Arduino sensor web interface

TODO list

• Send scales along with points

Installing

Clone the repository to your hard disk, and then cd into the newly created folder.

The Arduino code

A sample Arduino sketch is provided (sinewave_generator.ino). It simply generates a sine wave and outputs it over serial in the expected format for readings. Useful for debugging only!

Download and install the official Arduino IDE here https://www.arduino.cc/en/main/software to modify, compile and upload the code to your Arduino board. Follow the guide here for more details.

An Arduino running the provided sketch (or any other valid sketch that communicates in the expected manner with the listener) is NOT required to test the web interface. A dummy listener class is provided to simulate the reception of data.

The web interface

You’ll need to generate and activate a python3 virtual environment:

$ python3 -m venv ./venv
$ source venv/bin/activate

You’ll know that the virtual environment is active when your prompt is prefixed by (venv). To exit the virtual environment simply type

(venv) $ deactivate

Install the required dependencies within your virtual environment:

(venv) $ pip install -r requirements.txt

Now you can finally launch the webserver:

(venv) $ ./webserver.py

To view the webpage in your browser, open http://0.0.0.0:5000 in your web browser.

Usage

Serial protocol

The protocol used for this package is a simple handshake-based json interface. The Arduino probes for a listener by sending 0x41 bytes at regular intervals, waiting to receive the same byte in response. Once this handshake established, the Arduino periodically sends sensor data formatted as a line of JSON, as follows:

[
    {"stream":"aStreamName","value":42},
    {"stream":"anotherStreamName","value":420}
]

Each line is an array of points, and each point is an object containing a stream name and a value. Each point gets attributed a timestamp on reception by the listener. The connection is terminated when the Arduino receives a 0x00 byte, which makes it return to the probing state.

These bytes can be easily changed: in listener.py they are defined as default values for the Listener class. You can simply create your instance with different values:

class Listener(Thread):
    def __init__(
        self,
        queue,
        port,
        baudrate,
        db_name,
        handshake_byte=b"\x41",
        close_byte=b"\x00",
        interval=1, 
        realtime=False
    ):

Similarly, in the Arduino sketch these constants are defined as macros at the top of the file:

#define HANDSHAKE_BYTE      0x41
#define CLOSE_BYTE          0x00

Web server / client communication

The client can request intervals of data via XHR POST requests or open an event stream with the server. In the case of an XHR, the server will respond with a JSON array that contains all the requested points obtained from the SQLite database. In the case of an event stream, the server sends the client JSON arrays every time it receives a new point from the listener via the global queue.

New points aren't always added to the queue: on creation of an event stream, we set the listener's realtime property to True, at witch point it starts adding new points to the queue as well as the SQLite database. This property is set back to False on reception of an XHR requesting historical points.

Authors

• Dylan Robins - https://github.com/dylan-robins
• Joris Placette - https://github.com/JorisPLA7

License

This project is licensed under the GNU GPLv3 - see the LICENSE file for details