration time')
 
     def getData(self):
         '''return the calculated lux value'''
@@ -148,16 +148,85 @@ class LxMeter:
             chA = self.bus.read_word_data(self.addr, 0xac)
             chB = self.bus.read_word_data(self.addr, 0xae)
         except:
-            raise Exception('An error occured fetching lux channels')
+            raise Exception('An exception occured fetching lux channels')
 
+        # scary computations ahead! refer to the apds-9301 datasheet!
         if chB/chA <= 0.5 and chB/chA > 0:
-            lux = (0.0304*chA) - (0.062*chA*((chB/chA)**1.4))
+            lux = 0.0304*chA - 0.062*chA*(chB/chA)**1.4
         elif chB/chA <= 0.61 and chB/chA > 0.5:
-            lux = (0.0224*chA) - (0.031*chB)
+            lux = 0.0224*chA - 0.031*chB
         elif chB/chA <=0.8 and chB/chA > 0.61:
-            lux = (0.0128*chA) - (0.0153*chB)
+            lux = 0.0128*chA - 0.0153*chB
         elif chB/chA <=1.3 and chB/chA >0.8:
-            lux = (0.00146*chA) - (0.00112*chB)
+            lux = 0.00146*chA - 0.00112*chB
         else:
             lux = 0
         return lux
+
+class UVSensor:
+    def __init__(self, bus=1, addr=0x10):
+        try:
+            self.bus = smbus2.SMBus(bus)
+        except:
+            raise Exception('An exception occured opening SMBus {}'.format(bus))
+
+        try:
+            # enable the sensor and set the integration time
+            self.bus.write_byte_data(addr, 0x00, 0b00010000)
+        except:
+            raise Exception('An exception occured when initalizing the UV Sensor')
+
+    def getABI(self):
+        '''Calculates the UVA and UVB irradiances,
+        along with UV index. Returns [a,b,i]'''
+        
+        try:
+            # read the raw UVA, UVB and compensation values from the sensor
+            aRaw = self.bus.read_word_data(addr, 0x07)
+            bRaw = self.bus.read_word_data(addr, 0x09)
+            c1 = self.bus.read_word_data(addr, 0x0a)
+            c2 = self.bus.read_word_data(addr, 0x0b)
+        except:
+            raise Exception('An exception occured when fetching raw UV data')
+        # scary computations ahead! refer to Vishay app note 84339 and Sparkfun
+        # VEML6075 documentation.
+
+        # first, compensate for visible and IR noise
+        aCorr = aRaw - 2.22 * c1 - 1.33 * c2
+        bCorr = bRaw - 2.95 * c1 - 1.74 * c2
+
+        # second, convert values into irradiances
+        a = aCorr * 0.00110
+        b = bCorr * 0.00125
+
+        # last, calculate the UV index
+        i = (uva + uvb) / 2
+
+        return [a,b,i]
+
+    def getA(self):
+        return self.getABI()[0]
+
+    def getB(self):
+        return self.getABI()[1]
+
+    def getI(self):
+        return self.getABI()[2]
+
+    def on(self):
+        '''Turns the UV sensor on after shutdown.'''
+        try:
+            # write the default value for power on
+            # no configurable params = no bitmask
+            self.bus.write_byte_data(addr, 0x00, 0x10)
+        except:
+            raise Exception('An exception occured when turning the UV sensor on')
+
+    def off(self):
+        '''Shuts the UV sensor down.'''
+        try:
+            # write the default value + the shutdown bit
+            # no configurable params = no bitmask
+            self.bus.write_byte_data(addr, 0x00, 0x11)
+        except:
+            raise Exception('An exception occured when shutting the UV sensor down')