The Ware for July 2020 was a PocketVNA. Congrats to Jean for nailing it! email me for your prize. I acquired a PocketVNA a little while ago to try and tune some antenna for the Betrusted project. It has some quirks and limitations, but for the price it was a good value for the capabilities it brings.
Winner, Name that Ware July 2020
August 31st, 2020Name that Ware, July 2020
July 31st, 2020The Ware for July 2020 is shown below.
This ware is ever so slightly cropped to hide the connectors on the edges, which would make it way too easy to guess.
Winner, Name that Ware June 2020
July 31st, 2020The Ware for June 2020 is an Elcotel Series 5 payphone. Apparently it was found vandalized in a parking lot, and so a few pictures of its insides were able to find its way to me via Bob Parker (thank you!). I always wondered what was inside these payphones, now I know. Gratz again to jackw01 for nailing it, email me for your prize!
On Liberating My Smartwatch From Cloud Services
July 25th, 2020I’ve often said that if we convince ourselves that technology is magic, we risk becoming hostages to it. Just recently, I had a brush with this fate, but happily, I was saved by open source.
At the time of writing, Garmin is suffering from a massive ransomware attack. I also happen to be a user of the Garmin Instinct watch. I’m very happy with it, and in many ways, it’s magical how much capability is packed into such a tiny package.
I also happen to have a hobby of paddling the outrigger canoe:
Paddled around the island of Hong Kong in an outrigger canoe “change race” for the 2018 #RHKYCATIR event! Stunning coastline and an unbeatable harbor view. Impressed at how @RHKYC pulled it off even after the typhoon devastated a lot of their equipment.
A Near-Ultrasound (NUS) Data Link
July 8th, 2020We were requested to investigate “near ultrasound” (NUS) links as part of our research on developing the Simmel reference design for a privacy-preserving COVID-19 contact tracing device. After a month of poking at it, the TL;DR is that, as suspected, the physics of NUS is not conducive to reliable contact tracing. While BLE has the problem that you have too many false positive contacts, NUS has the problem of too many false negatives: pockets, purses, and your own body can effectively block the signal.
That being said, we did develop a pretty decent-performing NUS data link, so we’ve packed up what we did into an open source reference design that you can clone and use in your own projects.
Top trace: demodulated data at 1 meter, 50dB background noise. Bottom trace: raw signal, normalized so it is visible. Without normalization the trace just looks like a flat line.
I imagine one use for this would be a way to provision IoT devices: the “how do I get wifi credentials into an IoT device that lacks both screen and keyboard?” problem. With the addition of a ~$1 microphone to a Cortex-M4 class device, you get a short-range data link to a host device, such as a phone. You can use a web page (via Javascript) to generate the modulated audio directly (relevant example), thus bypassing a host of multi-platform issues, or you can generate a file off-line and send it to any standard music player.
The TL;DR on the link is it uses a 20,833Hz carrier modulated with BPSK. We use PSK31 coding, so our baud rate is ~651 symbols per second (this is the 1/0 symbol rate before Varicode encoding). This isn’t breaking any speed records, but it’s good enough to send a UUID and some keys over the air in a couple seconds. Tests show decent performance over a distance of 1 meter with about 60dB ambient noise (normal conversation or background music playing at the same time).
The demodulator uses a Costas loop. We’ve documented its details, including comments on porting to other chipsets than the NRF52.
We also have a reference modulator using a non-linear transducer (e.g. a piezo element), which uses some of the more advanced features of the NRF52 PWM block to eliminate audible sidebands. We also have a rough C program to generate a .wav file, which needs to be run through a high-pass filter using e.g. Audacity to eliminate the low-frequency modulation sidebands; but the resulting .wav file can be played directly on your smartphone and it will demodulate correctly.
Acknowledgements: Sean ‘xobs’ Cross is an equal contributor to this research. This research is funded through the NGI0 PET Fund, a fund established by NLnet with financial support from the European Commission’s Next Generation Internet programme, under the aegis of DG Communications Networks, Content and Technology under grant agreement No 825310.