Retrieving pressure and temperature from MPL3115A2 sensor and publishing to Domoticz via MQTT broker

MPL3115A2_domoticz.py

"""
Script interacting with MPL3115A2 sensor via I2C and publishing the resulting
pressure and temperature to a Domoticz server, via MQTT broker.
"""

from smbus import SMBus
import paho.mqtt.publish as publish
import time
import json

ADDR = 0x60
CTRL_REG1 = 0x26
PT_DATA_CFG = 0x13
WHO_AM_I = 0x0C


class MPL3115A2:
    """Interact with MPL3115A2 I2C barometric module"""
    def __init__(self, bus):
        self.bus = SMBus(bus)

    def check_myself(self):
        i = self.read(WHO_AM_I)
        return i == 0xc4

    def readn(self, reg, data):
        time.sleep(0.010)
        attempt = 10
        while attempt > 0:
            try:
                return self.bus.read_i2c_block_data(ADDR, reg, data)
            except IOError:
                time.sleep(0.5)
                attempt -= 1
        raise IOError("Failed 10 times to read")

    def read(self, reg):
        return self.readn(reg, 1)[0]

    def status(self):
        return self.read(0x00)

    def write(self, reg, data):
        self.bus.write_i2c_block_data(ADDR, reg, [data])

    def set_event_flag(self):
        self.write(PT_DATA_CFG, 0x07)

    def toggle_one_shot(self):
        setting = self.read(CTRL_REG1)
        if (setting & 0x02) == 0:
            self.write(CTRL_REG1, (setting | 0x02))

    def wait_for_data(self):
        self.toggle_one_shot()
        status = dev.status()
        while (status & 0x08) == 0:
            status = dev.status()
            time.sleep(0.5)

dev = MPL3115A2(0)

if not dev.check_myself():
    print("Device not active.")
    exit(1)

# Set oversample rate to 128
newSetting = dev.read(CTRL_REG1) | 0x38
dev.write(CTRL_REG1, newSetting)

# Enable event flags
dev.set_event_flag()

# Read sensor data
print("Waiting for data...")
dev.wait_for_data()

print("Reading sensor data...")
p_data = dev.readn(0x01, 3)
t_data = dev.readn(0x04, 2)

p_msb = p_data[0]
p_csb = p_data[1]
p_lsb = p_data[2]
t_msb = t_data[0]
t_lsb = t_data[1]

pressure = (p_msb << 10) | (p_csb << 2) | (p_lsb >> 6)
p_decimal = ((p_lsb & 0x30) >> 4)/4.0
pressure = (pressure+p_decimal)/100.0

celsius = t_msb + (t_lsb >> 4)/16.0
fahrenheit = (celsius * 9)/5 + 32

# Check quickly if temperature and pressure are meaningful
if (pressure < 900) or (pressure > 1050) or (celsius < 5) or (celsius > 45):
    print("Meaningless values...")
    exit(1)

print("Pressure and Temperature at "+time.strftime('%m/%d/%Y %H:%M:%S%z'))
print(str(pressure)+" hPa")
print(str(celsius)+" C")
print(str(fahrenheit)+" F")

print("Send data to Domoticz...")

msgs = [
    {
        'topic':"domoticz/in",
        'payload':
            json.dumps(
                {"idx": 17, "nvalue": 0, "svalue": ("%.2f" % celsius)})},
    {
        'topic':"domoticz/in",
        'payload':
            json.dumps(
                {"idx": 18, "nvalue": 0, "svalue": ("%.2f;0" % pressure)})}
]

publish.multiple(msgs, hostname="ds")

Publish an UV sensor (previously added with dummy hardware):

import paho.mqtt.publish as publish
import json

uv = 3.2

publish.single("domoticz/in", json.dumps({"idx": 33, "nvalue": 0, "svalue": ("%.1f;0" % uv)}), hostname="ds")