A microwave imaging setup. On the left is a monitor displaying a monochrome GUI. In the center is the RP2040-based positioning and measurement system, and on the right is a vector network analyzer.

Precise Positioning With The RP2040

January 1, 2024 by Stephen Ogier 10 Comments

Microwave imaging is similar to CT imaging, but instead of X-rays, the microwaves are used to probe the structure and composition of an object. To facilitate experimentation with microwave imaging, [Zehao Li] and [Kapil Gangwar] developed a system based on the RP2040 to control the height and rotation of a test object.

Their control system has a refreshingly physical user interface—a keypad. The keypad is used to configure the object’s position and the scanning step size, while user menus and the sample position are displayed in a clean and uncluttered interface over VGA. The RP2040 runs a multi-threaded program to handle user input, VGA display, and precise driving of two stepper motors for sample positioning.

The microwave imaging was performed by measuring the RF transmission over 2.5-8 GHz between two Vivaldi antennas on either side of the sample at a variety of angles. 2D cross-sections of the test object were reconstructed in Matlab using filtered back-projection. In this proof-of-concept demonstration, a commercial vector network analyzer was used to collect the data, but one could imagine migrating to a software defined radio (SDR) in the future.

A video demonstrating the system is embedded below the break. If you’re interested in DIY radio imaging, you might be interested in this guide to building your own synthetic aperture radar setup, or this analysis of an automotive radar chip.

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An exploded view render of a red 3D printed case with a green PCB is inside with visible USB-A connectors with a mouse and keyboard graphic above each and "A" and "B" labels above USB-C connectors on the other side.

Building A Better Keyboard And Mouse Switch

December 26, 2023 by Navarre Bartz 38 Comments

Switching inputs between desktops seems like something that should be simple but can prove to be a pain in reality. [Hrvoje Cavrak] decided to take matters into his own hands and build a better keyboard and mouse switch.

DeskHop is built from two Raspberry Pi Pico boards connected via UART and separated by an Analog Devices ADuM1201 dual-channel digital isolator. Through the magic of Pico-PIO-USB these RP2040s can be both host and device. To keep things simple, the PCB is single-sided, and the BOM only has five distinct components.

Once hooked up to your Windows, Mac, or Linux device, your mouse pointer “magically” goes from one screen to the other when dragged across the screen edge. Keyboard LEDs can be reprogrammed to indicate which device is active, and the real beauty of the device is that since it’s a hardware solution, you don’t have to install any software on a computer you might not have admin access to.

If you want to see some more ideas for keyboard and mouse switching, check out this Pi KVM with ATX signaling, this USB triplexer, or this Pi KVM on a PCIe card.

Zerowriter Promises Zero Distractions While Writing

December 21, 2023 by Kristina Panos 15 Comments

As great as full-blown desktop computers may be for web surfing, gaming, and what have you, they are theaters of distraction when it comes time to write. And while there are machines out there purpose-built for writing, the price tags run awfully high for what they are, which is essentially a microprocessor handling a keyboard and an E-ink display.

So, why not build one yourself, then? That’s the idea behind the Zerowriter, which, as you may have guessed, is based on the Raspberry Pi Zero. The Zero 2 W to be exact: [zerowriter] says that the extra power over the original Zero is quite useful.

In addition, there’s a 4.2″ Waveshare E-ink display and the Vortex Core 40% keyboard inside the 3D-printed enclosure. The design is based on the Penkesu computer, although in the Zerowriter, the Pi sits behind the screen instead of underneath the keyboard. [zerowriter] built an application on top of the Waveshare demo program that’s easy to use and modify.

The price tag for this build comes in around $200, which is a fraction of similar commercial products. Most of the cost is in this particular keyboard, although 40%s are, broadly speaking, not cheap. We would love to see someone make a keyboard for this.

Looking to make something a bit bigger? Be sure to check out the MUSE.

Parachute Drops Are Still A Viable Solution For Data Recovery From High Altitude Missions

December 19, 2023 by Lewin Day 12 Comments

Once upon a time, when the earliest spy satellites were developed, there wasn’t an easy way to send high-quality image data over the air. The satellites would capture images on film and dump out cartridges back to earth with parachutes that would be recovered by military planes.

It all sounds so archaic, so Rube Goldberg, so 1957. And yet, it’s still a viable method for recovering big globs of data from high altitude missions today. Really, you ask? Oh, yes indeed—why, NASA’s gotten back into the habit just recently!

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When Is A Typewriter A Printer? When It Has A Parallel Port

December 14, 2023 by Kristina Panos 13 Comments

If you want to talk to a typewriter using something other than your fingers on the keys, you could do a lot worse than to pick up a specimen featuring a Centronics parallel port. That’s what happened to [mlupo], who came across an old Swintec 1146 CMP and decided to hack it into an art installation.

At the push of a giant, clicky button, the typewriter now spits out family stories. This is all thanks to an Adafruit KB2040 keyboard driver being used in a new, exciting way — as a printer driver.

More specifically, the CircuitPython program running on the KB2040 takes in a text file and then sends the data one character at a time until a newline is reached. At that point, the typewriter sends a busy signal and the characters are typed.

As soon as the typewriter is no longer occupied, the data stream picks back up until the next newline or until the file is completely typed out.

Once [mlupo] figured out enough of the parallel port protocol, they were able to build a custom breakout board with the KB2040, a female parallel port, and a row of LEDs for debugging that [mlupo] kept because they look cool.

The KB2040 sets the values high on a series of the parallel port’s data pins, along with the port’s STROBE pin, which pulls low when data is ready. During each STROBE cycle, the high and low pins are read by the Swintec as a binary character.

Of course, you can always use the power of Pi to build your own modern typewriter.

Thanks to [foamyguy] for the tip!

DIY Tachistoscope Feeds Your Hunger For Popcorn And Propaganda

December 13, 2023 by Dan Maloney 12 Comments

You’ve probably heard of subliminal advertising — the idea is that behaviors can be elicited by flashing extremely brief messages on a movie or TV screen. “BUY POPCORN NOW” is the canonical example, with movies containing such subconscious messaging supposedly experiencing dramatic increases in popcorn sales.

Did it work? Maybe, maybe not, but the idea is intriguing enough to at least explore using this subliminal tachistoscope. [Roni Bandini] seems to have taken this project on as a sort of cautionary tale about brainwashing techniques, not only in motion pictures and TV but in printed media too; he goes pretty hard on the Peronistas’ use of not-so-subliminal messages to mold young Argentinian minds back in the 1940s and 50s.

The tachistoscope [Roni] presents is a little more sophisticated than those ham-fisted propaganda attempts. The Raspberry Pi-powered device downloads a video from YouTube and automatically replaces random frames with a propaganda message inspired by those used by the Peronistas, with the modified video piped to a composite video output for display on a TV.

A digital counter on the tachistoscope keeps track of the total time viewers have been propagandized. For extra fun, the machine has a switch to enable ChatGPT-created political messages to be inserted into the stream; we shudder to think what those might look like. Watch the video below for a sample of the brainwashing, but don’t blame us if you fall in love with [Evita].

We understand that this is more of a statement on the power of propaganda than an actual tool for mind control, but if [Roni] is serious about his brainwashing, some small mods might make it more effective. Thanks to the full frame of text on a black background, the subliminal messages aren’t very subliminal; they might be more subtle if the text was overlaid on the target frame rather than replaced completely. Seems like that should be possible with ffmpeg or something similar.

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Raspberry Pi Changes HATs

December 11, 2023 by Jenny List 22 Comments

Following on the heels of their Raspberry Pi 5 launch and some specifications for their RP1 all-in-one peripheral chip, the Raspberry Pi folks have now released an update to the HAT peripheral hardware specification reflecting the new model. Called the HAT+, it represents a major step forward with some significant changes.

Most visible will be changes to the mechanical specification, for while the original HAT specification was very rigid this new version is much looser. A HAT+ must only mate with the 40-pin connector, including the ID pins, and line up with only a single mounting hole compared to the four on the original. Electrically, a HAT+ must recognise the standby power state in which the 3.3-volt line is powered down while the 5-volt line remains active, while software-wise, there are changes to the content of the ID EEPROM including the ability to inform about stackable smaller HATs.

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