Pulling A Crystal By Grinding It

May 10, 2020 by Jenny List 29 Comments

If you own a radio transmitter, from a $10 Baofeng handheld to a $1000 fancy all-band transceiver, setting the frequency is simply a case of dialing in where you want to go. A phase-locked-loop frequency synthesizer or a software-defined radio will generate your frequency, and away you go. There was a time though when synthesizers were impossibly complex and radio amateurs were faced with a simple choice. Use an LC oscillator and put up with drifting in frequency, or use a crystal oscillator, and be restricted to only the frequencies of the crystals you had. [Mark Erdle, AE2EA] modified a 1950s broadcast AM broadcast transmitter for the 1.8MHz amateur band, and his friend [Andy Flowers, K0SM] thought it needed its crystal back for originality rather than the external frequency source [Mark] had provided. He documents the process of modifying a crystal oven and moving a crystal frequency in the video below the break.

A crystal oven is a unit containing the crystal itself alongside a thermostatic heater, and in this one, the crystal was a 1970s-vintage hermetically sealed HC6 device. He modified the oven to take a socket for older FT243 crystals because the quartz element can easily be accessed. [Andy] picked a crystal as close as he could find below the required frequency. He then ground it down with very fine grit on a glass plate, reducing its mass and thus its resonant frequency. We’re taken through the process of getting it close to frequency, but sadly don’t see the etching that he uses for the very last stage. At the end of the video, we see a QSO on the transmitter itself, which is something of an oddity in an age when AM on amateur bands has been supplanted by other modes for decades.

If you’re curious about the transmitter there’s a video thread following its restoration, and if the guts of older radio gear interests you then take a look at this aircraft receiver lovingly brought back to life.

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Turn An Unused Pi Zero Into A Parts Bin WiFi Extender

May 10, 2020 by Tom Nardi 17 Comments

We know a lot of you are sitting on an unused Raspberry Pi Zero W, maybe even several of them. The things are just too small and cheap not to buy in bulk when the opportunity presents itself. Unfortunately, the Zero isn’t exactly a powerhouse, and it can sometimes be tricky to find an application that really fits the hardware.

Which is why this tip from [Tejas Lotlikar] is worth taking a look at. Using the Pi Zero W, a cheap USB WiFi adapter, and some software trickery, you can put together a cheap extender for your wireless network. The Pi should even have a few cycles left over to run ad-blocking software like Pi-hole while it shuffles your packets around the tubes.

[Tejas] explains every step of the process, from putting the Raspbian image onto an SD card to convincing wpa_supplicant to put the Pi’s WiFi radio into Access Point mode. Incidentally, this means that you don’t need to be very selective about the make and model of the USB wireless adapter. Something with an external antenna is preferable since it will be able to pull in the weak source signal, but you don’t have to worry about it supporting Soft AP.

With the software configured, all you need to finish this project off is an enclosure. A custom 3D printed case large enough to hold both the Pi and the external WiFi adapter would be a nice touch.

Reverse Engineering Saves Trashed LED Panels

May 9, 2020 by Tom Nardi 8 Comments

While out riding his bike, [Hammond Pearce] came across a dumpster overflowing with large LED panels. Despite the fact that the model numbers didn’t reveal anything helpful after some online searching, he decided to pedal off with as many as he could safely carry. The COVID-19 lockdown left him with only a limited set of tools, be he still managed to crack the protocol used to control his e-waste score and document it for our reading pleasure.

Between the helpful labels on the PCB silkscreen and the advice of a friend that used to work on digital road signs, it didn’t take [Hammond] long to get a general idea of what the panels were looking for in terms of power and control. Especially once he noticed the MBI5024 shift registers dotting the board.

The next step was to take an ATmega328PB based development board and start throwing data at the panel’s input lines to see if he could elicit a response. With careful attention and some custom code, he eventually figured out that each byte of data sent down the line would control a 4 x 2 section of LEDs.

Once he had the basics down, the next step was to start expanding his code to handle things like shapes, text, and daisy-chained panels. After posting some of his work to Reddit, cyber-sleuths determined that the protocol appeared to be some variation of HUB75, which gave [Hammond] hints on what some of the other pins in the connector might be used for. He’s released all of his code online for anyone who might find it useful, but since he still doesn’t know who made these panels and why there’s really no telling how many of them are actually floating around out there.

Figuring out how to talk to an unknown or undocumented piece of hardware can be intimidating, but success stories like these are reminders of why it’s worth putting the effort in. As we’ve seen, the difference between trash and treasure is often a keen eye and a few lines of code.

Nightmare Fuel Telepresence ‘Bot May Become Your Last Friend

May 9, 2020 by Kristina Panos 15 Comments

After this pandemic thing is all said and done, historians will look back on this period from many different perspectives. The one we’re most interested in of course will concern the creativity that flourished in the petri dish of anxiety, stress, and boredom that have come as unwanted side dishes to stay-at-home orders.

[Hunter Irving] and his brother were really missing their friends, so they held a very exclusive hackathon and built a terrifying telepresence robot that looks like a mash-up of Wilson from Castaway and that swirly-cheeked tricycle-riding thing from the Saw movies. Oh, and to make things even worse, it’s made of glow-in-the-dark PLA.

Now when they video chat with friends, TELEBOT is there to make it feel as though that person is in the room with them. The Arduino Uno behind its servo-manipulated vintage doll eyes uses the friend’s voice input to control the wind-up teeth based on their volume levels. As you might imagine, their friends had some uncanny valley issues with TELEBOT, so they printed a set of tiny hats that actually do kind of make it all better. Check out the build/demo video after the break if you think you can handle it.

Not creepy enough for you? Try building your own eyes from the ground up.

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Halloween Costume Turned Positive Pressure Suit

May 9, 2020 by Tom Nardi 31 Comments

As a general rule, you probably shouldn’t be getting your Personal Protective Equipment (PPE) from the party store. But these are exceptional times, and rather than potentially depriving medical professionals the equipment they so desperately need on the front lines, the team at [Robots Everywhere] has been looking into improvised PPE. We’re not sure things are at the point where you would need to don this DIY Positive Pressure Suit (PAPR), but it’s certainly an interesting look at what’s possible when you think outside the box.

At the most basic level, a PAPR is a mostly air-tight garment that is continuously pumped full of filtered air. As long as the pressure inside the suit is higher than outside, there’s no way airborne bacteria and viruses can get in without traveling through the filter first.

For this project, the folks at [Robots Everywhere] took an inflatable astronaut costume and replaced the dinky original air pump with a much larger 12 V unit designed for inflating air beds. Upgrading the pump not only increased the internal air pressure of the suit, but also made it easier to add a HEPA filter to the inlet. As long as the suit is inflated and there are no leaks in the hose, the wearer will be surrounded by a bubble of filtered air.

Presumably, you don’t want to be tethered to the wall though, so the write-up briefly touches on how the pump system can be made more mobile with the addition of an RC-style battery pack. With the pump and batteries secured in a pouch attached to the suit, the wearer is free to venture outside the confines of their self-isolation bunker and go about their dystopian daily business.

A getup like this might seem a bit excessive, but with so many folks desperate for information on homemade protective gear, we aren’t passing any judgment. The team says you can modify a cheap painter’s suit in much the same way, but frankly, that doesn’t sound nearly as fun to us.

[Thanks to Aron for the tip.]

Touch-Typing On Fingertips? Prototype Says It Could Work

May 9, 2020 by Donald Papp 11 Comments

The fingertips are covered in touch sensors, each intended to be tapped by the thumbtip of the same hand.

Touch-typing with thumbs on a mobile phone keyboard is a pretty familiar way to input text, and that is part of what led to BiTipText, a method of allowing bimanual text input using fingertips. The idea is to treat the first segments of the index fingers as halves of a tiny keyboard, whose small imaginary keys are tapped with the thumbs. The prototype shown here was created to see how well the concept could work.

The prototype hardware uses touch sensors that can detect tap position with a high degree of accuracy, but the software side is where the real magic happens. Instead of hardcoding a QWERTY layout and training people to use it, the team instead ran tests to understand users’ natural expectations of which keys should be on which finger, and how exactly they should be laid out. This data led to an optimized layout, and when combined with predictive features, test participants could achieve an average text entry speed of 23.4 words per minute.

Judging by the prototype hardware, it’s understandable if one thinks the idea of fingertip keyboards may be a bit ahead of its time. But considering the increasingly “always on, always with you” nature of personal technology, the goal of the project was more about investigating ways for users to provide input in fast and subtle ways. It seems that the idea has some merit in principle. The project’s paper can be viewed online, and the video demonstration is embedded below.

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An Op-Amp From The Ground Up

May 9, 2020 by Jenny List 18 Comments

We are all used to the op-amp, as a little black box from which we can derive an astonishingly useful range of circuit functions. But of course within it lurks a transistor circuit on a chip, and understanding the operation of that circuit can give us insights into the op-amp itself. It’s a subject [IMSAI Guy] has tackled during the lockdown, recording a set of videos explaining a simple discrete-component op-amp.

He starts with the current source, a simple circuit of two diodes, a resistor, and a transistor that sets the bias for the two-transistor differential amplifier. This is followed by a look at the output driver, and we would expect that shortly to come will be a video on the output itself. Start the series with the first episode, which we’ve placed below the break.

His style is laid-back, making it a restful watch as he builds each circuit on a breadboard and explains its operation with the aid of a multimeter. If this whets your appetite for more on simple op-amps, we looked at the first integrated circuit op-amp back in 2018.

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