flowmeter.py

import json
import time
import requests
from datetime import datetime
import RPi.GPIO as GPIO


class FlowMeter():
    ''' Class representing the flow meter sensor which handles input pulses
        and calculates current flow rate (L/min) measurement
    '''
    
    def __init__(self):
        self.flow_rate = 0.0
        self.last_time = datetime.now()

    def pulseCallback(self, p):
        ''' Callback that is executed with each pulse received from the sensor '''

        # Calculate the time difference since last pulse recieved
        current_time = datetime.now()
        diff = (current_time - self.last_time).total_seconds()

        # Calculate current flow rate
        hertz = 1. / diff
        self.flow_rate = hertz / 7.5

        # Reset time of last pulse
        self.last_time = current_time

    def getFlowRate(self):
        ''' Return the current flow rate measurment. If a pulse has not been received
            in more than one second, assume that flow has stopped and set flow rate to 0.0
        '''

        if (datetime.now() - self.last_time).total_seconds() > 1:
            self.flow_rate = 0.0

        return self.flow_rate


def main():
    ''' Main function for repeatedly collecting flow rate measurements
        and sending them to the SORACOM API
    '''

    # Configure GPIO pins
    INPUT_PIN = 7
    GPIO.setmode(GPIO.BOARD)
    GPIO.setup(INPUT_PIN, GPIO.IN, pull_up_down=GPIO.PUD_UP)

    # Init FlowMeter instance and pulse callback
    flow_meter = FlowMeter()
    GPIO.add_event_detect(INPUT_PIN,
                          GPIO.RISING,
                          callback=flow_meter.pulseCallback,
                          bouncetime=20)


    # Begin infinite loop
    while True:

        # Get current flow meter reading
        flow_rate = flow_meter.getFlowRate()

        # Build payload
        payload = {
            'datetime': str(datetime.now()),
            'flowr_rate': flow_rate
        }
        
        # Publish to Soracom API
        headers = {'Content-Type': 'application/json'}
        try:
            print('Publishing to SORACOM API...')
            r = requests.post('http://unified.soracom.io',
                              data=json.dumps(payload),
                              headers=headers,
                              timeout=5)
        except:
            print('Error: Connection timeout.')

        # Delay
        time.sleep(5)
        

if __name__ == '__main__':
    main()