Aircraft Traces

One of my trusty Raspberry Pis has a SDR (Software Defined Radio) USB stick, which is currently tuned into aircraft ADS-B transponders (which basically means that the Pi receives the position, altitude, speed and heading of every commercial aircraft within 50-100km, sometimes up to 200km, if the conditions are right).

The Pi now logs this data every 10 seconds to a file, which I copied from the Pi this evening and with a bit of Groovy scripting was able to generate the traces of aircraft seen over the last 8 hours or so:

You can clearly see the Lambourne, Biggin and Ockham holding stacks, where the planes circle around for a while, descending until given a landing slot.

The aircraft disappear from my screen below 1500ft or so, which is why you can see lots of planes approaching Heathrow (from the east/right) but they all seem to disappear before they get there. Similarly with Gatwick, many aircraft disappear from the right (east) as they arrive and many appear to the left (west) as they leave.

The data and processing isn’t perfect, but it’s a pretty picture for now. :)

Raspberry Pi – AnswerBox

I’ve been playing with a Raspberry Pi, Logitech USB mic, USB-powered speakers and a USB SDR TV tuner stick, combined with Stephen Hickson’s fantastic voicecommand system. (The Pi is the rainbox-striped box at the back, the flat black thing in the middle is a powered USB hub, into which is plugged the black TV tuner stick, which has an aerial (positioned on the small jar). The Rubix Cube is just there for scale.)

First, speech is sent as raw audio to a Google API which returns text. It would be better to do this on the Pi, but my experiments (with Julius) have shown that Google (with their gargantuan computing grid) is much better in terms of both speed and accuracy. (Since the microphone has an on/off button, audio is only sent to Google when I so choose.)

Second, the text is compared with a list of known commands (see the voicecommand website for more details). If a match is found, the corresponding script is run. (This is how the ‘weather forecast’ and ‘have I got mail’ commands work.) If no match is found, the text is sent off to Wolfram Alpha, which returns a text answer.

Finally, the results from Wolfram Alpha, or the appropriate script, are sent off to another Google API to turn them into an audio file, which is then played out over the speakers. I have tried using espeak, but again, Google’s API currently does a better job.

The whole thing is reasonably fast, given everything that is involved. Occasional internet latency spikes delay responses from the script for 10 seconds or so, but in my experience they are rare.

The live aircraft information is received using the Software Defined Radio (SDR) technique, using a RTL2838 TV tuner USB stick with rtl-sdr and dump1090 software, which provides a nice json interface over http. A python script queries this interface on demand and computes the nearest couple of aircraft to my location, then gathers some supplementary information from the internet before reading the response.

The scripts that make all this work are available on github.

Future plans include: adding commands to play music, add items to a shopping list, read news headlines and much more. My four year old daughter’s most recent request was for the AnswerBox to gain wings and fly around the room on request. There’s probably a python library for that. Hmmm….

Dansette