BeagleBone LCD Thermometer

thermometer.py

#!/usr/bin/python
"""
This script assumes that you have a LCD connected to a RaspberryPi or BeagleBone
Black as as described in this tutorial:
  https://learn.adafruit.com/character-lcd-with-raspberry-pi-or-beaglebone-black
along with a temperature sensor as described in this tutorial:
  https://learn.adafruit.com/measuring-temperature-with-a-beaglebone-black
"""

from collections import deque
import datetime
import sys
import time

import Adafruit_BBIO.ADC as ADC
import Adafruit_CharLCD as LCD

# Raspberry Pi pin configuration:
# lcd_rs        = 27  # Note this might need to be changed to 21 for older revision Pi's.
# lcd_en        = 22
# lcd_d4        = 25
# lcd_d5        = 24
# lcd_d6        = 23
# lcd_d7        = 18
# lcd_backlight = 4

# BeagleBone Black configuration:
lcd_rs        = 'P8_8'
lcd_en        = 'P8_10'
lcd_d4        = 'P8_18'
lcd_d5        = 'P8_16'
lcd_d6        = 'P8_14'
lcd_d7        = 'P8_12'
lcd_backlight = 'P8_7'

# Define LCD column and row size for 16x2 LCD.
lcd_columns = 16
lcd_rows    = 2

# Initialize the LCD using the pins above.
lcd = LCD.Adafruit_CharLCD(
    lcd_rs, lcd_en, lcd_d4, lcd_d5, lcd_d6, lcd_d7,
    lcd_columns, lcd_rows, lcd_backlight)

# Initialze the temp sensor
sensor_pin = 'P9_40'
ADC.setup()


class LineScroller(object):
    """ Scroll text across LCD """
    def __init__(self, max_len, pause_len):
        self.pause_len = pause_len
        self.max_len = max_len

        self.offset = 0
        self.pause = 0
        self.forward = True

    def output(self, txt):
        output = txt[self.offset:(self.max_len + self.offset)]
        self._prep_next_position(txt)
        return output

    def _prep_next_position(self, txt):
        # Pass on pause
        if self.pause:
            self.pause -= 1
            return

        # Update offset
        self.offset += 1 if self.forward else -1

        # Reverse direction at string bounds
        if ((self.offset + self.max_len) == len(txt)) or (self.offset == 0):
          self.forward = not self.forward
          self.pause = self.pause_len

def get_datetime_str():
    date_out = datetime.datetime.now().strftime('%B %d, %Y')
    time_out = datetime.datetime.now().strftime('%I:%M%p').lstrip('0')
    return '{time}, {date}'.format(
        date=date_out,
        time=time_out,
    )

def get_temp_str(buf=None):
    """
    Get temperature readings from sensor. Optionaly, pass in a deque buffer
    with a fixed length to base measurements on average of past N readings.
    """
    buf = buf if buf is not None else []
    reading = ADC.read(sensor_pin)
    buf.append(reading * 1800)  # 1.8V reference = 1800 mV
    millivolts = sum(buf)/len(buf)
    temp_c = (millivolts - 500) / 10
    temp_f = (temp_c * 9/5) + 32
    temp_out = 'C={c}{deg} F={f}{deg}'
    return temp_out.format(
        c=round(temp_c, 1),
        f=round(temp_f, 1),
        deg=''
    ).ljust(lcd_columns)


line_one = LineScroller(max_len=lcd_columns, pause_len=5)
temp_buf = deque(maxlen=5)
while True:
    try:
        out = []
        out.append(line_one.output(get_datetime_str()))
        out.append(get_temp_str(temp_buf))

        # Print a two line message
        output = '\n'.join(out)
        lcd.set_cursor(0,0)
        lcd.message(output)
        time.sleep(0.5)
    except KeyboardInterrupt:
        sys.stdout.write('\nExiting.\n')
        exit()