Pulse Meter

  # apt install python3-paho-mqtt python3-gpiozero
  # https://forum.micropython.org/viewtopic.php?t=7224
  # https://github.com/sjmelia/pi-electricity-monitor/blob/master/monitor.py
  # https://www.vishay.com/resistors/pulse-energy-calculator/
  # https://learn.openenergymonitor.org/electricity-monitoring/pulse-counting/introduction-to-pulse-counting

  from paho.mqtt import client as mqtt_client

  from gpiozero import LED, DigitalInputDevice
  from signal import pause

  import random, time, os, logging, json, systemd.daemon

  MQTT_TOPIC = "test/test"
  MQTT_BROKER = "mqtt.local"
  MQTT_PORT = 1883
  MQTT_CLIENT_ID = f'python-mqtt-{random.randint(0, 1000)}'
  MQTT_USER = "test"
  MQTT_PASSWORD = "test"

  # Mandatory, which PIN is the photodiode connected to?
  PD_PIN = 23

  # This was used when writing this script, set to true and connect a
  # LED to the correct pin
  BLINK_LED = os.environ.get("BLINK_LED", False)
  LED_PIN = 24 # Optional


  class PulseMeter(object):
      def __init__(self, mqtt_topic=MQTT_TOPIC, pulse_rate=1000):
          self.last_pulse = False
          self.pulse_start_time = False
          self.delta = 0
          self.current_power = 0.0
          self.pulse_rate = pulse_rate
          self.mqtt_topic = mqtt_topic
          self.mqtt_client = self.connect_mqtt()
          self.mqtt_client.loop_start()

      def connect_mqtt(self):
          def on_connect(client, userdata, flags, rc):
              logging.debug(f"broker: {MQTT_BROKER}, port: {MQTT_PORT}, client id: {MQTT_CLIENT_ID}")
              if rc == 0:
                  logging.info("Connected to MQTT Broker!")
              else:
                  logging.warn("Failed to connect, return code %d\n", rc)

          client = mqtt_client.Client(MQTT_CLIENT_ID)
          client.username_pw_set(MQTT_USER, MQTT_PASSWORD)
          client.on_connect = on_connect
          client.connect(MQTT_BROKER, MQTT_PORT)
          return client

      def pulse_start(self):
          # This isn't even used, but this looks cooler than just having
          # a pass call here. :)
          self.pulse_start_time = time.time()

      def pulse_end(self):
          # No last time? Probably in startup, ignore and wait for the
          # next pulse...
          if not self.last_pulse:
              self.last_pulse = time.time()
              return

          current_time = time.time()

          self.delta = current_time - self.last_pulse
          self.current_power = 3600 / ( self.delta * self.pulse_rate )
          self.last_pulse = current_time
          logging.debug(f"power: {self.current_power:.3f} kWh delta: {self.delta}")

          self.publish_current_power()

      def publish_current_power(self, precision=3):
          # JSON due to reasons
          output = dict([("power", round(self.current_power, precision))])
          logging.debug(f"Trying to publish: {output}")
          result = self.mqtt_client.publish(self.mqtt_topic, json.dumps(output))

          status = result[0]
          if status != 0:
              logging.warn(f"Failed to send message to topic {self.mqtt_topic}")


  def run():
      logging.basicConfig(level=os.environ.get("LOGLEVEL", "INFO"))
      pm = PulseMeter()
      led = LED(LED_PIN)
      pd = DigitalInputDevice(PD_PIN)

      pd.when_activated = pm.pulse_start
      pd.when_deactivated = pm.pulse_end

      if BLINK_LED:
          led.blink(on_time=0.01, off_time=1.25)

      systemd.daemon.notify('READY=1')
      pause()

  if __name__ == "__main__":
      run()