WaterSpeed.py

import logging
import math

from Phidget22.Devices.FrequencyCounter import *
from DeviceManager import Device

DIAMETER = 0.0127
SECTIONAL_AREA = math.pi * math.pow(DIAMETER/2, 2)

'''
How it works

We use water flow sensor 
(https://www.robotshop.com/en/seeedstudio-water-flow-sensor.html) to hook to the
Versatile Input Phidget's FrequencyCounter to get speed of flow.
We have 4 of such sensors to measure the water speed in 4 directions: forward, 
backward, left and right.
In order to just measure the direction we desire, we mount a L shape pipe to the
exit end of the seasor, so that when going other directions, no significant 
flow is forced to pass the sensor.

The Math

As documented, f = Q*7.5, Q is the flowspeed in L/min, thus Q = f/7.5 which means
the volume of water pass the meter in one min. devide it by area of the sectional
area to get the speed of water.

'''


class WaterSpeedDevice(Device):
    def __init__(self, water_direction, hub_serial_num, port_num):
        ch = FrequencyCounter()
        ch.setDeviceSerialNumber(hub_serial_num)
        ch.setHubPort(port_num)
        self.event_key_name = "water_speed_" + water_direction
        self.ch = ch

        super(WaterSpeedDevice, self).__init__(ch)

    def get_water_speed(self, frequency):
        # f = Q*7.5, Q is the flowspeed in L/min
        flowspeed = (frequency/7.5) / 60000  # L/min to m3/s
        return flowspeed / SECTIONAL_AREA

    def on_attach(self):
        device = self
        self.ch.setDataInterval(500)

        def on_frequency_change(ch, frequency):
            water_speed = device.get_water_speed(frequency)
            device.set_event_val(device.event_key_name, water_speed)

        self.listen("FrequencyChange", on_frequency_change)