High-Tech Paperweight Shows Off Working 60s-era Thin-Film Electronics

July 12, 2021 by Donald Papp 9 Comments

[Ken Shirriff]’s analysis of a fascinating high-tech paperweight created by GE at the height of the space race is as informative as it is fun to look at. This device was created to show off GE’s thin-film electronics technology, and while it’s attractive enough on its own, there’s an added feature: as soon as the paperweight is picked up, it begins emitting a satellite-like rhythmic beep. It is very well-made, and was doubtlessly an impressive novelty for its time. As usual, [Ken] dives into what exactly makes it tick, and shares important history along the way.

Thin-film module with labels, thanks to [Ken]’s vintage electronics detective work. Click to enlarge.

In the clear area of the paperweight is a thin-film circuit, accompanied by a model of an early satellite. The module implements a flip-flop, and the flat conductors connect it to some additional components inside the compartment on the left, which contains a power supply and the necessary parts to create the beeps when it is picked up.

Thin-film electronics reduced the need for individual components by depositing material onto a substrate to form things like resistors and capacitors. The resulting weight and space savings could be considerable, and close-ups of the thin film module sure look like a precursor to integrated circuits. The inside of the left compartment contains a tilt switch, a battery, a vintage earphone acting as a small speaker, and a small block of components connected to the thin-film module. This block contains two oscillators made with unijunction transistors (UJTs); one to create the beep, and one to control each beep’s duration. The construction and overall design of the device is easily recognizable, although some of the parts are now obsolete.

If you’d like a bit more detail on exactly how this device worked, including circuit diagrams and historical context, be sure to click that first link, and pay attention to the notes and references at the end. One other thing that’s clear is that functional electronics embedded in clear plastic shapes simply never go out of style.

Skin-Mounted Wearable Bend Sensor Gets Close And Personal

July 10, 2021 by Donald Papp 1 Comment

[Mikst] has been working on wearable electronics and sensors for a long time, and shared the results of a different kind of bend sensor that fits directly onto the skin. It’s true that this kind of sensor design isn’t re-usable, but it is also very simple and inexpensive. It’s just a proof of concept right now, but we could see it or some of the other ideas [Mikst] tries, used in niche wearable applications where space is critical, like cosplay.

At its heart the sensor is made from two strands of conductive thread and a small strip of stretchy, conductive fabric common in wearable e-textiles. It is stuck directly to the skin using a transparent, non-woven medical adhesive dressing that is particularly good at conforming to contoured areas of the body. In this case, it is used to stick the stretchy piece of conductive fabric directly onto [Mikst]’s knuckle, where it responds to even small movements. You can watch a multimeter measuring the resistance changes in the video, embedded below.

We’ve seen [Mikst]’s work before in finding unusual solutions to e-textile problems, such as a three-conductor pivoting connection used to mount a wearable hall effect sensor.

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USB Power Bank’s Auto-Off Becomes Useful Feature In Garage Door Remote

July 6, 2021 by Donald Papp 10 Comments

For devices that are destined for momentary and infrequent use as well as battery power, some kind of power saving is pretty much a required feature. For example, when [PJ Allen] turned two ESP8266-based NodeMCU development boards into a replacement wireless remote garage door opener, a handy USB power bank ended up serving as a bit of a cheat when migrating the remote away from the workbench. Instead of moving the board from USB to battery power and implementing some kind of sleep mode or auto-off, [PJ Allen] simply plugged in a USB power bank and let it do all the work.

This is how the feature works: some USB power banks turn themselves off unless they detect a meaningful current draw. That means that if the power bank is charging a phone, it stays on, but if it’s only lighting up a few LEDs, it’ll turn itself off. This feature can be a frustrating one, but [PJ Allen] realized that it could actually be useful for a device like his garage door remote. Turning on the power bank delivers 5 V to the NodeMCU board and allows it to work, but after about fifteen seconds, the power bank turns itself off. Sure, strapping a power bank to the remote makes the whole thing bigger than it needs to be, but it’s a pretty clever use of the minimum load as an effortless auto-off feature.

The NodeMCU boards in [PJ Allen]’s DIY remote use ESP-NOW for their wireless communications, a nifty connectionless protocol from Espressif that we’ve seen used in other projects as well, such as this ESP32-based walkie-talkie.

A New Spin On Empty Filament Spools For Part Storage

July 5, 2021 by Donald Papp 26 Comments

Empty spools from 3D printer filament are the kind of thing that begs to be repurposed, and one option is [3d-printy]’s vertical filament spool parts drawer design. The way this solution works is by using the spool to hold twelve vaguely pie-shaped drawers that can be individually unlocked and removed entirely, which makes accessing their contents (or dumping them out) much easier. This method requires the spools to be oriented vertically, so it ends up handling a bit like a Rolodex.

One downside of the design is that it requires two inserts to be installed on the inside of the spool walls, which act as guide rails and lock points for the drawers. Another is that managing a vertical spool can be a bit awkward, given its lack of flat surfaces. Happily, there is an option for a matching stand that not only provides a flat base, but keeps any accidentally-unlocked drawers from falling out and spilling their contents.

The project files are OpenSCAD files, which allows easy customization for different spool manufacturers and dimensions, and [3d-printy] provides measurements for some common ones. Another nice element of this design is that no single part uses more than 30 grams of filament, which makes printing them an attractive way to use up the last bits of filament rolls.

We’ve seen drawer-style storage for filament spools before, but haven’t seen a design quite like this one before. Watch an overview of the drawer design as well as the spool holders in the videos, embedded below.

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Hacking A Thermal Imager For Dual-use Of The Thermal Sensor

July 4, 2021 by Donald Papp 3 Comments

Sometimes a device doesn’t do quite what one needs, and in those cases a bit of tampering might do the trick. That’s what led to being able to record video from a HTI HT-A1 thermal imager despite the device not actually supporting that function, thanks to careful investigation and warranty violation.

Plugging in a custom USB cable allows a mobile phone app to access the thermal sensor, while the host device itself remains ignorant.

We’ve seen a teardown of the HT-A1 in the past, and it turns out that Seek — the manufacturer for the actual thermal sensor inside the device — released an OEM development kit and mobile phone app for their modules. Could this mean that the raw sensor module in the HT-A1 could be accessed via the developer kit app? One hacked together USB cable later showed that the answer is yes! Not only does the app allow viewing thermal imagery, but it makes it possible to do things like record video (a function the HT-A1 itself does not support.)

But even if the HT-A1 doesn’t allow recording, as a handheld thermal sensor with a screen it’s still pretty useful in its own way and it would be shame to gut the unit just for a raw sensor module. The best solution ended up being to put the sensor back into the HT-A1, and install some switching circuitry to disconnect the sensor from the HT-A1’s CPU and divert its data to the USB plug on demand. This means the HT-A1 can be used normally, but by plugging in a custom-made cable while the unit is off, the thermal sensor can be accessed by the mobile phone app instead. Best of both worlds. You can see a brief celebratory thermal cat video embedded below, proving it works.

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Robotic Ball-Bouncing Platform Learns New Tricks

June 30, 2021 by Donald Papp 11 Comments

[T-Kuhn]’s Octo-Bouncer platform has learned some new tricks since we saw it last. If you haven’t seen it before, this device uses computer vision from a camera mounted underneath its thick, clear acrylic platform to track a ball in 3D space, and make the necessary (and minute) adjustments needed to control the ball’s movements with a robotic platform in real time.

We loved the Octo-Bouncer’s mesmerizing action when we saw it last, and it’s only gotten better. Not only is there a whole new custom ball detection algorithm that [T-Kuhn] explains in detail, there are also now visualizations of both the ball’s position as well as the plate movements. There’s still one small mystery, however. Every now and again, [T-Kuhn] says that the ball will bounce in an unexpected direction. It doesn’t seem to be a bug related to the platform itself, but [T-Kuhn] has a suspicion. Since contact between the ball and platform is where all the control comes from, and the ball and platform touch only very little during a bounce, it’s possible that bits of dust (or perhaps even tiny imperfections on the ball’s surface itself) might be to blame. Regardless, it doesn’t detract from the device’s mesmerizing performance.

Design files and source code are available on the project’s GitHub repository for those who’d like a closer look. It’s pretty trippy watching the demonstration video because there is so much going on at once; you can check it out just below the page break.

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Just How Did 1500 Bytes Become The MTU Of The Internet?

June 29, 2021 by Donald Papp 59 Comments

[Benjojo] got interested in where the magic number of 1,500 bytes came from, and shared some background on just how and why it seems to have come to be. In a nutshell, the maximum transmission unit (MTU) limits the maximum amount of data that can be transmitted in a single network-layer transaction, but 1,500 is kind of a strange number in binary. For the average Internet user, this under the hood stuff doesn’t really affect one’s ability to send data, but it has an impact from a network management point of view. Just where did this number come from, and why does it matter?

[Benjojo] looks at a year’s worth of data from a major Internet traffic exchange and shows, with the help of several graphs, that being stuck with a 1,500 byte MTU upper limit has real impact on modern network efficiency and bandwidth usage, because bandwidth spent on packet headers adds up rapidly when roughly 20% of all packets are topping out the 1,500 byte limit. Naturally, solutions exist to improve this situation, but elegant and effective solutions to the Internet’s legacy problems tend to require instant buy-in and cooperation from everyone at once, meaning they end up going in the general direction of nowhere.

So where did 1,500 bytes come from? It appears that it is a legacy value originally derived from a combination of hardware limits and a need to choose a value that would play well on shared network segments, without causing too much transmission latency when busy and not bringing too much header overhead. But the picture is not entirely complete, and [Benjojo] asks that if you have any additional knowledge or insight about the 1,500 bytes decision, please share it because manuals, mailing list archives, and other context from that time is either disappearing fast or already entirely gone.

Knowledge fading from record and memory is absolutely a thing that happens, but occasionally things get saved instead of vanishing into the shadows. That’s how we got IGNITION! An Informal History of Liquid Rocket Propellants, which contains knowledge and history that would otherwise have simply disappeared.