read_pcf8591.py

#!/usr/bin/env python3
# This file is part of HoneyPi [honey-pi.de] which is released under Creative Commons License Attribution-NonCommercial-ShareAlike 3.0 Unported (CC BY-NC-SA 3.0).
# See file LICENSE or go to http://creativecommons.org/licenses/by-nc-sa/3.0/ for full license details.

# Main Source: http://www.diyblueprints.net/measuring-voltage-with-raspberry-pi/#Measure_Voltage_Python

import smbus
import time
from sensors.sensor_utilities import get_smbus
import logging

logger = logging.getLogger('HoneyPi.read_pcf8591')

# read pin from ts_sensor settings
# AIN0 => Pin 0
# AIN1 => Pin 1
# AIN2 => Pin 2 (default)
# AIN3 => Pin 3

def measure(pin):
    # I2C-addr of YL-40 PCF8591
    i2c_addr = 0x48

    try:
        # Create I2C instance and open the bus
        PCF8591 = smbus.SMBus(get_smbus())

        # set channel to AIN0, AIN1, AIN2 or AIN3
        PCF8591.write_byte(i2c_addr, 0x40+pin)

        # i2cget -y 1 0x48
        data_8bit = PCF8591.read_byte(i2c_addr)
        logger.debug("PCF8591 PIN: AIN" + str(pin) + " measureed raw data: " + str(data_8bit))
        if isinstance(data_8bit, (int, float)):
            return data_8bit
    except IOError as ex:
        if str(ex) == "[Errno 121] Remote I/O error":
            logger.error("Reading PCF8591 failed: Most likely I2C Bus needs a reboot.")
    except Exception as ex:
        logger.exception("Unhaldled exception measure")
    return None

# used by check_wittypi_voltage and initial voltage check
def get_raw_voltage(ts_sensor):
    try:
        if 'pin' in ts_sensor and ts_sensor['pin'] is not None:
            pin = int(ts_sensor['pin'])
        else:
            pin = 2
            logger.debug("get_raw_voltage - No pin defined, using default")

        #factor = 0.09765625 # 25V/256 (=5V analog output signal)
        factor = 16.5/256 # 16.5V/256 | 16.5V max voltage for 0xff (=3.3V analog output signal)
        if 'I2CVoltage' in ts_sensor and ts_sensor['I2CVoltage'] is not None:
            # convert 8 bit number to voltage
            factor = float(ts_sensor['I2CVoltage']) / 256

        Voltage_8bit = measure(pin)
        if Voltage_8bit is not None:
            voltage = Voltage_8bit*factor # convert 8 bit number to voltage
            logger.debug("PCF8591 PIN: AIN" + str(pin) + " voltage: " + str(voltage))
            if isinstance(voltage, (int, float)):
                voltage = round(voltage, 4)
                return voltage

    except Exception as ex:
        logger.exception("Unhaldled exception in get_raw_voltage")

    return None

# used for regular measurement
def measure_pcf8591(ts_sensor):
    fields = {}
    try:
        voltage = get_raw_voltage(ts_sensor)
        if voltage is not None:
            if 'ts_field' in ts_sensor and isinstance(voltage, (int, float)):
                fields[ts_sensor["ts_field"]] = round(voltage, 4)

    except Exception as ex:
        logger.exception("Unhaldled exception in measure_pcf8591")

    return fields