Sensor Control

This section covers the configuration and initialisation of DMPACK for sensor data collection. Basic knowledge of regular expressions and familiarity with the Lua syntax are recommended. The sensor control examples are written for Linux and assume DMPACK to be installed to /opt. The path /opt/bin must be added to the global PATH variable.

Humidity Sensor (RS-232)

DKRF400
Figure 7. Driesen + Kern DKRF400 temperature and humidity sensor

The DKRF400 is a temperature and humidity probe made by Driesen + Kern GmbH. The standard probe DKRF400 can be used at temperatures between –40 … +80 °C, with an accuracy of ±0.3 °C at 25 °C. The probe is suitable for the range of 0 … 100 % relative humidity and has an accuracy of ±1.8 % in the range of 20 … 80 %. The sensor returns the following measured parameters:

  • temperature [°C],

  • relative humidity [%],

  • absolute humidity [g/m3],

  • dew point [°C],

  • wet-bulb temperature [°C].

The DKRF400 is available with analog and digital output signals (RS-232, USB, RS-485). This section is based on the digital version with RS-232 interface. Use an USB serial adapter if the sensor node does not provide a distinct COM port. By default, the digital DKRF400 starts sending values over the serial line once the sensor is connected to the host. We can change from stream to request/response mode through a basic ASCII protocol: the command s\r stops the continuous output of reponses and the command Meter\r returns a single response (\r is carriage return).

Serial interface specifications of the DKRF400 sensor

Name

DKRF400

Vendor

Driesen + Kern GmbH

Interface

RS-232

Protocol

ASCII

Connector

D-sub (DE-9)

Baud rate

9600

Byte size

8

Parity

none

Stop bits

2

DTR

enabled

RTS

enabled

The serial connection can be tested with minicom(1).

$ sudo apt-get install minicom

In this case, the first COM port is mapped to device /dev/ttyS0. The user under which minicom(1) runs must be member of group dialout to access the device. The command-line argument -s is passed to display the setup menu at start:

$ minicom -s

Select Serial port setup to change the TTY parameters to 9600 baud and 8N2. Return and select Exit to receive sensor responses:

Welcome to minicom 2.8

OPTIONS: I18n
Port /dev/ttyS0, 20:56:16

Press CTRL-A Z for help on special keys

-MTAA-DKrF400
Enhanced Architecture HW.V. 4.0
SW.V. 4.12 build Sep 28 2010 13:49:50C 530 166
(c) Driesen+Kern GmbH Bad Bramstedt Germany
SNr: XXXXX
Range:     -40'C   ..       80'C               0%    ..      100%
status: 0840    08      00      00      01      00      80      25      01
Vref: 2500.000000
SHT1X7X
   26.84 'C        53.03 %         13.52 g/m3      16.46 'C        19.97 'C
   26.84 'C        53.03 %         13.52 g/m3      16.46 'C        19.97 'C
   26.84 'C        52.97 %         13.51 g/m3      16.44 'C        19.96 'C

The key combination CTRL + A O shows the options menu again, and CTRL + A X exits minicom(1).

Databases

Use dminit to create the observation and the log database in directory /opt/var/dmpack/:

$ cd /opt/var/dmpack/
$ dminit --database observ.sqlite --type observ --wal
$ dminit --database log.sqlite --type log --wal

Create node node-1, sensor dkrf400, and target target-1 in database /opt/var/dmpack/observ.sqlite through dmdbctl:

$ dmdbctl -d observ.sqlite -C node --id node-1 --name "Node 1"
$ dmdbctl -d observ.sqlite -C sensor --id dkrf400 --name "DKRF400" --node node-1
$ dmdbctl -d observ.sqlite -C target --id target-1 --name "Target 1"

Configuration

regex101.com
Figure 8. Creating the regular expression pattern of the DKRF400 response with regex101.com

On request Meter\r, the sensor returns an ASCII response containing temperature, relative humidity, absolute humidity, dew point, and wet-bulb temperature:

   21.90 'C  \t   57.60 %   \t   11.11 g/m3\t   13.16 'C  \t   16.50 'C  \t\r

The tab character 0x09 and the carriage return 0x0d in the raw response of the sensor will be replaced by dmserial with \t and \r respectively. The program also extracts the values from the raw response and adds them to the entries in the pre-defined responses list if a regular expression pattern has been declared. The following pattern was made with the online tool regex101.com (Figure 8) and matches the sensor responses of the DKRF400:

^\s*(?<temp>[-0-9.]+)\s.C\s+.t\s+(?<humrel>[-0-9.]+)\s%\s+.t\s+(?<humabs>[-0-9.]+)\sg.m3.t\s+(?<dew>[-0-9.]+)\s.C\s+.t\s+(?<wetbulb>[-0-9.]+)

The group names temp, humrel, humabs, dew, and wetbulb within the pattern must match the names given in the responses list. The name length is limited to 32 characters. Optionally, the responses can be given a unit in attribute unit and a response type in attribute type. If no response type is set, RESPONSE_TYPE_REAL64 (double precision number) is assumed by default.

In the configuration file, each backslash character \ has to be escaped with an additional \. Simply replace every occurance of \ with \\:

^\\s*(?<temp>[-0-9.]+)\\s.C\\s+.t\\s+(?<humrel>[-0-9.]+)\\s%\\s+.t\\s+(?<humabs>[-0-9.]+)\\sg.m3.t\\s+(?<dew>[-0-9.]+)\\s.C\\s+.t\\s+(?<wetbulb>[-0-9.]+)

Set the regular expression pattern as value of attribute pattern in request get_values of observation meter. The complete configuration file of dmserial is listed below.

-- dmserial.conf
-- Global variables of identifiers used in the configuration. The values must
-- match the records added to the database.
node_id   = "node-1"
sensor_id = "dkrf400"
target_id = "target-1"

-- Table of observations to be used in jobs list. The attribute `receivers`
-- contains a list of up to 16 processes to forward the observation to in
-- sequential order.
observs = {
  -- List of sensor commands to be send to the DKRF400.
  {
    -- (1) Start the sensor by sending a single carriage return.
    name = "start",             -- Observation name (required).
    target_id = target_id,      -- Target id (required).
    receivers = { },            -- List of receivers (up to 16).
    requests = {                -- List of requests (up to 8).
      {
        name = "start_sensor",  -- Request name (required).
        request = "\\r",        -- Raw request to send to sensor.
        delimiter = "\\n",      -- Response delimiter.
        pattern = "",           -- RegEx pattern of the response.
        delay = 500             -- Delay in msec to wait afterwards.
      }
    }
  },
  {
    -- (2) Stop "Meter Mode". The sensor response will be ignored if no delimiter
    --     is set (as the DKRF400 does not always return a response to the
    --     command).
    name = "stop",              -- Observation name (required).
    target_id = target_id,      -- Target id (required).
    receivers = { },            -- List of receivers (up to 16).
    requests = {                -- List of requests (up to 8).
      {
        name = "stop_meter",    -- Request name (required).
        request = "s\\r",       -- Raw request to send to sensor.
        delimiter = "",         -- Response delimiter.
        pattern = "",           -- RegEx pattern of the response.
        delay = 500             -- Delay in msec to wait afterwards.
      }
    }
  },
  {
    -- (3) Perform single measurement.
    name = "meter",             -- Observation name (required).
    target_id = target_id,      -- Target id (required).
    receivers = { "dmdb" },     -- List of receivers (up to 16).
    requests = {                -- List of requests (up to 8).
      {
        name = "get_values",    -- Request name (required).
        request = "Meter\\r",   -- Raw request to send to sensor.
        delimiter = "\\r",      -- Response delimiter.
        pattern = "^\\s*(?<temp>[-0-9.]+)\\s.C\\s+.t\\s+(?<humrel>[-0-9.]+)\\s%\\s+.t\\s+(?<humabs>[-0-9.]+)\\sg.m3.t\\s+(?<dew>[-0-9.]+)\\s.C\\s+.t\\s+(?<wetbulb>[-0-9.]+)",
        delay = 0,              -- Delay in msec to wait afterwards.
        responses = {           -- List of expected responses.
          { name = "temp",    unit = "degC" }, -- Temperature (real64).
          { name = "humrel",  unit = "%"    }, -- Relative humidity (real64).
          { name = "humabs",  unit = "g/m3" }, -- Absolute humidity (real64).
          { name = "dew",     unit = "degC" }, -- Dew point (real64).
          { name = "wetbulb", unit = "degC" }  -- Wet-bulb temperature (real64).
        }
      }
    }
  }
}

-- Settings of program dmserial. Change the name to the parameter given through
-- command-line argument `--name`.
dmserial = {
  logger = "dmlogger",   -- Name of logger instance (implies log forwarding).
  node = node_id,        -- Sensor node id (required).
  sensor = sensor_id,    -- Sensor id (required).
  output = "",           -- Path of optional output file, or `-` for stdout.
  format = "",           -- Output file format (`csv`, `jsonl`).
  path = "/dev/ttyS0",   -- TTY device path.
  baudrate = 9600,       -- TTY baud rate.
  bytesize = 8,          -- TTY byte size (5, 6, 7, 8).
  parity = "none",       -- TTY parity (`none`, `even`, `odd`).
  stopbits = 2,          -- TTY stop bits (1, 2).
  timeout = 5,           -- TTY timeout in seconds (max. 25).
  dtr = true,            -- TTY Data Terminal Ready (DTR) enabled.
  rts = true,            -- TTY Request To Send (RTS) enabled.
  jobs = {               -- List of jobs to perform.
    {
      -- (1) Start sensor.
      disabled = false,         -- Skip job.
      onetime = true,           -- Run job only once.
      observation = observs[1], -- Observation to perform.
      delay = 2000              -- Delay in msec to wait afterwards.
    },
    {
      -- (2) Stop "Meter Mode".
      disabled = false,         -- Skip job.
      onetime = true,           -- Run job only once.
      observation = observs[2], -- Observation to perform.
      delay = 2000              -- Delay in msec to wait afterwards.
    },
    {
      -- (3) Measure values.
      disabled = false,         -- Skip job.
      onetime = false,          -- Run job only once.
      observation = observs[3], -- Observation to perform.
      delay = 300 * 1000        -- Delay in msec to wait afterwards.
    }
  },
  debug = false,        -- Forward debug messages to logger.
  verbose = true        -- Output debug messages to console.
}

Save the configuration to /opt/etc/dmpack/dmserial.conf.

Monitoring

Start the dmlogger process first:

$ dmlogger --node node-1 --database /opt/var/dmpack/log.sqlite --verbose

Then, start the dmdb database process:

$ dmdb --logger dmlogger --node node-1 --database /opt/var/dmpack/observ.sqlite --verbose

Finally, start dmserial to execute the configured jobs:

$ dmserial --config /opt/etc/dmpack/dmserial.conf

Temperature Sensor (1-Wire)

1-Wire is a half-duplex serial bus designed by Dallas Semiconductor that is typically used to communicate with low-cost digital thermometers and weather stations. This section describes the configuration of DMPACK programs to retrieve temperature values from a single 1-Wire sensor. The following hardware is required:

  • 1-Wire temperature sensor,

  • 1-Wire USB adapter iButtonLink LinkUSB.

Make sure that USB power saving is disabled or the LinkUSB adapter may be detached after a while. The sensor data is read with dmfs and stored to database with dmdb. Additionally, the dmlogger program will capture log messages. The sensor has to be mounted through the virtual 1-Wire File System (OWFS).

1-Wire File System

The 1-Wire File System provides an abstraction layer to access the measurement values of attached sensors. An additional driver is required to mount the virtual file system to which sensors are mapped. On Linux, simply install the OWFS package:

$ sudo apt-get install owfs

Then, connect the temperature sensor via the USB adapter. The device path may be /dev/ttyUSB0 or /dev/ttyU0 depending on the operating system, and will differ if an RS-232 adapter is used instead. Mount the file system with owfs(1) under /mnt/1wire/:

$ sudo mkdir -p /mnt/1wire
$ sudo owfs -C -d /dev/ttyUSB0 --allow_other -m /mnt/1wire

The command-line argument -C selects output in °C. The settings can be added to the owfs(1) configuration file /etc/owfs.conf:

device = /dev/ttyUSB0
mountpoint = /mnt/1wire
allow_other
Celsius

The file system is mounted automatically at system start-up if owfs(1) is configured to run as a service. Read a temperature value from the connected sensor:

$ cat /mnt/1wire/10.DCA98C020800/temperature
19.12

The name of the virtual directory 10.DCA98C020800 depends on the sensor id.

Databases

Once the file system is configured, initialise the observation and log databases with dminit:

$ cd /opt/var/dmpack/
$ dminit --database observ.sqlite --type observ --wal
$ dminit --database log.sqlite --type log --wal

Create node node-1, sensor owfs, and target target-1 in database /opt/var/dmpack/observ.sqlite through dmdbctl:

$ dmdbctl -d observ.sqlite -C node --id node-1 --name "Node 1"
$ dmdbctl -d observ.sqlite -C sensor --id owfs --name "OWFS" --node node-1
$ dmdbctl -d observ.sqlite -C target --id target-1 --name "Target 1"

Configuration

The DMPACK program dmfs will read temperature values periodically from the OWFS and forward observations to dmdb to be saved in the database. Copy the following dmfs configuration to /opt/etc/dmpack/dmfs.conf:

-- dmfs.conf
-- Global identifiers and sensor file path used in the configuration. The
-- identifiers must match the records in the database.
node_id   = "node-1"
sensor_id = "owfs"
target_id = "target-1"
file_path = "/mnt/1wire/10.DCA98C020800/temperature"

dmfs = {
  logger = "dmlogger",          -- Logger to send logs to.
  node = node_id,               -- Node id (required).
  sensor = sensor_id,           -- Sensor id (required).
  output = "",                  -- Path of optional output file, or `-` for stdout.
  format = "none",              -- Output file format (`csv` or `jsonl`).
  jobs = {                      -- List of jobs to perform.
    {
      disabled = false,         -- Skip job.
      onetime = false,          -- Run job only once.
      observation = {           -- Observation to execute (required).
        name = "get_temp",      -- Observation name (required).
        target_id = target_id,  -- Target id (required).
        receivers = { "dmdb" }, -- List of receivers (up to 16).
        requests = {            -- List of files to read.
          {
            request = file_path,              -- File path.
            pattern = "(?<temp>[-+0-9\\.]+)", -- RegEx pattern of the response.
            delay = 500,                      -- Delay in msec to wait afterwards.
            responses = {
              {
                name = "temp",                -- RegEx group name (max. 32 characters).
                unit = "degC",                -- Response unit (max. 8 characters).
                type = RESPONSE_TYPE_REAL64   -- Response value type.
              }
            }
          }
        }
      },
      delay = 10 * 1000,        -- Delay in msec to wait afterwards.
    }
  },
  debug = false,                -- Forward logs of level DEBUG via IPC.
  verbose = true                -- Print messages to standard error.
}

The path /mnt/1wire/10.DCA98C020800/temperature in variable file_path must match the actual file system path of the sensor. The job will be performed every 10 seconds and repeated indefinitely. Log messages are sent to the dmlogger process of default name dmlogger, and observations to the dmdb process of default name dmdb.

Monitoring

Start the dmlogger process first:

$ dmlogger --node node-1 --database /opt/var/dmpack/log.sqlite --verbose

Then, start the dmdb database process:

$ dmdb --logger dmlogger --node node-1 --database /opt/var/dmpack/observ.sqlite --verbose

Finally, start dmfs to execute the configured job:

$ dmfs --config /opt/etc/dmpack/dmfs.conf

UV Sensor (Modbus RTU)

The UV-Cosine is a waterproof and dirt-repellent UV sensor by sglux GmbH, with analog (4–20 mA, 0–5 V, 0–10 V) or digital (USB, Modbus RTU, CAN) output. Depending on the model, the spectral sensitivity of the sensor is calibrated for broadband UV, UVA, UVB+C, UVC, UV index, bluelight, or UV+VI.

For this section, the digital variant with Modbus interface and broadband UV sensitivity is used. See the official Programming Manual on how to programm the UV-Cosine. The sensor uses non-standard Modbus holding register addresses:

Address Name Type Bytes Access Description

100

hardware revision

uint16

2

RD

hardware revision number

101

firmware revision

uint16

2

RD

firmware revision number

104

serial number

uint32

4

RD

sensor serial number

106

sensor address

uint16

2

RDWR

Modbus slave id

107

sensor protocol

uint16

2

RDWR

baud rate, parity, stop bits

110

product vendor

string16

16

RD

vendor name (SGLUX GMBH)

118

product name

string16

16

RD

product name

126

sensor name

string16

16

RDWR

user-defined device name

1030

calibration date

uint32

4

RD

date of calibration

1032

calibration 1

string16

16

RD

name of calibration 1

1040

calibration 2

string16

16

RD

name of calibration 2 (or ?)

1048

calibration 3

string16

16

RD

name of calibration 3 (or ?)

1056

calibration 4

string16

16

RD

name of calibration 4 (or ?)

1064

calibration 5

string16

16

RD

name of calibration 5 (or ?)

2000

cycle count

uint16

2

RD

measurement cycle counter

2001

status

uint16

2

RD

status of ADC

2002

timestamp

uint32

4

RD

internal timestamp [msec]

2004

radiation 1

float

4

RD

radiation by calibration 1 [W/m2]

2006

radiation 2

float

4

RD

radiation by calibration 2 [W/m2]

2008

radiation 3

float

4

RD

radiation by calibration 3 [W/m2]

2010

radiation 4

float

4

RD

radiation by calibration 4 [W/m2]

2012

radiation 5

float

4

RD

radiation by calibration 5 [W/m2]

2014

temperature

float

4

RD

internal sensor temperature [°C]

The radiation in W/m2 (calibration factor 1) is read from register 2004 and the internal temperature in °C from register 2014, both as floating-point number in ABCD byte order. We can test the register access with dmmbctl and output the UV radiation. If the sensor is connected through an USB adapter on /dev/ttyUSB0, run:

$ dmmbctl --path /dev/ttyUSB0 --baudrate 115200 --bytesize 8 --parity even --stopbits 1 \
  --slave 1 --read 2004 --type float --order abcd
1.87749458

The RS-485 interface is configured to the sensor default of 115200 baud (8E1).

Configuration

The Modbus monitoring program dmmb will read radiation and internal temperature from the sensor. The observations are written to /tmp/timeseries.jsonl in JSONL format, without any database storage for simplicity. Copy the dmdb configuration to /opt/etc/dmpack/dmmb.conf:

-- dmmb.conf
dmmb = {
  logger = "",
  node = "node-1",
  sensor = "uv-cosine",
  output = "/tmp/timeseries.jsonl",
  format = "jsonl",
  mode = "rtu",
  rtu = {
    path = "/dev/ttyUSB0",
    baudrate = 115200,
    bytesize = 8,
    parity = "even",
    stopbits = 1
  },
  tcp = {
    address = "127.0.0.1",
    port = 502
  },
  jobs = {
    {
      disabled = false,
      onetime = false,
      delay = 10 * 1000,
      observation = {
        name = "get_values",
        target_id = "target-1",
        receivers = { },
        requests = {
          {
            name = "get_radiation",
            request = "access=read,slave=1,address=2004,type=float,order=abcd",
            responses = {{ name = "radiation", unit = "W/m2" }}
          },
          {
            name = "get_internal_temperature",
            request = "access=read,slave=1,address=2014,type=float,order=abcd",
            responses = {{ name = "temperature", unit = "degC" }}
          }
        }
      }
    }
  },
  debug = false,
  verbose = false
}

Monitoring

Start dmmb to write the measurement values to file /tmp/timeseries.jsonl:

$ dmmb --name dmmb --config /opt/etc/dmpack/dmmb.conf --verbose

Watch the output file:

$ tail -f /tmp/timeseries.jsonl

Weather Station (Modbus RTU)

This section describes the set-up of DMPACK programs to capture sensor data of the digital weather station WSC11 by Adolf Thies GmbH & Co KG. The model used in this example is connected through Modbus RTU to the sensor node. The input registers will be read by the Modbus control program dmmb. All observations are forwarded to dmdb for database storage.

The weather station is offered with RS-485 (ASCII, Modbus RTU) or KNX interface. Depending on the hardware variant, the following values are measured:

  • wind speed and direction;

  • global radiation, twilight, and brightness (north, east, south, west);

  • precipitation status, intensity (option) and amount (option);

  • ice/frost/snow detection (option);

  • temperature and dew point;

  • absolute and relative humidity;

  • absolute air pressure and air pressure at sea level (QNH);

  • sun position, elevation, azimuth;

  • longitude, latitude, and elevation;

  • date and time.

By default, the RS-485 interface of the WSC11 is set to 9600 baud (8N1) with Modbus slave id 1. Change parameter slave in the request strings of the dmdb configuration to the actual slave id.

Databases

In order to store any observations or logs, initialise the databases with dminit first:

$ cd /opt/var/dmpack/
$ dminit --database observ.sqlite --type observ --wal
$ dminit --database log.sqlite --type log --wal

Create node node-1, sensor thies-wsc11, and target target-1 in database /opt/var/dmpack/observ.sqlite through dmdbctl:

$ dmdbctl -d observ.sqlite -C node --id node-1 --name "Node 1"
$ dmdbctl -d observ.sqlite -C sensor --id thies-wsc11 --name "Thies WSC11" --node node-1
$ dmdbctl -d observ.sqlite -C target --id target-1 --name "Target 1"

Optionally, set the sensor type to meteo (for meteorological sensors) with argument --type. Alternatively, the entities can be added with dmweb instead.

Configuration

In this example, the weather station is connected via a WaveShare RS-232/RS-485/TTL converter on /dev/ttyUSB0. The Modbus connection may be tested with dmmbctl first. For instance, read input register 34601 to output the current date in format YYYYMMDD:

$ dmmbctl --path /dev/ttyUSB0 --baudrate 9600 --bytesize 8 --parity none --stopbits 1 \
  --slave 1 --read 34601 --type uint32
20250305

As each observation may contain a maximum of eight requests, reading the input registers is split into multiple observations. Unwanted measurement jobs can simply be disabled. See the user manual (PDF) for an overview of all Modbus registers. The register values are automatically scaled and converted to response type RESPONSE_TYPE_REAL64. The last job does not contain an observation and only causes the program to wait for 60 seconds before the next cycle starts.

The target and the receivers of all observations are declared globally at the top of the file. Copy the dmmb configuration to /opt/etc/dmpack/dmmb.conf if DMPACK is installed to /opt:

-- dmmb.conf
target_id = "target-1"
receivers = { "dmdb" }

dmmb = {
  logger = "dmlogger",
  node = "node-1",
  sensor = "thies-wsc11",
  output = "",
  format = "",
  mode = "rtu",
  rtu = {
    path = "/dev/ttyUSB0",
    baudrate = 9600,
    bytesize = 8,
    parity = "none",
    stopbits = 1
  },
  tcp = {
    address = "127.0.0.1",
    port = 502
  },
  jobs = {
    {
      --
      -- (1) Get wind speed and direction.
      --
      disabled = false,
      onetime = false,
      delay = 0,
      observation = {
        name = "get_wind",
        target_id = target_id,
        receivers = receivers,
        requests = {
          {
            name = "get_wind_speed",
            request = "access=read,slave=1,address=30001,type=uint32,scale=10",
            responses = {{ name = "wind_speed", unit = "m/s" }}
          },
          {
            name = "get_wind_speed_avg",
            request = "access=read,slave=1,address=30003,type=uint32,scale=10",
            responses = {{ name = "wind_speed_avg", unit = "m/s" }}
          },
          {
            name = "get_wind_dir",
            request = "access=read,slave=1,address=30201,type=uint32,scale=10",
            responses = {{ name = "wind_dir", unit = "deg" }}
          },
          {
            name = "get_wind_dir_avg",
            request = "access=read,slave=1,address=30203,type=uint32,scale=10",
            responses = {{ name = "wind_dir_avg", unit = "deg" }}
          }
        }
      }
    },
    {
      --
      -- (2) Get temperature, humidity, and air pressure.
      --
      disabled = false,
      onetime = false,
      delay = 0,
      observation = {
        name = "get_temp_hum_press",
        target_id = target_id,
        receivers = receivers,
        requests = {
          {
            name = "get_temperature",
            request = "access=read,slave=1,address=30401,type=int32,scale=10",
            responses = {{ name = "temperature", unit = "degC" }}
          },
          {
            name = "get_internal_temperature",
            request = "access=read,slave=1,address=30403,type=int32,scale=10",
            responses = {{ name = "internal_temperature", unit = "degC" }}
          },
          {
            name = "get_relative_humidity",
            request = "access=read,slave=1,address=30601,type=uint32,scale=10",
            responses = {{ name = "rel_humidity", unit = "%rh" }}
          },
          {
            name = "get_absolute_humidity",
            request = "access=read,slave=1,address=30603,type=uint32,scale=100",
            responses = {{ name = "abs_humidity", unit = "g/m3" }}
          },
          {
            name = "get_dew_point",
            request = "access=read,slave=1,address=30605,type=int32,scale=10",
            responses = {{ name = "dew_point", unit = "degC" }}
          },
          {
            name = "get_absolute_pressure",
            request = "access=read,slave=1,address=30801,type=uint32,scale=100",
            responses = {{ name = "abs_pressure", unit = "hPa" }}
          },
          {
            name = "get_relative_pressure",
            request = "access=read,slave=1,address=30803,type=uint32,scale=100",
            responses = {{ name = "rel_pressure", unit = "hPa" }}
          }
        }
      }
    },
    {
      --
      -- (3) Get global radiation, brightness, and sun position.
      --
      disabled = false,
      onetime = false,
      delay = 0,
      observation = {
        name = "get_radiation",
        target_id = target_id,
        receivers = receivers,
        requests = {
          {
            name = "get_global_radiation",
            request = "access=read,slave=1,address=31001,type=int32,scale=10",
            responses = {{ name = "radiation", unit = "W/m2" }}
          },
          {
            name = "get_brightness_north",
            request = "access=read,slave=1,address=31201,type=uint32,scale=10",
            responses = {{ name = "bright_north", unit = "kLux" }}
          },
          {
            name = "get_brightness_east",
            request = "access=read,slave=1,address=31203,type=uint32,scale=10",
            responses = {{ name = "bright_east", unit = "kLux" }}
          },
          {
            name = "get_brightness_south",
            request = "access=read,slave=1,address=31205,type=uint32,scale=10",
            responses = {{ name = "bright_south", unit = "kLux" }}
          },
          {
            name = "get_brightness_west",
            request = "access=read,slave=1,address=31207,type=uint32,scale=10",
            responses = {{ name = "bright_west", unit = "kLux" }}
          },
          {
            name = "get_twilight",
            request = "access=read,slave=1,address=31209,type=uint32,scale=1",
            responses = {{ name = "twilight", unit = "Lux" }}
          },
          {
            name = "get_sun_elevation",
            request = "access=read,slave=1,address=34805,type=int32,scale=10",
            responses = {{ name = "sun_elevation", unit = "deg" }}
          },
          {
            name = "get_sun_azimuth",
            request = "access=read,slave=1,address=34807,type=int32,scale=10",
            responses = {{ name = "sun_azimuth", unit = "deg" }}
          }
        }
      }
    },
    {
      --
      -- (4) Get GPS position (longitude, latitude, elevation in NN/NHN).
      --
      disabled = false,
      onetime = false,
      delay = 0,
      observation = {
        name = "get_position",
        target_id = target_id,
        receivers = receivers,
        requests = {
          {
            name = "get_longitude",
            request = "access=read,slave=1,address=34801,type=int32,scale=1000000",
            responses = {{ name = "longitude", unit = "deg" }}
          },
          {
            name = "get_latitude",
            request = "access=read,slave=1,address=34803,type=int32,scale=1000000",
            responses = {{ name = "latitude", unit = "deg" }}
          },
          {
            name = "get_elevation_nn",
            request = "access=read,slave=1,address=34809,type=uint32,scale=1",
            responses = {{ name = "elevation_nn", unit = "m" }}
          },
          {
            name = "get_elevation_nhn",
            request = "access=read,slave=1,address=34817,type=uint32,scale=10",
            responses = {{ name = "elevation_nhn", unit = "m" }}
          },
        }
      }
    },
    {
      --
      -- (5) Wait 60 seconds.
      --
      disabled = false,
      onetime = false,
      delay = 60 * 1000
    }
  },
  debug = false,
  verbose = false
}

Monitoring

Start the dmlogger process to store any logs:

$ dmlogger --node node-1 --database /opt/var/dmpack/log.sqlite --verbose

Start the dmdb database process to store the observations:

$ dmdb --logger dmlogger --node node-1 --database /opt/var/dmpack/observ.sqlite --verbose

Start dmmb to execute the configured jobs:

$ dmmb --name dmmb --config /opt/etc/dmpack/dmmb.conf --verbose

Digital Multimeter (RS-232)

PeakTech 4094
Figure 9. PeakTech 4094 digital multimeter

Digital multimeters are used to measure values like voltage, resistance, current, and temperature. If equipped with a serial interface, modern devices are even programmable through protocols like SCPI.

In this example, the voltage of a 24 VDC power supply unit is monitored using a PeakTech 4094 graphical bench multimeter. The multimeter features an RS-232 interface and SCPI protocol support. The voltage values will be read by dmserial, forwarded to dmrecv, and displayed as a trend graph without additional persistence. The serial port is configured to the default parameters of the device (11500 baud, 8N1). The 50 VDC measurement function has to be selected using the keys on the front panel or via the SCPI command SENSe:FUNCtion. See the official programming manual (PDF) for an overview of supported SCPI commands.

The captured voltage is filtered by GNU awk first and then rendered with trend. On Linux, install the required packages first:

$ sudo apt-get install gawk trend

Configuration

The multimeter is attached to /dev/ttyUSB0. The sensor control program dmserial will send the measurement command MEAS1? once every second to the PeakTech 4094 to read the voltage, then forward the observation to dmrecv for plotting. Values are usually returned in scientific notation. Therefore, the regular expression pattern for response extraction has to include the character E.

-- dmserial.conf
dmserial = {
  logger = "",                      -- Name of logger instance (implies log forwarding).
  node = "node-1",                  -- Sensor node id (required).
  sensor = "peaktech-4094",         -- Sensor id (required).
  output = "",                      -- Path of optional output file, or `-` for stdout.
  format = "",                      -- Output file format (`csv`, `jsonl`).
  path = "/dev/ttyUSB0",            -- TTY device path.
  baudrate = 115200,                -- TTY baud rate.
  bytesize = 8,                     -- TTY byte size (5, 6, 7, 8).
  parity = "none",                  -- TTY parity (`none`, `even`, `odd`).
  stopbits = 1,                     -- TTY stop bits (1, 2).
  timeout = 0,                      -- TTY timeout in seconds (max. 25).
  dtr = false,                      -- TTY Data Terminal Ready (DTR) enabled.
  rts = false,                      -- TTY Request To Send (RTS) enabled.
  jobs = {                          -- List of jobs to perform.
    {
      disabled = false,             -- Skip job.
      onetime = false,              -- Run job only once.
      observation = {               -- Observation to execute.
        name = "meter",             -- Observation name (required).
        target_id = "target-1",     -- Target id (required).
        receivers = { "dmrecv" },   -- List of receivers (up to 16).
        requests = {
          {
            name = "get_voltage",                -- Request name (required).
            request = "MEAS1?\\r\\n",            -- Raw request to send to sensor.
            delimiter = "\\r\\n",                -- Response delimiter.
            pattern = "^(?<voltage>[-+.0-9E]+)", -- RegEx pattern of the response.
            delay = 0,                           -- Delay in msec to wait afterwards.
            responses = {                        -- List of expected responses.
              {
                name = "voltage",                -- RegEx group name (max. 32 characters).
                unit = "VDC",                    -- Response unit (max. 8 characters).
                type = RESPONSE_TYPE_REAL64      -- Response value type.
              },
            }
          }
        }
      },
      delay = 1000                  -- Delay in msec to wait afterwards.
    }
  },
  debug = false,                    -- Forward logs of level DEBUG via IPC.
  verbose = false                   -- Print messages to standard error.
}

Additionally, we can add a job to select the measurement function via SCPI before starting observation meter (for instance, AC/DC voltage, AC/DC current, frequency, or resistance).

Monitoring

Start dmserial and pass the path to the configuration file as a command-line argument:

$ dmserial --name dmserial --config config/dmserial.conf --verbose

The program dmrecv will print responses of name voltage in ASCII block format to standard output. gawk(1) then extracts the response value and pipes it to trend(1):

$ dmrecv --name dmrecv --type observ --format block --response voltage \
  | gawk '{ print $2 | "trend - 60" }'

The trend graph is rendered in real-time with OpenGL.

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