Haunted TV Does Mirror Scares With Raspberry Pi

November 13, 2020 by Lewin Day No comments

Hallowe’en may be over for another year, but that just means you’ve got more time to prepare your build for next time. [gocivici] has a fun twist on the classic mirror scare that might be just up your alley.

The build starts with an old black and white TV, hooked up to a Raspberry Pi 3. The Pi films the scene in front of the television through a camera secreted into the screen’s headphone jack, and displays it on screen. The camera feed is run through OpenCV, which runs face and eye detection algorithms to determine when a person is looking at the screen. Based on a basic timer script, when a viewer has looked long enough, a ghostly apparition is displayed, lurking behind the viewer. When the user looks over their shoulder, the apparition quickly disappears, as per the classical horror trope.

It’s a fun build that would make an excellent set piece for your next Hallowe’en party. For extra effect, be sure to secret it down a dark hallway with some IR LEDs illuminating the scene for the camera only. If you prefer something with a little more whimsy, consider these animated singing pumpkins instead. Video after the break.

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Wireless Earphones And Getting Them Back After They Fall On Tram Tracks

November 13, 2020 by Maya Posch 34 Comments

Over the past years, the trend has become to ditch anything with wires. This has led to many people dropping wired earphones and headphones for wireless (Bluetooth) versions. Yet along with the freedom from having the wires snagged on something and having earphones painfully torn out of your ears comes the very real risk of having them drop out of your ears to land potentially very inconvenient.

In Japan this has led to a big issue for railway companies, where throngs of commuters will often accidentally drop possessions onto the tracks. Staff members will then use a mechanical claw (‘magic hand’) to fetch them without having to risk their life by jumping down. With small items such as wireless earphones, this is however not so easy. With 947 cases of dropped earphones in the period of July-September in just the Tokyo area, this has led to desperate staff members coming up with new methods of easily retrieving the small gadgets.

Solutions range from putting something sticky like tape at the end of a stick, to modifying vacuum cleaners. Most recently Tokyo railway company JR East has collaborated with Panasonic to develop a vacuum cleaner-like device that is especially designed to easily retrieve such small items from the tracks, according to the Japan Times article.

The embedded video (also found after the break) from a Japanese broadcaster describes the issue in detail, along with tips on how to properly wear earphones so that they’re far less likely to fall out when you’re waiting on the tram or walking down the street. While it’s possible to fetch your dropped wireless earphones from the tracks, having someone step on it right after it falls out of your ear on the street is less easy to recover from.

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Robotics Club Teaches Soldering

November 13, 2020 by Al Williams 25 Comments

Oregon State University must be a pretty good place to go to school if you want to hack on robots. Their robotics club, which looks active and impressive, has a multi-part video series on how to solder surface mount components that is worth watching. [Anthony] is the team lead for their Mars Rover team and he does the job with some pretty standard-looking tools.

The soldering station in use is a sub-$100 Aoyue with both a regular iron and hot air. There’s also a cheap USB microscope that looks like it has a screen, but is covered in blue tape to hold it to an optical microscope. So no exotic tools that you’d need a university affiliation to match.

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“Artificial Sun” Lighting Via Old Satellite Dishes

November 13, 2020 by Lewin Day 53 Comments

Real sunlight is a beautiful thing, but due to the vagaries of Earth’s orbit and local weather systems, it’s not available all the time. [Matt] decided this wasn’t good enough, and set about building a rig to replicate the sun’s rays as closely as possible.

Rayleigh scattering is emulated by passing the light through a glass chamber filled with soapy water – taking advantage of the Tyndall effect.

The great distance between the Sun and the Earth means that the sun’s rays are essentially parallel from our local vantage point. Replicating this, and the soothing nature of a blue sky, were [Matt]’s primary goals with the project. To achieve this, an old satellite dish was pressed into service as a parabolic reflector, coated with mirror-finish vinyl strips. A 500W white LED with a good color rendering index was fitted at the focal point, outfitted with a water cooling system to shed heat. With a point source at its focal point, the parabolic reflector bounces the light such that it the rays are parallel, giving the sense that the light source is coming from an effectivelyl infinite distance away. To then achieve the blue sky effect, the light was then passed through a glass chamber filled with soapy water, which scatters the light using the Tyndall effect. This mimics the Rayleigh scattering in Earth’s atmosphere.

The final result is amazing, with [Matt] shooting footage that appears to be filmed in genuine daylight – despite being shot at night or on rainy days. He also features a cutdown build that can be achieved in a far cheaper and compact form, using Fresnel lenses and blue film. We’ve featured [Matt]’s daylight experiments before, though we’re amazed at the new level reached. Video after the break.

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Fran Finds Four Foot Alphanumeric Displays From 1910

November 13, 2020 by Chris Lott 19 Comments

Video blogger and display technology guru [Fran Blanche] has discovered a splendid retro-tech alphanumeric display from 1910. (Video, embedded below.)

We have always enjoyed her forays into old and unusual displays, including her project researching and reverse engineering an Apollo DSKY unit. This time [Fran] has dug up an amazing billboard from the early 20th century. It was built by the Rice Electric Display Company of Dayton Ohio, and operated in Herald Square for about two years. Requiring $400,000 in 1910-US-dollars to build, this was clearly an Herculean effort for its day and no doubt is the first example of selling advertising time on a computer-controller billboard. It boasts characters that are about 1.3 m tall and 1 m wide which can display letters, numbers, and various punctuation and symbols. These are arrayed into a 3-line 18-character matrix that is about 27 x 4 meters, and that’s up only a third of the total billboard, itself an illuminated and dynamic work of art.

Diagram Depicting the 3×18 Character Display

There are quite a few tantalizing details in the video, but a few that jumped out at us are the 20,000 light bulbs, the 40 Hz display update rate, the 150 km of wire used and the three month long installation time. We would really like to learn more about these two 7.5 kW motorized switch controllers, how were they programmed, how were the character segments arranged, what were their shapes?

In the video, you can see triangles arranged in some pattern not unlike more modern sixteen segment displays, although as [Fran] points out, Mr Rice’s characters are more pleasing. We hope [Fran] can tease out more details for a future video. If you have any ideas or knowledge about this display, please put them in the comments section below. Spoiler alert after the video…

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DSP Spreadsheet: The Goertzel Algorithm Is Fourier’s Simpler Cousin

November 13, 2020 by Al Williams 30 Comments

You probably have at least a nodding familiarity with the Fourier transform, a mathematical process for transforming a time-domain signal into a frequency domain signal. In particular, for computers, we don’t really have a nice equation so we use the discrete version of the transform which takes a series of measurements at regular intervals. If you need to understand the entire frequency spectrum of a signal or you want to filter portions of the signal, this is definitely the tool for the job. However, sometimes it is more than you need.

For example, consider tuning a guitar string. You only need to know if one frequency is present or if it isn’t. If you are decoding TouchTones, you only need to know if two of eight frequencies are present. You don’t care about anything else.

A Fourier transform can do either of those jobs. But if you go that route you are going to do a lot of math to compute things you don’t care about just so you can pick out the one or two pieces you do care about. That’s the idea behind the Goertzel. It is essentially a fast Fourier transform algorithm stripped down to compute just one frequency band of interest. The math is much easier and you can usually implement it faster and smaller than a full transform, even on small CPUs.

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Hackaday Podcast 093: Hot And Fast Raspberry Pi, Dr. Seuss Drone, M&M Mass Meter, And FPGA Tape Backup

November 13, 2020 by Mike Szczys No comments

Hackaday editors Mike Szczys and Elliot Williams wrangle the epic hacks that crossed our screens this week. Elliot ran deep on overclocking all three flavors of the Raspberry Pi 4 this week and discovered that heat sinks rule the day. Mike exposes his deep love of candy-coated chocolates while drooling over a machine that can detect when the legume is missing from a peanut M&M. Core memory is so much more fun when LEDs come to play, one tiny wheel is the power-saving secret for a very strange multirotor drone, and there’s more value in audio cassette data transfer than you might think — let this FPGA show you how it’s done.

Take a look at the links below if you want to follow along, and as always, tell us what you think about this episode in the comments!

Direct download (~70 MB)