TDM Edge Dispatcher

In TDM Edge Gateway Reference Architecture the Edge Gateway can have sensors directly attached to its connectors. Depending on the type of interface or bus to which they are connected, a different micro-service takes care of establishing the connection, configuring the sensors on that interface and polling them periodically. For the sensor used in this reference design, the HTU21D temperature and humidity sensor, the handler is called Edge Device Handler (HTU21D Publisher is the legacy name and will be changed in the future).

This handler opens the interface on the I2C bus on which the sensor operates and, at time interval set in the configuration file or command line, pools the sensor and sends to the local MQTT broker the message with the parameters detected, in this case temperature, humidity and the dew point calculated from the first two.

Other data sent are internal housekeeping data like, kernel version, memory in use, current cpu load and others. See 'Data collected' section below.

Configurations

Settings are retrieved from both configuration file and command line. Values are applied in the following order, the last overwriting the previous:

1. configuration file section 'GENERAL' for the common options (logging, local MQTT broker...);
2. configuration file section 'HTU21D_publisher' for both common and specific options;
3. command line options.

Configuration file

The options mqtt_host and mqtt_port now are deprecated and no longer recognized. mqtt_local_host and mqtt_local_port must be used instead.

• mqtt_local_host

  hostname or address of the local broker (default: localhost)

• mqtt_local_port

  port of the local broker (default: 1883)

• logging_level

  threshold level for log messages (default: 20)

• influxdb_host

  hostname or address of the influx database (default: localhost)

• influxdb_port

  port of the influx database (default: 8086)

• gps_location

  GPS coordinates of the sensor as latitude,longitude (default: 0.0,0.0)

• htu_interval

  interval in seconds for HTU21D sensor data acquisition and publication (default: 60 secs)

• hkp_interval

  interval in seconds for Housekeeping data acquisition and publication (default: 60 secs)

• i2c_bus

  I2C bus number to which the sensor is attached (default: 1)

When a settings is present both in the GENERAL and application specific section, the application specific is applied to the specific handler.

Options accepted in GENERAL section

• mqtt_local_host
• mqtt_local_port
• influxdb_host
• influxdb_port
• logging_level
• gps_location

In this example, the logging_level settings is overwritten to 1 only for this handler, while other handlers use 0 from the section GENERAL:

[GENERAL]
mqtt_local_host = mosquitto
mqtt_local_port = 1883
influxdb_host = influxdb
influxdb_port = 8086
gps_location=0.0,0.0
logging_level = 0

[HTU21D_publisher]
htu_interval=60
hkp_interval=3600
logging_level = 1
i2c_bus = 1

Command line

• -h, --help

  show this help message and exit

• -c FILE, --config-file FILE

  specify the config file

• -l LOGGING_LEVEL, --logging-level LOGGING_LEVEL

  threshold level for log messages (default: 20)

• --mqtt-host MQTT_HOST

  hostname or address of the local broker (default: localhost)

• --mqtt-port MQTT_PORT

  port of the local broker (default: 1883)

• --i2c-bus I2C_BUS

  I2C bus number to which the sensor is attached (default: 1)

• --htu-interval INTERVAL

  interval in seconds for HTU21D sensor data acquisition and publication (default: 60 secs)

• --hkp-interval INTERVAL

  interval in seconds for Housekeeping data acquisition and publication (default: 60 secs)

• --influxdb-host INFLUXDB_HOST

  hostname or address of the influx database (default: localhost)

• --influxdb-port INFLUXDB_PORT

  port of the influx database (default: 8086)

• --gps-location GPS_LOCATION

  GPS coordinates of the sensor as latitude,longitude (default: 0.0,0.0)

Data Collected

Data collected by the Edge Device Handler are sent with two MQTT messages to the TDM Cloud:

HTU21 Message

• dateObserved measurement date in ISO format;
• timestamp measurement date as Unix Epoch;
• latitude from configuration file/command line;
• longitude from configuration file/command line;
• temperature from HTU21D sensor (also stored in the internal Influx DB);
• humidity from HTU21D sensor (also stored in the internal Influx DB);
• dewpoint computed from data HTU21D sensor (also stored in the internal Influx DB).

HOUSEKEEPING Message

• dateObserved measurement date in ISO format;
• timestamp measurement date as Unix Epoch;
• latitude from configuration file/command line;
• longitude from configuration file/command line;
• lastBoot date of the last boot;
• operatingSystem Operating System (Linux);
• kernelRelease release of the kernel;
• kernelVersion build of the current kernel;
• systemArchitecture CPU architecture;
• cpuCount total CPU number;
• diskTotal total DISK (SD) space in MB;
• diskFree free DISK (SD) space available in MB;
• memoryTotal total RAM memory in MB;
• memoryFree free RAM memory available in MB
• swapTotal total Swap space in MB;
• swapFree free Swap memory available in MB.