Continual Pressure/Temperature Monitoring (run on a cronjob)

bmp.py

# I didn't write this code. I just found it online.

# make sure to install python-smbus using below command
# sudo apt-get install python-smbus
import smbus
import time
from ctypes import c_short

DEVICE = 0x77 # Default device I2C address

#bus = smbus.SMBus(0)  # Rev 1 Pi uses 0
bus = smbus.SMBus(1) # Rev 2 Pi uses 1

def convertToString(data):
  # Simple function to convert binary data into
  # a string
  return str((data[1] + (256 * data[0])) / 1.2)

def getShort(data, index):
  # return two bytes from data as a signed 16-bit value
  return c_short((data[index] << 8) + data[index + 1]).value

def getUshort(data, index):
  # return two bytes from data as an unsigned 16-bit value
  return (data[index] << 8) + data[index + 1]

def readBmp180Id(addr=DEVICE):
  # Chip ID Register Address
  REG_ID     = 0xD0
  (chip_id, chip_version) = bus.read_i2c_block_data(addr, REG_ID, 2)
  return (chip_id, chip_version)

def readBmp180(addr=0x77):
  # Register Addresses
  REG_CALIB  = 0xAA
  REG_MEAS   = 0xF4
  REG_MSB    = 0xF6
  REG_LSB    = 0xF7
  # Control Register Address
  CRV_TEMP   = 0x2E
  CRV_PRES   = 0x34
  # Oversample setting
  OVERSAMPLE = 3    # 0 - 3

  # Read calibration data
  # Read calibration data from EEPROM
  cal = bus.read_i2c_block_data(addr, REG_CALIB, 22)

  # Convert byte data to word values
  AC1 = getShort(cal, 0)
  AC2 = getShort(cal, 2)
  AC3 = getShort(cal, 4)
  AC4 = getUshort(cal, 6)
  AC5 = getUshort(cal, 8)
  AC6 = getUshort(cal, 10)
  B1  = getShort(cal, 12)
  B2  = getShort(cal, 14)
  MB  = getShort(cal, 16)
  MC  = getShort(cal, 18)
  MD  = getShort(cal, 20)

  # Read temperature
  bus.write_byte_data(addr, REG_MEAS, CRV_TEMP)
  time.sleep(0.005)
  (msb, lsb) = bus.read_i2c_block_data(addr, REG_MSB, 2)
  UT = (msb << 8) + lsb

  # Read pressure
  bus.write_byte_data(addr, REG_MEAS, CRV_PRES + (OVERSAMPLE << 6))
  time.sleep(0.04)
  (msb, lsb, xsb) = bus.read_i2c_block_data(addr, REG_MSB, 3)
  UP = ((msb << 16) + (lsb << 8) + xsb) >> (8 - OVERSAMPLE)

  # Refine temperature
  X1 = ((UT - AC6) * AC5) >> 15
  X2 = (MC << 11) / (X1 + MD)
  B5 = X1 + X2
  temperature = int(B5 + 8) >> 4
  temperature = temperature / 10.0

  # Refine pressure
  B6  = B5 - 4000
  B62 = int(B6 * B6) >> 12
  X1  = (B2 * B62) >> 11
  X2  = int(AC2 * B6) >> 11
  X3  = X1 + X2
  B3  = (((AC1 * 4 + X3) << OVERSAMPLE) + 2) >> 2

  X1 = int(AC3 * B6) >> 13
  X2 = (B1 * B62) >> 16
  X3 = ((X1 + X2) + 2) >> 2
  B4 = (AC4 * (X3 + 32768)) >> 15
  B7 = (UP - B3) * (50000 >> OVERSAMPLE)

  P = (B7 * 2) / B4

  X1 = (int(P) >> 8) * (int(P) >> 8)
  X1 = (X1 * 3038) >> 16
  X2 = int(-7357 * P) >> 16
  pressure = int(P + ((X1 + X2 + 3791) >> 4))
  #pressure = float(pressure / 100.0)


  altitude = 44330.0 * (1.0 - pow(pressure / 101325.0, (1.0/5.255)))
  altitude = round(altitude,2)

  return (temperature,pressure,altitude)

take-reading.py

#! /usr/bin/env python3
import bmp
import os.path
import sqlite3
import time

# This script runs and collects a single reading, writes it to a db, then exits
db_path = os.path.expanduser('~/data/temp-and-pressure/readings.db')

"""
CREATE TABLE readings(
    id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
    temperature NUMERIC,
    pressure NUMERIC,
    altitude NUMERIC,
    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
);
"""


def main():
    temp, pressure, altitude = bmp.readBmp180()


    connection = sqlite3.connect(db_path)
    cursor = connection.cursor()
    print(f'inserting into main.readings (t: {temp}, p: {pressure}, a: {altitude})')
    cursor.execute(
        'insert into main.readings (temperature, pressure, altitude) values (?, ?, ?)',
        (temp, pressure, altitude),
    )
    connection.commit()
    connection.close()


if __name__ == '__main__':
    main()