pi-lightlevel

#!/usr/bin/env python

import time
import picamera
from PIL import Image
import paho.mqtt.client
import mqtt_config
import json
import io
import fractions

#Test in test/, check http://spacehub.somakeit.org.uk
#for advice choosing a topic for production
TOPIC = "somakeit/space/main_room/lightlevel"
POLL_TIME = 300 #seconds

#Camera settings
AWB_GAINS = (fractions.Fraction(77, 64), fractions.Fraction(471, 256))
SHUTTER_SPEED = long(33164)
ISO = long(1600)

#Connect to a broker
mqtt = paho.mqtt.client.Client(client_id=mqtt_config.client_id, clean_session=True)
#Use real root certificates
mqtt.tls_set(("/etc/ssl/certs/ca-certificates.crt"))
mqtt.username_pw_set(mqtt_config.user_name, mqtt_config.password)
mqtt.loop_start()
while True:
    try:
        mqtt.connect(mqtt_config.server, port=mqtt_config.port)
        break
    except Exception as e:
        print "failed to connecct: " + str(e)
        time.sleep(60)
        print "retrying.."

while True:
    stream = io.BytesIO()
    try:
        camera = picamera.PiCamera()
        camera.resolution = (320, 240)
        camera.framerate = 30

        # Fix everything
        camera.shutter_speed = SHUTTER_SPEED
        camera.exposure_mode = 'off'
        camera.awb_mode = 'off'
        camera.awb_gains = AWB_GAINS
        camera.iso = ISO

        #Capture a shot
        camera.capture(stream, format='jpeg')

        camera.close()
        del(camera)

    except Exception as e:
        print "Failed to camera: " + str(e)
        continue

    #process the image
    image = Image.open(stream)
    bwimage = image.convert('L')
    data = (bwimage.getdata())
    light = 1.0*sum(data)/len(data)
    del(stream)
    del(image)
    del(bwimage)

    timestamp = time.time()
    message = json.dumps({"timestamp": timestamp, "lumens": -1, "level": light})
    mqtt.publish(TOPIC, payload=message, qos=0, retain=True)

    time.sleep(POLL_TIME)