weathervane.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# vim: set expandtab tabstop=4 shiftwidth=4 :

# weathervane.py - A module that that gets readings from a standard multiple
#   switches-and-resisters weather vane (wind vane) connected to GPIO pin 6
#   (RasPi header pin 31).  After 
# https://projects.raspberrypi.org/en/projects/build-your-own-weather-station/7

# By: The Doctor <drwho at virtadpt dot net>

# License: GPLv3

# v1.1 - Reworked the weather vane signal interpretation code because my unit
#        isn't stable.  I still hate hardcoding magick numbers but this way
#        actually makes the 'vane usable.
# v1.0 - Initial release.

# TO-DO:
# - Make the channel of the ADC chip configurable.
# - Use real logger code rather than a bunch of print()s.
# - The table of values-to-directions should probably be configurable, but I'm
#   not sure yet how to do that.
# - Add a utility that helps a user calculate their own table of direction/
#   values?

# Load modules.
import gpiozero
import logging
import sys
import time

import globals

# Constants.
# Channel (pin) of the ADC the weather vane is connected to.
channel = 0

# Value of the reference voltage the ADC is receiving on pin 15.  The circuit
# I'm using (and hardwired) draws power from pin 1 on the RasPi (3.3 VDC).
reference_voltage = 3.3

# Global variables.

# I originally used this research code to generate the values for my weather
# vane (and you should, too, just to be safe), but I found that even then the
# values aren't necessarily stable.  There's a noticeable variation in the
# signal even though it's coming from a static resistor.  So, I hardcoded a
# heuristic (+/- 0.1) in the core code to make it work somewhat more reliably.
# I need to make the values and the heuristics configurable so that more folks
# can use this code without having to hand-hack my code.
#
# import gpiozero
# import time
# adc = gpiozero.MCP3008(channel=0)
# values = []
# while True:
#   wind = round(adc.value * 3.3, 1)
#   if not wind in values:
#       values.append(wind)
#       print("Got new value: %s" % wind)
#       print()
#   time.sleep(5)
#

# Core code...
# get_direction(): The function that does everything by calling everything
#   else.  Here so that it can be called from Weather Station Bot's central
#   module, as well as __main__ for testing.  Returns a hash table containing
#   the sample data.
def get_direction():

    # Voltage from the weather vane.
    value = 0.0

    # Set up the GPIO object.
    if not globals.weathervane:
        globals.weathervane = gpiozero.MCP3008(channel=channel)

    # Get a sample from the weather vane.
    value = round(globals.weathervane.value * reference_voltage, 1)
    logging.debug("Value from the weather vane: %s" % value)

    # Interpret the value from the weather vane.
    if (value >= 2.0) and (value <= 2.2):
        return("north")
    if (value >= 1.7) and (value <= 1.9):
        return("northeast")
    if (value >= 2.9) and (value <= 3.1):
        return("east")
    if (value >= 2.6) and (value <= 2.8):
        return("southeast")
    if (value >= 2.3) and (value <= 2.5):
        return("south")
    if (value >= 1.2) and (value <= 1.4):
        return("southwest")
    if (value >= 0.1) and (value <= 0.3):
        return("west")
    if (value >= 0.9) and (value <= 1.1):
        return("northwest")

    # No match.
    return None

# Exercise my code.
if __name__ == "__main__":
    # Configure the logger.  DEBUG for interactive testing.
    logging.basicConfig(level=10, format="%(levelname)s: %(message)s")
    logger = logging.getLogger(__name__)

    print("Starting test run.")

    sensor = gpiozero.MCP3008(channel=channel)
    for i in range(10):
        temp = None
        temp = get_direction()
        if temp:
            print("The weather vane is pointing %s." % temp)
        else:
            print("The weather vane returned a spurious value.  I saw: %s" % temp)
        time.sleep(5)

    print("End of test run.")
    sys.exit(0)

# Fin.