Homebrewed Voice Assistant Keeps An Eye On Air Quality

November 5, 2021 by Lewin Day 3 Comments

Voice assistants are now available from a wide variety of companies, however, [7402] didn’t like the idea of these devices sending data off to the cloud for potentially-nefarious purposes. Thus, the goal became to build a home voice assistant that worked entirely offline, and that’s precisely what [7402] achieved.

The system had limited goals compared to commercial competitors. [7402] was more than happy to deal with a limited vocabulary of understanding as a trade off for privacy. It’s all built around a Raspberry Pi Zero, which runs the Julius speech recognition library. Ultrasonic sensors are used to only activate the device when a person leans in and directly addresses the system.

Capabilities include reporting on the weather, switching light on and off, and advising users of air quality readings from the local authorities. Feedback to the user is via text-to-speech as well as flashing LEDs. The latter are used to create a quirky, retro “thinking” animation to indicate the system is processing, and has indeed heard a spoken command.

It’s a neat build, and one that covers most of the good things that commercial cloud devices are capable of anyway. As a bonus, no smartphone apps are required, nor will private companies impact the system’s functionality as it relies on no external servers to operate.

We’ve seen similar builds before too, such as this GlaDOS-themed voice assistant. Video after the break.

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Space Shuttle Model In A Hypersonic Wind Tunnel

Mach 20 In A Wind Tunnel: Yes, It’s Rocket Science

November 4, 2021 by Ryan Flowers 5 Comments

Hypersonic speeds are defined by those exceeding Mach 5, and lately there’s been a lot of buzz about unmanned hypersonic vehicles making test flights. Vehicles returning from orbital flight also travel at hypersonic speeds as they do their best to transition back to the terrestrial realm. Before anything leaves ground though, these machines are tested in wind tunnels. [Scott Manley]’s video “How Hypersonic Wind Tunnels Recreate Mach 20” (embedded below) does a wonderful job of explaining the engineering behind wind tunnels for testing hypersonic vehicles.

While the earliest wind tunnels such as that used by the Wright Brothers were powered by simple fans, it is not possible for any propeller to surpass subsonic speeds. This is evidenced by there not being any propeller driven aircraft that can exceed Mach 1. Since an aircraft can’t reach those speeds with a propeller, it follows that a wind tunnel cannot be driven by propellers, fans, or any such device, and exceed Mach 1 wind speed, either. So it begs the question: Just how do they do it?

You might think that the answer lays in Bernoulli’s law – but it does not. You might think it involves compressing the air into smaller and smaller tubes and pipes. It doesn’t. As [Scott Manley] so expertly explains in the video below the break, it has quite a lot in common with actual rocket science.

You may be interested to know that we’ve covered some DIY wind tunnel builds as well as a small desktop wind tunnel in the past. While not hypersonic, they’re exactly what you’d want to have if you’re an aerospace hacker of any kind.

Thanks [Zane Atkins] for the tip!

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Hedgehog Gesture Sensor Built With Cheap Time-of-Flight Modules

November 2, 2021 by Lewin Day 6 Comments

Time-of-flight sensors used to be expensive obscurities, capable of measuring the travel time of photons themselves and often used for tracking purposes. However, the technology is cheaper now, such that [jean.perardel] has used TOF sensors to build a useful and affordable gesture-tracking system.

The system relies on four VL53L1X time of flight sensors, which have a 16×16 scanning array and communicate over the I2C bus. Controlling the show is an Arduino MKR1010, though the project should be achievable with a range of other microcontrollers, too.

The device is built into a cute hedgehog-like form factor, with an LCD screen acting as the face. It displays facial expressions which show how the system is interpreting and responding to gestures. It gives the project lots of personality, which makes using the system more fun. Gestures from the system can be used to send keystrokes over USB, control relays or servos, or even fire IR signals to control TVs and other hardware.

It actually seems like a useful gesture control interface, one that could become a useful part of a workstation setup. We’ve seen gesture controls put to other uses too, like controlling robot arms. Video after the break.

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Building A Bicycle Dash Cam With Advanced Capabilites

November 1, 2021 by Lewin Day 15 Comments

Riding a bicycle is a wonderful and healthy way to get around. However, just like with any other vehicle on the road, it can be useful to have a camera to record what goes on in traffic. [Richard Audette] built just such a rig.

The original setup relies on a Raspberry Pi 3, which takes a photo every 10 seconds using the attached Pi Camera. It then processes these photos using OpenALPR, which is a piece of software for reading licence plates. Licence plates detected while cycling can be stored on the Raspberry Pi for later, something which could be useful in the event of an accident.

However, [Richard] has developed the concept further since then. The revised dashcam adds blind spot detection for added safety, and uses a Luxonis OAK-D camera which provides stereo depth data and has AI acceleration onboard. It’s paired with a laptop carried in a backpack instead of a Raspberry Pi, and can stream video to a smartphone sitting on the handlebars as a sort of rear-view mirror.

Anyone who has commuted on a bicycle will instantly see the value in work like [Richard]’s. Just avoiding one accident from a car coming from behind would be of huge value, and we’re almost surprised we don’t see more bicycle rear view kits in the wild.

Alternatively, if you just want to scan your surroundings as you ride, consider building a landscape scanner instead. Video after the break.

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Smoothing Out Foam Parts With Lots Of Gesso

November 1, 2021 by Tom Nardi 16 Comments

Whether you’re building a product mock-up or a lightweight enclosure, carving your parts out of hard foam is a fast way to get the job done. Unfortunately, the end result can have a bit of a rough finish; a problem if you’re looking to attract investors or get some nice shots so you can send your handiwork into Hackaday.

If you ever find yourself in a situation where you need to make a carved piece of foam look like it isn’t a carved piece of foam, this tip from prolific maker [Eric Strebel] could really come in handy. Rather than using some spray-on primer or epoxy coating, things that can be difficult to work with when you’re confined to a small home workspace, he recommends sealing it up with several coats of gesso.

The gesso fills in the tiny voids in the foam’s surface.

For the less artistically inclined in the audience, gesso is essentially a paint that’s been combined with chalk or gypsum to make it thicker. Gesso is generally used to prepare an absorbent surface (such as wood or canvas) before applying paint. In this case, [Eric] is using it to build up the surface of the foam and seal up all the open pores.

The downside is that the gesso requires several coats to really build up. [Eric] puts six coats on in this demonstration before he starts to thin it out a bit with water. At that point, each successive coat is sanded with increasingly higher grits. After nine coats, he does his finish sanding with 600 grit paper, and the results look fantastic.

To add some color [Eric] dyed the piece and then used a toothbrush to flick on some black and white paint, creating a very convincing granite-like finish. Unfortunately, his attempt to brush on a water-based sealer caused this finish to run, and he had to take it all off. In the end, he had to resort to using spray paint to finish the piece, but at least it was a simple rattle can.

This isn’t the first time [Eric] has experimented with alternative priming techniques. He’s a big fan of two-component primer in a can, which lets you lay down a professional finish without the expense and complication of using a spray gun.

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A Builders Guide For The Perfect Solid-State Tesla Coil

October 31, 2021 by Dave Rowntree 14 Comments

[Zach Armstrong] presents for your viewing pleasure a simple guide to building a solid-state Tesla coil. The design is based around a self-resonant setup using the UCC2742x gate driver IC, which is used in a transformer-coupled full-wave configuration for delivering maximum power from the line input. The self-resonant bit is implemented by using a small antenna nearby the coil to pick up the EM field, and by suitably clamping and squaring it up, it is fed back into the gate driver to close the feedback loop. Such a setup within reason allows the circuit to oscillate with a wide range of Tesla coil designs, and track any small changes, minimizing the need for fiddly manual tuning that is the usual path you follow building these things.

Since the primary is driven with IGBTs, bigger is better. If the coil is too small, the resonant frequency would surpass the recommended 400 kHz, which could damage the IGBTs since they can’t switch much faster with the relatively large currents needed. An important part of designing Tesla coil driver circuits is matching the primary coil to the driver. You could do worse than checkout JavaTC to help with the calculations, as this is an area of the design where mistakes often result in destructive failure. The secondary coil design is simpler, where a little experimentation is needed to get the appropriate degree of coil coupling. Too much coupling is unhelpful, as you’ll just get breakdown between the two sides. Too little coupling and efficiency is compromised. This is why you often see a Tesla coil with a sizeable gap between the primary and secondary coils. There is a science to this magic!

A 555 timer wired to produce adjustable pulses feeds into the driver enable to allow easily changing the discharge properties. This enables it to produce discharges that look a bit like a Van De Graaff discharge at one extreme, and produce some lovely plasma ‘fire’ at the other.

We’ve covered Tesla coils from many angles over the years, recently this plasma tweeter made sweet sounds, and somehow we missed an insanely dangerous Tesla build by [StyroPyro] just checkout that rotary spark gap – from a distance.

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EMC Tutorial Puts You In The Loop

October 29, 2021 by Al Williams 2 Comments

A student once asked his lab instructor why his amplifier was oscillating. After looking at it and noting the wild construction, the instructor remarked, “A better question would be why shouldn’t it oscillate?” The truth of it is, our circuits generate noise and especially if they are oscillating anyway. Distortion and nonlinearities generate harmonics and other component imperfections also contribute.

[FesZ Electronics] has a great video series about noise in switching power supplies and the latest talks about the hot loop. If you want to improve the noise performance of your next design, these videos are well worth watching. You can see the hot loop video below.

We really liked the homebrew noise probes. In addition to real-world probing. The video also observes circuit operation under simulation. Even if you don’t care about noise performance, there’s a lot of good information about basic switching power supply design here.

You can see the difference in a PCB that has a small hot loop versus a very small hot loop. Something to think about next time you are laying out a power supply board.

If you want to dive deeper into noise simulation, we have a good read on that for you. Or ditch simulation, and make your own cheap probe with an SDR dongle.

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