Example CoMatrix Temperature Sensor

A prototype application, which illustrates a simple use case of a temperature sensor node (SAMR21-xpro + DS18S20) that sends temperature data into a pre-configured Matrix room using the CoMatrix client library.

Hardware:

• A DS18S20 temperature sensor and a 4,7 kohm resistor
• A SAMR21-xpro

DS18S20 temperature sensor

• Datasheet: https://datasheets.maximintegrated.com/en/ds/DS18S20.pdf

SAMR21-xpro

• Datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-42243-SAMR21-Xplained-Pro_User-Guide.pdf

Important: The DQ of DS18S20 sensor needs to be connected to a GPIO Pin, in our case we used PA14 and over a 4,7 kohm resistor to the VCC on the SAMR21-xpro.

Connect Pinout:

DS18S20                          4,7 kohm resistor           SAMR21-xpro
GND (left pin of DS18S20)    ->         ->             ->   GND  (Ext3 19 on SAMR21-xpro)
DQ  (middle pin of DS18S20)  ->  4,7 kohm (left pin)   ->   PA14 (Ext3 15 on SAMR21-xpro)
VDD (right pin of DS18S20)   ->  4,7 kohm (right pin)  ->   VCC

Preliminaries

• Tested environment
  • Code tested on a SAMR21-xpro microcontroller with RIOT OS (Release-2021.04,tag 46bc55f514).
  • Tested toolchain: GNU Arm Embedded Toolchain 9-2020-q2-update
• Setup
  • Reqirements: Running CoMatrix Gateway and Matrix-Synapse homeserver (Follow the steps in the setup tutorial)
  • Copy the Client folder into the RIOT/example/ folder of your RIOT base directory.

Client Configuration

The application specific settings need to be set in an app.config file, consider the app.config.example.

• Synapse endpoint (e.g. CONFIG_COMATRIX_SYNAPSE="http://192.168.1.1:8008")
• Gateway link-local IPv6 address (e.g. CONFIG_COMATRIX_GATEWAYIP6="fe80::1")
• Matrix room ID (e.g. CONFIG_COMATRIX_ROOMID="!kYsGiNgnRRVZCizHAF:synapse")
• Synapse user specific access token (e.g. CONFIG_COMATRIX_TOKEN="MDAxNWxvY...")
• Default 6LoWPAN and WPAN settings:
  • default WPAN channel: 26
  • default 6LoWPAN PANID: 0x23

Compilation

Change to the application root folder (RIOTBASE/example/Client/example_comatrix_tempsensor) and build the application via make for the samr21-xpro board and flash the binary firmware on the microcontroller:

make BOARD=samr21-xpro
make BOARD=samr21-xpro flash

Enable serial communication over an USB cable between SAMR21-xpro and a PC using pyterm (python -m pip install pyterm) and connect to the SAMR21-xpro:

make BOARD=samr21-xpro term

Usage

If valid parameters are set (Synapse access token, Matrix room ID and Matrix-Synapse homeserver endpoint and CoMatrix gateway address) the application will send temperature values into the specified Matrix room each minute, immediately after starting. Stop sending messages with the sendtemp stop command.

Available application specific commands are:

• readtemp: Reads and prints temperature value from DS18S20 temperature sensor.

usage: readtemp

• sendtemp: Start and stop the thread that continuously sends temperature values into the configured Matrix room.

usage: sendtemp <start|stop>

Future work

• Enable encryption of the communication to the gateway either via DTLS support, OSCORE or OpenThread.
• Modify sendtemp thread that only on temperature change a message is sent into a room (these messages are so annoying:)).