Single sawtooth signal#

The characteristics of sawtooth signals (dynamic, slowly oscillating) are convenient to generate measurement sensor readings and publish telemetry data without having any hardware in place.

Sawtooth signal with MQTT#

Prerequisites#

The following examples depend on mosquitto_pub usually contained in the mosquitto-clients distribution package or similar:

# Setup "mosquitto_pub"
aptitude install mosquitto-clients

Sensor#

Let’s define a an example sensor emitting a single sawtooth signal:

# Define an example sensor emitting a single sample of a sawtooth signal in JSON format
sensor() { echo "{\"sawtooth\": $(date +%-S)}"; }

Check if the sensor works properly:

# Read sensor value
sensor
{"sawtooth": 42}

# Verify it's actually JSON
sensor | python -mjson.tool
{
    "sawtooth": 42
}

Transmitter#

Get real and actually transmit sensor values to Kotori by publishing them to the MQTT bus:

# Where to send data to
export MQTT_BROKER=kotori.example.org
export MQTT_TOPIC=mqttkit-1/testdrive/area-42/node-1

# Define the transmission command to send telemetry data to the "testdrive" network
transmitter() { mosquitto_pub -h $MQTT_BROKER -t $MQTT_TOPIC/data.json -l; }

# Acquire and transmit a single sensor reading
sensor | transmitter

Periodic transmitter#

“hands-free”, periodic dry-dock measurements:

measure() { sensor | transmitter; }
loop() { while true; do measure; echo -n .; sleep 1; done; }

Start publishing:

loop

Result#

Sawtooth signal made from oscillating value of current second.

In /var/log/kotori/kotori.log, you should see things like:

2016-05-27T03:03:58+0200 [kotori.daq.services.mig            ] INFO: [mqttkit-1   ] transactions: 1.00 tps

Sawtooth signal with HTTP#

Same as above for MQTT, but with slightly changed transmitter.

Prerequisites#

This example depends on HTTPie:

aptitude install httpie

Transmitter#

# Define transmitter
transmitter() { http POST http://localhost:24642/api/$DEVICE_TOPIC/data; }

Result#

Sawtooth signal made from oscillating value of the current second.

Multiple sawtooth signals#

A more advanced sensor might be:

# Let's define multiple sawtooth signals, also derived from current time
sensor() { jo second=$(date +%-S) minute=$(date +%-M) hour=$(date +%-H) day=$(date +%-d) month=$(date +%-m); }

Check if the sensor works properly:

# Read sensor values
sensor | python -mjson.tool
{
    "day": 27,
    "hour": 2,
    "minute": 37,
    "month": 5,
    "second": 45
}

Restart transmitting:

loop

Result:

Whole date of second, minute, hour, day and month.

Note

This uses the jo tool by Jan-Piet Mens to format a JSON message on the command line, see also:

There are source release archives and windows binaries:

https://github.com/jpmens/jo/releases

as well as distribution packages for Debian-based systems, e.g.: