read_chem.py

#!/usr/bin/python

import io         # used to create file streams
import fcntl      # used to access I2C parameters like addresses

import time       # used for sleep delay and timestamps
import string     # helps parse strings
import os
import json
import datetime

i2cid = {}

i2cid["ph"]    = 99
i2cid["orp"]   = 98

class AtlasI2C:
	long_timeout = 1.5         	# the timeout needed to query readings and calibrations
	short_timeout = .5         	# timeout for regular commands
	default_bus = 1         	# the default bus for I2C on the newer Raspberry Pis, certain older boards use bus 0
	default_address = 98     	# the default address for the sensor
	current_addr = default_address

	def __init__(self, address=default_address, bus=default_bus):
		# open two file streams, one for reading and one for writing
		# the specific I2C channel is selected with bus
		# it is usually 1, except for older revisions where its 0
		# wb and rb indicate binary read and write
		self.file_read = io.open("/dev/i2c-"+str(bus), "rb", buffering=0)
		self.file_write = io.open("/dev/i2c-"+str(bus), "wb", buffering=0)

		# initializes I2C to either a user specified or default address
		self.set_i2c_address(address)

	def set_i2c_address(self, addr):
		# set the I2C communications to the slave specified by the address
		# The commands for I2C dev using the ioctl functions are specified in
		# the i2c-dev.h file from i2c-tools
		I2C_SLAVE = 0x703
		fcntl.ioctl(self.file_read, I2C_SLAVE, addr)
		fcntl.ioctl(self.file_write, I2C_SLAVE, addr)
		self.current_addr = addr

	def write(self, cmd):
		# appends the null character and sends the string over I2C
		cmd += "\00"
		cmd = cmd.encode()
		self.file_write.write(cmd)

	def read(self, num_of_bytes=31):
		# reads a specified number of bytes from I2C, then parses and displays the result
		res = self.file_read.read(num_of_bytes)         # read from the board
		response = list(filter(lambda x: x != '\x00', res))     # remove the null characters to get the response
		if response[0] == 1:             # if the response isn't an error
			# change MSB to 0 for all received characters except the first and get a list of characters
			char_list = map(lambda x: chr(x & ~0x80), list(response[1:]))
			# NOTE: having to change the MSB to 0 is a glitch in the raspberry pi, and you shouldn't have to do this!
			return "Command succeeded " + ''.join(char_list)     # convert the char list to a string and returns it
		else:
			return "Error " + str(response[0])

	def query(self, string):
		# write a command to the board, wait the correct timeout, and read the response
		self.write(string)

		# the read and calibration commands require a longer timeout
		if((string.upper().startswith("R")) or
			(string.upper().startswith("CAL"))):
			time.sleep(self.long_timeout)
		elif string.upper().startswith("SLEEP"):
			return "sleep mode"
		else:
			time.sleep(self.short_timeout)

		return self.read()

	def close(self):
		self.file_read.close()
		self.file_write.close()

	def list_i2c_devices(self):
		prev_addr = self.current_addr # save the current address so we can restore it after
		i2c_devices = []
		for i in range (0,128):
			try:
				self.set_i2c_address(i)
				self.read()
				i2c_devices.append(i)
			except IOError:
				pass
		self.set_i2c_address(prev_addr) # restore the address we were using
		return i2c_devices

def main():
  device = AtlasI2C()

  while(1):
    data = {}
    data['sensor'] = []

    for tmpi2c in i2cid:
      tsnow = datetime.datetime.now()
      device.set_i2c_address(i2cid[tmpi2c])
      result = device.query("R")
      print ("%s - %s" % (tmpi2c, result))
      value = float(result.rstrip('\x00').split(' ')[2])
      print ("\n")

      data['sensor'].append({
        'name': tmpi2c,
        'value': value,
        'ts': str(tsnow.year) + '-' + str(tsnow.month) + '-' + str(tsnow.day) + ' ' + str(tsnow.hour) + ':' + str(tsnow.minute) + ':' + str(tsnow.second)
      })

    with open('/home/pi/chem.json', 'w') as outfile:
      json.dump(data, outfile)

    time.sleep(13)



if __name__ == '__main__':
	main()