01_basics.py

###
 # Copyright 2017, Google, Inc.
 # Licensed under the Apache License, Version 2.0 (the `License`);
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
 # 
 #    http://www.apache.org/licenses/LICENSE-2.0
 # 
 # Unless required by applicable law or agreed to in writing, software
 # distributed under the License is distributed on an `AS IS` BASIS,
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
### 

#!/usr/bin/python

from sense_hat import SenseHat
import datetime
import time
import jwt
import paho.mqtt.client as mqtt


# Define some project-based variables to be used below. This should be the only
# block of variables that you need to edit in order to run this script

ssl_private_key_filepath = '<ssl-private-key-filepath>'
ssl_algorithm = '<algorithm>' # Either RS256 or ES256
root_cert_filepath = '<root-certificate-filepath>'
project_id = '<GCP project id>'
gcp_location = '<GCP location>'
registry_id = '<IoT Core registry id>'
device_id = '<IoT Core device id>'

# end of user-variables

cur_time = datetime.datetime.utcnow()

def create_jwt():
  token = {
      'iat': cur_time,
      'exp': cur_time + datetime.timedelta(minutes=60),
      'aud': project_id
  }

  with open(ssl_private_key_filepath, 'r') as f:
    private_key = f.read()

  return jwt.encode(token, private_key, ssl_algorithm)

_CLIENT_ID = 'projects/{}/locations/{}/registries/{}/devices/{}'.format(project_id, gcp_location, registry_id, device_id)
_MQTT_TOPIC = '/devices/{}/events'.format(device_id)

client = mqtt.Client(client_id=_CLIENT_ID)
# authorization is handled purely with JWT, no user/pass, so username can be whatever
client.username_pw_set(
    username='unused',
    password=create_jwt())

def error_str(rc):
    return '{}: {}'.format(rc, mqtt.error_string(rc))

def on_connect(unusued_client, unused_userdata, unused_flags, rc):
    print('on_connect', error_str(rc))

def on_publish(unused_client, unused_userdata, unused_mid):
    print('on_publish')

client.on_connect = on_connect
client.on_publish = on_publish

client.tls_set(ca_certs=root_cert_filepath) # Replace this with 3rd party cert if that was used when creating registry
client.connect('mqtt.googleapis.com', 8883)
client.loop_start()

# Could set this granularity to whatever we want based on device, monitoring needs, etc
temperature = 0
humidity = 0
pressure = 0

sense = SenseHat()

for i in range(1, 11):
  cur_temp = sense.get_temperature()
  cur_pressure = sense.get_pressure()
  cur_humidity = sense.get_humidity()

  if cur_temp == temperature and cur_humidity == humidity and cur_pressure == pressure:
    time.sleep(1)
    continue

  temperature = cur_temp
  pressure = cur_pressure
  humidity = cur_humidity

  payload = '{{ "ts": {}, "temperature": {}, "pressure": {}, "humidity": {} }}'.format(int(time.time()), temperature, pressure, humidity)

  # Uncomment following line when ready to publish
#  client.publish(_MQTT_TOPIC, payload, qos=1)

  print("{}\n".format(payload))

  time.sleep(1)

client.loop_stop()