6. Remote Monitoring Radio Frequency Broadcast

Greenhouse automation system remote monitoring radio frequency broadcast

Python script for VOX activated radio frequency broadcast transmissions containing audible voice and data notifications of greenhouse environmental conditions on an Ubuntu 18 desktop

Warning: Laws governing the operation of radio frequency transceiver or transmitter are clearly established by legal regulations globally. Ensure any radio frequency broadcasts performed are done so within the legally acceptable national guidelines of your region.

Data Flow Diagram

Prerequisites

• Non-interactive network downloader (wget)

• Ubuntu speech-dispatcher (spd-say)

• Desktop notification application (notify-send)

• General-purpose software audio FSK modem (minimodem)

• Cross-platform command line audio manipulation utility (sox)

• Python 3

• Python classes for generating Slow-scan Television transmissions (PySSTV)

$ sudo apt install python3-pip

$ sudo python3 -m pip install PySSTV

Produces

• Desktop visual notification "bubble"

• Text-to-speech audio containing greenhouse environmental data

• RTTY audio data output containing greenhouse environmental data

• SSTV audio data output containing an image from the greenhouse interior camera

greenhousestatusttsrttysstvrf.py is a Python script that retrieves the latest greenhouse environmental data produced by /Greenhouse/greenhouse.py in CSV format and camera image data produced by /Greenhouse/camera.py and produces a desktop notification, text-to-speech audio output, RTTY data output, and SSTV data output.

The audio output produced by greenhousestatusttsrttysstvrf.py can be connected to a radio in VOX (voice-operated exchange) mode allowing for radio frequency transmission of the current greenhouse environmental conditions.

Before transmitting on any channel or frequency the channel should be monitored for at least 30 seconds to verify that the channel is clear/available.

greenhousestatusttsrttysstvrf.py uses SoX to achieve verification of the current channels availability. SoX is used to record a 30 second sample of the current channel. SoX is then used to generate statistics from the audio recording to establish a maximum amplitude value. This maximum amplitude value is used to determine if the current broadcast should be deferred due to traffic on the channel or frequency. A maximum amplitude value > 0.025 is indicative of audio input/channel traffic. The maximum amplitude value may have to be adjusted relative other systems audio sample configurations. Please note that on some system configurations calculating the midline amplitude value may be more useful for detecting audio input than the maximum amplitude value.

Crontab script execution

To execute greenhousestatusttsrttysstvrf.py using a cron tab use a bash shell script wrapper that exports environmental variables to the Python script. Access to environmental variables allow applications to access the desktop GUI and specific users audio output devices. (e.g. notify-send, spd-say).

Reference

https://askubuntu.com/questions/978382/how-can-i-show-notify-send-messages-triggered-by-crontab

https://askubuntu.com/questions/719590/help-using-crontab-to-play-a-sound

# Example bash shell script gui-launcher wrapper contents
!#!/bin/bash -e

NAME: gui-launcher

Check whether the user is logged-in

while [ -z "$(pgrep gnome-session -n -U $UID)" ]; do sleep 3; done

!# Export the current desktop session environment variables

export $(xargs -0 -a "/proc/$(pgrep gnome-session -n -U $UID)/environ")

export XDG_RUNTIME_DIR="/run/user/1000"

export $(egrep -z DBUS_SESSION_BUS_ADDRESS /proc/$(pgrep -u $LOGNAME gnome-session)/environ)

!# Execute the input command

nohup "$@" >/dev/null 2>&1 &

exit 0

Example greenhousestatusttsrttysstvrf.py execution via the bash shell wrapper script gui-launcher using a crontab executed every 20th minute

*/20 * * * * /home/username/gui-launcher "/home/username/greenhousestatusttsrttysstvrf.py"

Proceed to next section: Section 7. Remote Monitoring Radio Frequency Reception