Decimation

At the time of this writing, the James Webb Space Telescope was perched upon its ride to space, ready for its much-delayed launch from the ESA spaceport in French Guiana. The $10 billion space observatory suffered one final delay (knocks on wood) when predictions of high winds aloft pushed it back from a Christmas Eve launch to a Christmas Day departure, at 12:20 UTC. Given the exigencies of the day, we doubt we’ll be able to watch the launch live — then again, past experience indicates we’ll still be wrapping presents at 4:20 PST. Either way, here’s hoping that everything comes off without a hitch, and that astronomers get the present they’ve been waiting many, many Christmases for.

In other space news, things are getting really interesting on Mars. The ESA announced that their ExoMars Trace Gas Orbiter has detected signs of water in the Valles Marineris. The satellite found a large area of increased hydrogen concentration in the top meter of Martian soil; the assumption is that the hydrogen comes from water, meaning that as much as 40% of the material in the region scanned may be water. If so, that’s a huge find, as we thought most of Mars’ water was locked in the polar regions. The Mariner Valley stretches more than 4,000 km just below the equator, and so may prove to be an important resource for future explorers.

Meanwhile, in Jezero crater, Perseverance has decided to upstage its rotorcraft sidekick for a change by finding signs of organic molecules on Mars. It’s not the first time organic compounds have been found — Perseverance’s cousin Curiosity found some too, ESA’s Mars Express mission spotted methane from on high, and then there were the equivocal but intriguing results from the Viking missions in the 1970s. But the latest evidence is really great news for the scientists who picked Jezero crater as a likely place to search for signs of past life on Mars. The organics found are not proof of life by any means, as there are many ways to make organic molecules abiotically. But then again, if you’re going to find evidence of life on Mars, you’ve got to start with detecting organics.

Back on Earth, getting your laptop stolen would be bad enough. But what if it got yoinked while it was unlocked? Depending on who you are and what you do with that machine, it could be a death sentence. That’s where BusKill could come in handy. It’s a hardware-software approach to securing a laptop when it — or you — suddenly goes missing. A dongle with a breakaway magnetic lanyard gets plugged into a USB port, and the other end of the lanyard gets attached to your person. If you get separated from your machine, the dongle sends customizable commands to either lock the screen or, for the sufficiently paranoid, nuke the hard drive. The designs are all up on GitHub, so check it out and think about what else this could be useful for.

If you like the look of low-poly models but hate the work involved in making them, our friend and Hack Chat alumnus Andrew Sink came up with a solution: an online 3D low-poly generator. The tool is pretty neat; it uses three.js and runs completely in-browser. All you have to do is upload an STL file and set sliders to get rid of as many triangles as you want. Great stuff, and fun to play with even if you don’t need to decimate your polygons.

And finally, what have you done with your oscilloscope for the last three years? Most of us can’t answer that except in the vaguest of terms, but then there’s DrTune, who took three years’ worth of screencaps from this Rigol DS1054z and strung them together into a 60-second movie. He swears he didn’t purposely sync the video to the soundtrack, which is “Flight of the Bumblebee” by Rimsky-Korsakov, but in some places it’s just perfect. See if you can guess what DrTune has been working on by watching the waveforms fly by. And watch for Easter eggs.

For years [Edward] has been building professional grade underwater sensing nodes at prices approachable for an interested individual without a government grant. An important component of these is temperature, and he has been on a quest to get the highest accuracy temperature readings from whatever parts hit that sweet optimum between cost and complexity. First there were traditional temperature sensor ICs, but after deploying numerous nodes [Edward] was running into the limit of their accuracy. Could he use clever code and circuitry to get better results? The short answer is yes, but the long answer is a many part series of posts starting in 2016 detailing [Edward]’s exploration to get there.

The first step is a thermistor, a conceptually simple device: resistance varies with temperature (seriously, how much more simple can a sensor get?). You can measure them by tapping the center of a voltage divider the same way you’d measure any other resistance, but [Edward] had discarded this idea because the naive approach combined with his Arduino’s 10 bit ADC yielded resolution too poor to be worthwhile for his needs. But by using the right analog reference voltage and adjusting the voltage divider he could get a 20x improvement in resolution, down to 0.05°C in the relevant temperature range. This and more is the subject of the first post.

What comes next? Oversampling. Apparently fueled by a project featured on Hackaday back in 2015 [Edward] embarked on a journey to applying it to his thermistor problem. To quote [Edward] directly, to get “n extra bits of resolution, you need to read the ADC four to the power of n times”. Three bits gives about an order of magnitude better resolution. This effectively lets you resolve signals smaller than a single sample but only if there is some jitter in the signal you’re measuring. Reading the same analog line with no perturbation gives no benefit. The rest of the post deals with the process of artificially perturbing the signal, which turns out to be significantly complex, but the result is roughly 16 bit accuracy from a 10 bit ADC!

What’s the upside? High quality sensor readings from a few passives and a cheap Arduino. If that’s your jam check out this excellent series when designing your next sensing project!