Add module for BH1750 light level sensor (#72)

.gitignore

@@ -95,3 +95,7 @@ ENV/
 
 #Kate
 *.kate-swp
+
+# User's Config File
+config.yml
+

README.md

@@ -18,6 +18,7 @@ Sensors
 
 - LM75 i2c temperature sensor (`lm75`)
 - DHT11 DHT22 AM2302 temperature/humidity sensor (`dht22`)
+- BH1750 light level sensor (`bh1750`)
 
 Installation
 ------------
@@ -136,6 +137,18 @@ sensor_inputs:
     digits: 4 # number of digits to be round
     type: humidity # Can be temperature or humidity   
 
+sensor_modules:
+  - name: bh1750
+    module: bh1750
+    i2c_bus_num: 1
+    chip_addr: 0x23
+
+sensor_inputs:
+  - name: bh1750_lux
+    module: bh1750
+    interval: 10
+    digits: 2
+    
 ```
 
 #### SSL/TLS

pi_mqtt_gpio/modules/bh1750.py

+"""BH1750 Light Intensity Sensor."""
+from pi_mqtt_gpio.modules import GenericSensor
+
+
+CONFIG_SCHEMA = {
+    "i2c_bus_num": {"type": "integer", "required": True, "empty": False},
+    "chip_addr": {"type": "integer", "required": True, "empty": False},
+}
+
+# Define some constants from the datasheet
+DEVICE = 0x23       # Default device I2C address
+POWER_DOWN = 0x00   # No active state
+POWER_ON = 0x01     # Power on
+RESET = 0x07        # Reset data register value
+# Start measurement at 4lx resolution. Time typically 16ms.
+CONTINUOUS_LOW_RES_MODE = 0x13
+# Start measurement at 1lx resolution. Time typically 120ms
+CONTINUOUS_HIGH_RES_MODE_1 = 0x10
+# Start measurement at 0.5lx resolution. Time typically 120ms
+CONTINUOUS_HIGH_RES_MODE_2 = 0x11
+# Start measurement at 1lx resolution. Time typically 120ms
+# Device is automatically set to Power Down after measurement.
+ONE_TIME_HIGH_RES_MODE_1 = 0x20
+# Start measurement at 0.5lx resolution. Time typically 120ms
+# Device is automatically set to Power Down after measurement.
+ONE_TIME_HIGH_RES_MODE_2 = 0x21
+# Start measurement at 1lx resolution. Time typically 120ms
+# Device is automatically set to Power Down after measurement.
+ONE_TIME_LOW_RES_MODE = 0x23
+
+
+class Sensor(GenericSensor):
+    """Implementation of Sensor class for the BH1750 light sensor."""
+
+    def __init__(self, config):
+        """Initialize sensor class."""
+        import smbus
+
+        self.bus = smbus.SMBus(config["i2c_bus_num"])
+        self.address = config["chip_addr"]
+
+    def setup_sensor(self, config):
+        """Perform setup for the sensor."""
+        return True  # nothing to do here
+
+    def get_value(self, config):
+        """Get the light value from the sensor."""
+        value = self.bus.read_i2c_block_data(self.address,
+                                             ONE_TIME_HIGH_RES_MODE_1)
+        value = (value[1] + (256 * value[0])) / 1.2
+        return value