A UV Meter For The Flipper Zero

May 19, 2025 by Matt Varian 6 Comments

We all know UV radiation for its contributions to getting sunburned after a long day outside, but were you aware there are several types different types of UV rays at play? [Michael] has come up with a Flipper Zero add on board and app to measure these three types of radiation, and explained some of the nuances he learned about measuring UV along the way.

At the heart of this project is an AS7331 sensor, it can measure the UV-A, UV-B, and UV-C radiation values that the Flipper Zero reads via I2C. While first using this chip he realized to read these values is more complex than just querying the right register, and by the end of this project he’d written his own AS7331 library to help retrieve these values. There was also a some experimenting with different GUI designs for the app, the Flipper Zero screen is only 128x64px and he had a lot of data to display. One feature we really enjoyed was the addition of the wiring guide to the app, if you install this Flipper Zero app and have just the AS7331 sensor on hand you’ll know how to hook it up. However if you want he also has provided the design files for a PCB that just plugs into the top of the Flipper Zero.

Head over to his site to check out all the details of this Flipper Zero project, and to learn more about the different types of UV radiation. Also be sure to let us know about any of your Flipper Zero projects.

Reading The Color Of Money

May 11, 2025 by Matt Varian 9 Comments

Ever wondered what happens when you insert a bill into a vending machine? [Janne] is back with his latest project: reverse engineering a banknote validator. Curious about how these common devices work, he searched for information but found few resources explaining their operation.

To learn more, [Janne] explored the security features that protect banknotes from counterfeiting. These can include microprinting, UV and IR inks, holograms, color-shifting coatings, watermarks, magnetic stripes, and specialty paper. These features not only deter fraud but also enable validators to quickly verify a bill’s authenticity.

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Boxie – A Gameboy-Esque Audio Player

May 11, 2025 by Matt Varian 8 Comments

This little audiobook player is a stellar example of the learning process behind a multifaceted project blending mechanical, electrical, and software design. [Mario] designed this audiobook player, dubbed Boxie, for his 3-year-old son to replace the often-used but flawed Toniebox.

The inspiration for Boxie was the Toniebox, a kid-friendly audiobook player. While functional, the Toniebox had drawbacks: it required internet connectivity, limited media selection, and had unreliable controls. Enter Boxie, a custom-built, standalone audiobook player free from web services, designed to address these issues with superior audio quality and toddler-friendly controls.

Boxie’s media is stored on microSD cards inserted into a slot on the device. To make this manageable for a toddler, he designed a PCB with a standard microSD card interface, ensuring easy swapping of audiobooks. The enclosure, crafted via 3D printing, is durable and compact, tailored for small hands.

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Creative PCB Business Cards Are Sure To Make An Impression

May 5, 2025 by Matt Varian 8 Comments

Business cards are a simple way to share contact information, but a memorable design can make them stand out. [Jeremy Cook] has been experimenting with adding artistic finishes to PCBs, and has recently applied what he’s learned to make some unique business cards. His write-up consolidates some great resources to get you started in making your own PCB business cards, as well as PCB art in general

To make his cards stand out, he designed them to serve as functional tools beyond sharing contact information. He created two designs: one incorporates an LED and a coin cell battery holder, while the other includes drafting tools, such as a ruler, circle stencils, and a simplified protractor.

While the classic PCB solder mask is green, many board houses now offer alternative finishes and colors to enhance designs. He tested and compared the offerings from various manufacturers, highlighting the importance of researching fabrication options early, as different providers offer a variety of finishes. His creative approach shines in details like using through-hole pads as eyes in a robot illustration, making them stand out against a halftone dot pattern.

If you’re looking for more inspiration, be sure to check out the winners of our 2024 Business Card Challenge.

Pinoutleaf: Simplifying Pinout References

May 2, 2025 by Matt Varian 10 Comments

We all appreciate clear easy-to-read reference materials. In that pursuit [Andreas] over at Splitbrain sent in his latest project, Pinoutleaf. This useful web app simplifies the creation of clean, professional board pinout reference images.

The app uses YAML or JSON configuration files to define the board, including photos for the front and back, the number and spacing of pins, and their names and attributes.For example, you can designate pin 3 as GPIO3 or A3, and the app will color-code these layers accordingly. The tool is designed to align with the standard 0.1″ pin spacing commonly used in breadboards. One clever feature is the automatic mirroring of labels for the rear photo, a lifesaver when you need to reverse-mount a board. Once your board is configured, Pinoutleaf generates an SVG image that you can download or print to slide over or under the pin headers, keeping your reference key easily accessible.

Visit the GitHub page to explore the tool’s features, including its Command-Line Interface for batch-generating pinouts for multiple boards. Creating clear documentation is challenging, so we love seeing projects like Pinoutleaf that make it easier to do it well.

EclairM0, The Pocket Notepad

April 28, 2025 by Matt Varian 6 Comments

Roughly the size of a Tic Tac container, this project packs a punch in a compact package. [Matt] sent in this beautifully documented pocket device that brings back great memories of texting on early cellphones.

The EclairM0’s firmware is written in TinyGo, a language he hadn’t used before but found perfect for a microcontroller project where storage space is tight. The 14-button input mimics early phone keypads, using multi-tapping and combo key presses to offer various functions. The small SSD1306 OLED display is another highlight. Building on an earlier CircuitPython project, [Matt] optimized the screen’s performance, speeding up its response time for a snappy user experience. The battery picked was only 3 mm thick, however the protection circuity on the battery added another 2 mm so he moved that protection circuity to the main PCB itself to keep it as thin as initially planned.

Weighing just 15 grams, this lightweight device runs on a SAMD21 microcontroller, which supports USB host functionality. This allows the EclairM0 to act as a keyboard, mouse, or even USB peripherals. Housed in a 3D-printed case, the entire project is open-source, with design and firmware files available on GitHub.

We love small handheld projects around here and this well-documented, fun pocket device is no exception, if you want your own he has a page dedicated to helping you build a EclairM0.

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The Mohmmeter: A Steampunk Multimeter

April 24, 2025 by Matt Varian 12 Comments

[Agatha] sent us this stunning multimeter she built as a gift for her mom. Dubbed the Mohmmeter — a playful nod to its ohmmeter function and her mom — this project combines technical ingenuity with heartfelt craftsmanship.

At its core, a Raspberry Pi Pico microcontroller reads the selector knob, controls relays, and lights up LEDs on the front panel to show the meter’s active range. The Mohmmeter offers two main measurement modes, each with two sub-ranges for greater precision across a wide spectrum.

She also included circuitry protections against reverse polarity and over-voltage, ensuring durability. There was also a great deal of effort put into ensuring it was accurate, as the device was put though its paces using a calibrated meter as reference to ensure the final product was as useful as it was beautiful.

The enclosure is a work of art, crafted from colorful wooden panels meticulously jointed together. Stamped brass plates label the meter’s ranges and functions, adding a steampunk flair. This thoughtful design reflects her dedication to creating something truly special.

Want to build a meter for mom, but she’s more of the goth type? The blacked-out Hydameter might be more here style.