A Bend Sensor Developed With 3D Printer Filament

April 13, 2024 by Jenny List 6 Comments

PhD students spend their time pursuing whatever general paths their supervisor has given them, and if they are lucky, it yields enough solid data to finally write a thesis without tearing their hair out. Sometimes along the way they result in discoveries with immediate application outside academia, and so it was for [Paul Bupe Jr.], whose work resulted in a rather elegant and simple bend sensor.

The original research came when shining light along flexible media, including a piece of transparent 3D printer filament. He noticed that when the filament was bent at a point that it was covered by a piece of electrical tape there was a reduction in transmission, and from this he was able to repeat the effect with a piece of pipe over a narrow air gap in the medium.

Putting these at regular intervals and measuring the transmission for light sent along it, he could then detect a bend. Take three filaments with the air-gap-pipe sensors spaced to form a Gray code, and he could digitally read the location.

He appears to be developing this discovery into a product. We’re not sure which is likely to be more stress, writing up his thesis, or surviving a small start-up, so we wish him luck.

Rabbit Sighted In The Wild

April 13, 2024 by Jenny List 21 Comments

Here at Hackaday we’re suckers for old abandoned technologies, the more obscure the better. The history of the telephone has plenty to capture our attention, and it’s from that arena that something recently floated past our timeline. [IanVisits] reports a sighting of a Rabbit in a London Underground station. The bunny in question definitely isn’t hopping though, it’s been dead for more than three decades. It’s a base station for a failed digital mobile phone system.

We’ve had a look in the past at CT2, the system this Rabbit base station once formed part of. It was an attempt to make an inexpensive phone system by having the handsets work with fixed base stations rather than move from cell to cell. It was one of the first public digital mobile phone systems, but the convenience of a phone that could both receive calls and make them anywhere without having to find a base station meant that GSM phones took their market.

The one in Seven Sisters tube station is a bit grubby looking, but it’s not the only survivor out there in the field. We have to admit to being curious as to whether it’s still powered on even though its backhaul will be disconnected, as in our experience it’s not uncommon for old infrastructure to be left plugged into the wall for decades, unheeded. Does anyone fancy sniffing for it with a Flipper Zero?

Do You Trust Your Cheap Fuses?

April 11, 2024 by Jenny List 34 Comments

When a fuse is fitted in a power rail, it gives the peace of mind that the circuit is protected. But in the case of some cheap unbranded fuses of the type that come in kits from the usual online suppliers that trust can be illusory, as they fail to meet the required specification.

[Andreas Spiess] has used just these fuses for protection for years as no doubt have many of you, so it was something of a shock for him to discover that sometimes they don’t make the grade. He’s taken a look at the issue for himself, and come up with an accessible way to test your fuses if you have any of those cheap ones.

It’s an interesting journey into the way fuses work, as we’re reminded that the value written on the fuse isn’t the current at which it blows but the maximum it’s intended to take. The specification for fuses should have a graph showing how quickly one should blow at what currents above that level, and the worry was that this time would be simply too long for the cheap ones.

In the video below the break, he looks at the various set-ups required to test a fuse, and instead of a bank of large power supplies, he came up with a circuit involving an 18650 cell and three one ohm resistors in parallel. The resulting 1/3 ohm resistor should pass in the region of 10 A when connected across the 18650, so with a 5 A fuse in that circuit and a storage ‘scope he’s able to quickly test a few candidates. He found that the cheap fuses he had were slower to blow than a Bosch part but weren’t as worrisome as he’d at first thought. If you have any of these parts, maybe you should take a look at them too?

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Bye Bye Green Screen, Hello Monochromatic Screen

April 9, 2024 by Jenny List 58 Comments

It’s not uncommon in 2024 to have some form of green background cloth for easy background effects when in a Zoom call or similar. This is a technology TV and film studios have used for decades, and it’s responsible for many of the visual effects we see every day on our screens. But it’s not perfect — its use precludes wearing anything green, and it’s very bad at anything transparent.

The 1960s Disney film makers seemingly had no problem with this as anyone who has seen Mary Poppins will tell you, so how did they manage to overlay actors with diaphanous accessories over animation? The answer lies in an innovative process which has largely faded from view, and [Corridor Crew] have rebuilt it.

Green screens, or chroma key, to give the effect its real name, relies on the background using a colour not present in the main subject of the shot. This can then be detected electronically or in software, and a switch made between shot and inserted background. It’s good at picking out clean edges between green background and subject, but poor at transparency such as a veil or a bottle of water. The Disney effect instead used a background illuminated with monochromatic sodium light behind the subject illuminated with white light, allowing both a background and foreground image to be filmed using two cameras and a dichroic beam splitter. The background image with its black silhouette of the subject could then be used as a photographic stencil when overlaying a background image.

Sadly even Disney found it very difficult to make more than a few of the dichroic prisms, so the much cheaper green screen won the day. But in the video below the break they manage to replicate it with a standard beam splitter and a pair of filters, successfully filming a colourful clown wearing a veil, and one of them waving their hair around while drinking a bottle of water. It may not find its way back into blockbuster films just yet, but it’s definitely impressive to see in action.

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A Spark Gap Transmitter, Characterized

April 7, 2024 by Jenny List 32 Comments

When we think of a spark gap radio transmitter, most of us immediately imagine an early twentieth century ship’s radio room or similar. Most of us know these transmitters as the first radio systems, and from there we’ll probably also know that they were phased out when better circuits arrived, because of their wide bandwidth. So it’s rare in 2024 to find anyone characterizing a spark gap transmitter, as [Baltic Lab] has.

The circuit is simple enough, a high voltage passes through an RC network to a spark gap, the other side of which is a tuned circuit. The RC network and the spark gap form a simple low frequency relaxation oscillator, with the C being charged until the spark gap triggers, forcing the subsequent discharge of the capacitor and causing the spark to extinguish and the cycle to repeat. The resulting chain of high voltage pulses repeatedly energizes the tuned circuit, with each pulse causing a damped oscillation at its resonant frequency. The resulting RF signal is a crude AM tone which can be received fairly simply.

The mathematics behind it all is pretty interesting, revealing both the cause of the bandwidth spread in the low Q factor of the tuned circuit, and the presence of a large spurious frequency spike on an interaction with the capacitor in the RC circuit. It’s all in the video below the break, and we have to admit, it taught us something about radio we didn’t know.

Meanwhile spark gaps weren’t the only early radio transmitter technology. How about an alternator?

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Emergency DIP Pin Repair For Anyone

April 7, 2024 by Jenny List 20 Comments

Who has not at some point in their lives experienced the horror of a pin on a DIP package breaking off? It’s generally game over, but what if you don’t have another chip handy to substitute? It’s time to carefully grind away some of the epoxy and solder on a new pin, as [Zafer Yildiz] has done in the video below the break.

The technique relies on the pins continuing horizontally inside the package , such that they provide a flat surface. He’s grinding with the disk on a rotary tool, we have to say we’d use one of the more delicate grinding heads for something more akin to a miniature die grinder.

Once the flat metal surface is exposed, the chip is placed in a socket, and a new pin is cut from the leg of a TO-220 power device. This is carefully bent over, inserted in the socket, and soldered into place. The whole socket and chip arrangement is then used in place of the chip, making for something a little bulky but one infinitely preferable to having to junk the device.

There are many useful skills to be learned when it comes to reworking, and we’ve covered a few in our time. Most recently we saw a guide to lifting SMD pins.

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The Easy Way To Make A Smart Appliance

April 7, 2024 by Jenny List 32 Comments

It seems that finding an appliance without some WiFi connectivity and an app to load your laundry data into the cloud is an increasingly difficult thing to do in the 2020s. Many of us resolutely refuse to connect these smart appliances to the Internet, but not because we don’t see the appeal — we just want to do it on our own terms.

[Terence Eden] did just this with his rice cooker, using a surprisingly straightforward approach. He simply connected it to the mains via an energy monitoring smart plug, and that was the hardware part, done. Of course, were it that simple we probably wouldn’t be featuring this here, as the meat of this project lies in connecting it to his smart home systems and getting something useful from it.

He’s using Home Assistant, and after a bit of messing about had it part of his home automation system. Then it was time for Appliance Status Monitor, which allowed him to easily have the rice cooker send him a notification once it has done its thing by monitoring the power it was using. All online, part of a smart home, and not a byte of his data captured and sold to anyone!

This isn’t the first home automation project we’ve brought you from this source.