Get sensor data over the serial line and send it to an URL (JSON).
Python library to report back the sensor data from, e.g., our arduino(s).
See https://github.com/zwischenloesung/ardu-report for a CLI using it.
- Python 2.7, 3.3, 3.4, 3.5
- see requirements.txt for the dependencies
- Upload to PyPI
There is a central data store that holds the data. It accepts JSON as input and returns JSON. Both in- and output JSON can be specified by a JSON Schema (see below).
One or more reader threads can be connected to one or more serial lines to collect the data from the microcontroller connected to the actual sensors. Whenever data is sent over the wire, it is then stored in the data store object described above.
A third reporter object can then be told to report the data on a regular basis to some URL.
Import and Setup
See https://github.com/zwischenloesung/ardu-report for a concrete example implementation.
Import the classes:
from libardurep import datastore, datareporter, serialreader
Create the objects (example):
store = datastore.DataStore() url = 'file:///tmp/example' reporter = datareporter.DataReporter(store, url) rounds = 10 device = '/dev/ttyACM0' baudrate = 9600 reader = serialreader.SerialReader(device, baudrate, store, rounds)
Does It Make Sense for Your Project?
As we really only need some sort of identifier and a value, for a valid sensor datum, it is quite trivial to accept a wide range of input JSON as provided by the sensor infrastructure and to be able to transform it to some output JSON as needed by your display infrastructure.
There is a meta schema definition in the ‘schema’ folder that describes the valid schemas. Any such valid schema can be provided to the data store object to describe the JSON expected to come from the sensor infrastructure and equally for the JSON that is desired as output. Load the custom schema on DataStore creation like:
datastore.DataStore(input_schema, input_meta_schema, output_schema, output_meta_schema)
The ‘example’ folder contains JSON file that validates against the schema and the tests/test_json.py has a test run for both the input.json against the schema and the schema against the meta-schema.. Furthermore there is an extended-input.json that validates against an example customized schema (extended-input-schema.json), with itself still validates against the meta-schema.json.
Example Data for Python Processing
INPUT: JSON from the (e.g.) arduino over the serial line
There are two examples under the ‘examples’ folder.
The simple ‘input.json’ shows two example measurements. The “id” and “value” entries in the object are mandatory. The “unit” and “threshold” are recognized (and interpreted for the text form output to stdout, see the datastore code for details).
Note that no timestamp joins the data. Often there is no clock source available to the dump sensor controller. The timestamp is added in the output below though. If a timestamp is available in the input though, it can still be passed on of course.
See the ‘extended-input.json’ for an example with more enries and custom naming.
OUTPUT: Target JSON from the (e.g.) raspberry pi for the use in e.g. a web app
The data is appended to a file (“file://”) as a continuing list of JSON objects containing sensor value entries or sent as a complete JSON array to a web server (“http://” / “https://”) as a POST request. Alternatively the data is just printed in text form to stdout.
Example JSON output can be found under the examples folder:
- output.json - default
- custom-output.json - if an output JSON scheme is defined, the entries can be translated. The output JSON must validate against the meta schema..
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