WindDirection.py

import logging

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

'''
How it works

We uses the weather Meter (https://www.sparkfun.com/products/8942) to collect
wind speed and direction data.
For wind direction, it's basicly a variable resistor. we connect it to pull-up
and check the voltage of it by Versatile Input Phidget 
(https://www.phidgets.com/?tier=3&catid=49&pcid=42&prodid=961) to detect 
direction of the wind.

Wiring Guide:

See https://cdn.sparkfun.com/assets/8/4/c/d/6/Weather_Sensor_Assembly_Updated.pdf
for the Wind Vane section.

Voltage is supposed to be checked between terminal 2 and 5 in the RJ45 scoket

Please Note:

1. The voltage-direction table from above link are idea case values, it varies
from different pull-up voltages and even different temperatures.
To tolerant these variations, we take the voltages as mid point value, and
and extend the valid range to the middle of next mid point, that's what the
init_voltage_range_map method in this class doing.

2. The direction we get is relative to the boat's heading direction, we need to 
compensat it with current boat's heading direction to get the true wind 
direction

'''


class WindDirectionDevice(Device):
    def __init__(self, HUB_SERIAL_NUM, PORT_NUM):

        # voltage to direction mapping when connect to a 10k 5v pull up
        self.v_d_tuples_raw = [
            (3.84, 0.0),
            (1.98, 22.5),
            (2.25, 45.0),
            (0.41, 67.5),
            (0.45, 90.0),
            (0.32, 112.5),
            (0.90, 135.0),
            (0.62, 157.5),
            (1.40, 180.0),
            (1.19, 202.5),
            (3.08, 225.0),
            (2.93, 247.5),
            (4.62, 270.0),
            (4.04, 292.5),
            (4.33, 315.0),
            (3.43, 337.5),
        ]
        self.v_d_tuples = []
        self.init_voltage_range_map()

        self.ch = VoltageInput()
        self.ch.setDeviceSerialNumber(HUB_SERIAL_NUM)
        self.ch.setHubPort(PORT_NUM)

        super(WindDirectionDevice, self).__init__(self.ch)

    def on_attach(self):
        self.ch.setDataInterval(500)
        self.ch.setVoltageChangeTrigger(0.01)
        self.listen("VoltageChange", self.onVoltageChangeHandler)

    def onVoltageChangeHandler(self, ch, voltage):
        logging.debug("voltage changed to %f", voltage)
        self.set_event_val("wind_direction", self.find_direction(voltage))

    def init_voltage_range_map(self):
        self.v_d_tuples_raw = sorted(
            self.v_d_tuples_raw, key=lambda v_d_map: v_d_map[0])

        previous_range_end = 0.0
        for idx, v_d_tuple in enumerate(self.v_d_tuples_raw):
            mid_point = v_d_tuple[0]
            direction = v_d_tuple[1]
            if (idx + 1) == len(self.v_d_tuples_raw):
                next_midpoint = self.v_d_tuples_raw[idx - 1][0]
            else:
                next_midpoint = self.v_d_tuples_raw[idx + 1][0]
            margin = abs((next_midpoint - mid_point)/2)
            range_start = previous_range_end
            range_end = mid_point + margin
            previous_range_end = range_end
            v_range = (range_start, range_end)
            self.v_d_tuples.append((v_range, direction))

    def find_direction(self, voltage):
        for v_range, direction in self.v_d_tuples:
            if v_range[0] < voltage <= v_range[1]:
                return direction
        return None