rtndf now has Python PPEs that support streaming data from a variety of environmental sensors. The sensehat PPE streams data from all of the sensors on the Raspberry Pi Sense HAT. The sensors PPE streams data from a variety of common environmental sensors:
BMP180 pressure/temperature sensor
HTU21D humidity sensor
MCP9808 temperature sensor
TMP102 temperature sensor
TSL2561 light sensor
The specific sensors in use can be enabled by selectively commenting out lines in the sensors Python script.
sensorview is another new PPE that can display the sensor streams generated by sensehat and sensors. The screenshot shows the data from a sensehat for example.
Up to now the only data sources in rtndf were video and audio. imu is a new Python PPE that can be used to stream IMU data (fused pose, sensor readings etc) into an rtndf data flow pipeline. Another new PPE is imuview, this time a C++ PPE, that can display the resulting stream. The screen capture above shows the data being streamed from a Raspberry Pi SenseHat which is a full 11-dof sensor.
One of the nice things about using a pub/sub system like MQTT is that it is possible to hook into any of the pipeline links to see what data is flowing. To this end, a future PPE will be a generic viewer. The user just gives it the topic and it determines the type of data and displays it appropriately. A very handy debugging tool!
The idea of joining together separate, lightweight processing elements to form complex pipelines is nothing new. DirectX and GStreamer have been doing this kind of thing for a long time. More recently, Apache NiFi has done a similar kind of thing but with Java classes. While Apache NiFi does have a lot of nice features, I really don’t want to live in Java hell.
I have been playing with MQTT for some time now and it is a very easy to use publish/subscribe system that’s used in all kinds of places. Seemed like it could be the glue for something…
So that’s really the background for rtnDataFlow or rtndf as it is now called. It currently uses MQTT as its pub/sub infrastructure but there’s nothing too specific there – MQTT could easily be swapped out for something else if required. The repo consists of a number of pipeline processing elements that can be used to do some (hopefully) useful things. The primary language is Python although there’s nothing stopping anything being used provided it has an MQTT client and handles the JSON messages correctly. It will even be able to include pipeline processing elements in Docker containers. This will make deployment of new, complex, pipeline processing elements very simple.
The pipeline processing elements are all joined up using topics. Pipeline processing elements can publish to one or more topics and/or subscribe to one or more topics. Because pub/sub systems are intrinsically multicasting, it’s very easy to process data in multiple ways in parallel (for redundancy, performance or functionality). MQTT also allows pipeline processing elements to be distributed on multiple systems, allowing load sharing and heterogeneous computing systems (where only some machines might be fitted with GPUs for example).
Obviously, tools are required to design the pipelines and also to manage them at runtime. The design aspect will come from an old code generation project. While that actually generates C and Python code from a design that the user inputs via a graphical interface, the rtnDataFlow version will just make sure all topic names and broker addresses line up correctly and then produce a pipeline configuration file. A special app, rtnFlowControl, will run on each system and will be responsible for implementing the pipeline design specified.
So what’s the point of all of this? I’m tired of writing (or reworking) code multiple times for slightly different applications. My goal is to keep the pipeline processing elements simple enough and tightly focused so that the specific application can be achieved by just wiring together pipeline processing elements. There’ll end up being quite a few of these of course and probably most applications will still need custom elements but it’s better than nothing. My initial use of rtnDataFlow will be to assist with experiments to see how machine learning tools can be used with IoT devices to do interesting things.