sensor_light.py

#!/usr/bin/python3

"""
Handle an I2C light sensor
"""

# -------------------------------------------------------------
# Based off of bh1750.py from http://www.raspberrypi-spy.co.uk/
# -------------------------------------------------------------
from datetime import datetime
import smbus
from genericsensor import Sensor


class LightSensor(Sensor):
    '''Collect light intensity sensor value and output it to a json file for transfer to server.'''
    DEVICE = 0x23  # Default device I2C address
    # 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
    RPI_SMBUS = 1  # Rev 1 Pi uses 0, Rev 2 Pi uses 1
    VALUE_NAME = 'lux'
    JSON_PREFIX = 'bio_light'
    MEASUREMENT_FMT = '{:7.1f}'

    def __init__(self):
        super().__init__()
        self.bus = smbus.SMBus(LightSensor.RPI_SMBUS)

    def get_value(self):
        data = self.bus.read_i2c_block_data(LightSensor.DEVICE,
                                            LightSensor.ONE_TIME_HIGH_RES_MODE_2)
        return ((data[0] << 8) | data[1]) / 1.2

    def _monitor_value(self, callback):
        raise NotImplementedError('Light sensor does not support monitoring.')


def main():
    '''Code to run when module is executed standalone'''
    sensor = LightSensor()
    value = sensor.get_value()
    print(value)
    sensor.generate_file(
        LightSensor.VALUE_NAME,
        LightSensor.MEASUREMENT_FMT.format(value),
        LightSensor.JSON_PREFIX,
        datetime.utcnow())


if __name__ == '__main__':
    main()