[mircemk] shows how to create a simple non-contact proximity sensor using little more than an Arduino Nano board, and a convenient software library intended to measure the value of capacitors.

The basic idea is that it’s possible to measure a capacitor’s capacitance using two microcontroller pins and the right software, so by using a few materials to create an open-style capacitor, one can monitor it for changes and detect when anything approaches enough to alter its values past a given threshold, creating a proximity sensor.

The sensor shown here is essentially two plates mounted side-by-side, attached to an Arduino Nano using the Capacitor library which uses just two pins, one digital and one analog.

As configured, [mircemk]’s sensor measures roughly thirty picofarads, and that value decreases when approached by something with a dielectric constant that is different enough from the air surrounding the sensor. The sensor ignores wood and plastic, but an approaching hand is easily detected. The sensor also detects liquid water with similar ease, either in the form of pooled liquid, or filled bottles.

We’ve also seen a spring elegantly used as a hidden touch sensor that works through an enclosure’s wall by using similar principles, so the next time you need a proximity or touch-sensitive sensor in a project, reaching for the junk box might get you where you need to go. Watch [mircemk]’s sensor in action in the video, just below the page break.

The Marimbatron is [Leo Kuipers] ‘s final project as part of the Fab Academy program supervised by [Prof. Neil Gershenfeld] of MIT’s Center for Bits and Atoms. The course aims to teach students how to leverage all the fab lab skills to create unique prototypes using the materials at hand.

Fortunately, one of the main topics covered in the course is documentation, and [Leo] has provided ample material for review. The marimba consists of a horizontal series of wooden bars, each mounted over a metal resonator tube. It is played similarly to the xylophone, with a piano-type note arrangement, covering about five octaves but with a lower range than the xylophone. [Leo] converted this piano-type layout into a more logical grid arrangement. The individual pads are 3D printed in PETG and attached to a DIY piezoresistive pressure sensor made from a graphite-sprayed PET sheet laid upon a DIY flexible PCB. A central addressable LED was also included for indication purposes. The base layer is made of cast polyurethane, formed inside a 3D-printed rigid mould. This absorbs impact and prevents crosstalk to nearby sensors. The sensor PCB was initially prototyped by adhering a layer of copper tape to a layer of Kapton tape and cutting it out using a desktop vinyl cutter. While this method worked for the proof of concept, [Leo] ultimately outsourced the final version to a PCB manufacturer. The description of prototyping the sensor and dealing with over-moulding was particularly fascinating.

For the electronics, a modular approach was needed. Each row of ten sensors was daisy-chained to connect the LEDs, with an individual sense line passed down for each sensor to a common sensor PCB. This uses a SAMD21-series microcontroller with enough ADC channels to handle the task. This was initially prototyped using a micro-milled PCB and a laser-cut PET solder stencil. Once that was proven to work well, the sensible thing was done, and the final PCBs were ordered from a proper fab. Additionally, a user interface PCB was created to host a few pushbuttons and a Waveshare round LCD display. Finally, a main control PCB routes I²C to the sensor boards and interfaces to the SPI LCD. It also handles sending MIDI data over USB for playback on an external MIDI device.

Documentation and design data can both be found on the project fabcloud page. To dig into the Fab Academy courses, wander over to the course archive and get cracking.

This is the first marimba we’ve covered, so here’s a mechanical xylophone instead. Whilst we’re on the subject of mechanical music, here’s a fun one to go back over.

This ultra-cute tiny LiDAR rangefinder project by [gokux] can be thought of as a love letter to the incredible resources and components hobbyists and hackers of all types have access to nowadays. In fact, it all stemmed from coming across a miniscule half-inch 64×32 OLED display module that was simply too slick to pass up.

To use it, one simply powers it on and the display will read out the distance in millimeters. The VL53L0X time-of-flight sensor inside works by sending out a laser pulse and measuring how long it takes for the pulse to bounce back. We hope you’re curious about what such a sensor looks like on the inside, because here’s a nifty teardown of these fantastic devices. The device can technically measure distances of up to 2 m, but [gokux] says accuracy drops off after 1 m.

The main components besides the OLED display and VL53L0X sensor are an ESP32-C3 board (which handily integrates battery charging circuitry), 3D-printed enclosure, tiny rechargeable battery, and power switch. The whole thing is under one cubic inch. Not bad, and it even makes a passable keychain. Parts list, code, and 3D model files, including STEP format, are all available if you’d like to spend an afternoon making your own.

Sometimes, it’s time to shut down the oscilloscope, and break out the cardboard and paints. If you’re wondering what for, well, here’s a reminder of an Instructable from [CrazyScience], that brings us back to cardboard crafts days. They rebuild one of the most iconic components for an electronics tinkering beginner — an ultrasonic distance sensor, and what’s fun is, it stays fully functional after the rebuild!

This project is as straightforward as it gets, describing all the steps in great detail, and you can complete it with just a hot glue gun and soldering iron. With materials being simple cardboard, aluminum foil, popsicle sticks, some mesh, and a single ultrasonic sensor for harvesting the transmitter and receiver out of, this is the kind of project you could easily complete with your kids on a rainy day.

Now, the venerable ultrasonic sensor joins the gallery of classics given a size change treatment, like the 555 timer we’ve seen two different takes on, or perhaps that one Arduino Uno. Unlike these three, this project’s cardboard skeleton means it’s all that simpler to build your own, what’s with all the shipping boxes we accumulate.

As desktop 3D printers have inched towards something resembling the mainstream, manufacturers have upped their game across the board. Even the quality of filament that you can get today is far better than what was on the market in the olden days, back when a printer made out of laser-cut birch wasn’t an uncommon sight at the local makerspace. Now, even the cheap rolls are wound fairly well and are of a consistent diameter. For most folks, you just need to pick a well-reviewed brand, buy a roll, and get printing.

But as with everything else, there are exceptions. Some people are producing their own filaments, or want to make sure their extrusion rate is perfectly calibrated. For those that need the capability, the WInFiDEL from [Sasa Karanovic] can detect filament diameter in real-time while keeping the cost and complexity as low as possible. Even better, with both the hardware and software released as open source, it makes an excellent starting point for further development and customization.

In fact, the WInFiDEL itself was developed from the earlier InFiDEL sensor designed by [Thomas Sanladerer]. This new version uses the same basic mechanism: a pair of bearings, with one fixed in position and the other attached to an arm with a magnet on the end. As the filament passes between the bearings, the arm raises and lowers the magnet, which is detected by a linear Hall-effect sensor. The resulting raw deflection data, once properly calibrated, provides a highly accurate readout of the filament diameter as it passes through the sensor and into the extruder.

What’s changed is how the sensor is utilized. [Thomas] imagined the original sensor as being connected directly to the 3D printer’s motherboard, with its data being used to modify the extrusion rate during printing. In other words, it wasn’t really designed for humans to use. For the WInFiDEL, [Sasa] dropped the anemic ATTiny85 and replaced it with an ESP32 that can connect to your WiFi network and offer up a slick web interface, complete with a easy to use calibration tool and a rolling graph that plots out the data as it comes in. There’s also an API that allows you to hit the sensor with a web request to get current diameter and calibration data should you want to virtually connect it up to something like OctoPrint.

Most of us don’t need the WInFiDEL. But looking at the exceptional hardware and software of this project, we sure as hell want one anyway. Of course, we’d expect no less from [Sasa]. Whether its his OS-agnostic fan controller or ESP32 powered camera slider, his creations always exhibit a sort of simplistic elegance that we’re big fans of.

While split-flap alarm clocks once adorned heavy wood nightstands in strong numbers, today the displays are most commonly found in train stations and airports. Hey, at least they’re still around, right? Like many of us, [The Wrench] has always wanted to make one for themselves, but they actually got around to doing it.

This doesn’t seem like a beginner-friendly project, but [The Wrench] says they were a novice in 3D design and so used Tinkercad to design all the parts. After so many failures, they settled on a design for each unit that uses a spool to attach the flaps, which is turned by a stepper motor.

A small neodymium magnet embedded in the primary gear and a Hall effect sensor determine where the stepper motor is, and in turn, which number is displayed. Everything is handled by an Arduino Nano on a custom PCB.

Aside from the sleek, minimalist look, our favorite part is that [The Wrench] used even more magnets to connect each display segment to the base. You may have noticed that there are only three segments, because the hours are handled by a single display that has flaps for 10, 11, and 12. This makes things simpler and gives the clock an interesting look. Be sure to check out the build video after the break.

Want to build a more complicated clock? Try suspending sand digits in the air with persistence of vision.

Wait a second, read that title again. This isn’t a throwback 3D printing project at all. That’s “RepTrap” as in reptile trap, and it’s a pretty clever way to study our cold-blooded friends in their natural habitat.

Now, game cameras — or trail cameras, if you’re less interested in eating what you see — are pretty much reduced to practice. For not that much money you can pick up one of these battery-powered devices, strap it to a tree, and have it automatically snap high-quality pictures of whatever wildlife happens to wander past. But nearly all of the commercially available game cameras have pyroelectric infrared sensors, which trigger on the temperature difference between a warm-blooded animal and the ambient temperature of the background. But what to do when you’re more interested in cold-blooded critters?

Enter [Mirko], who stumbled upon this problem while working with a conservation group in Peru. The group wanted to study snakes, insects, and other ectothermic animals, which are traditionally studied by trapping with pitfalls and other invasive techniques. Unable to rely on PIR, [Mirko] rigged up what amounts to a battery-powered light curtain using a VL53L4CD laser time-of-flight sensor. Mounted above the likely path of an animal, the sensor monitors the height of everything in its field of view. When an animal comes along, cold-blooded or otherwise, RepTrap triggers a remote camera and snaps a picture. Based on the brief video below, it’s pretty sensitive, too.

[Mirko] started out this project using an RP2040 but switched to an ESP32 to take advantage of Bluetooth camera triggering. The need for weatherproofing was also a big driver for the build; [Mirko] is shooting for an IP68 rating, which led to his interesting use of a Hall sensor and external magnet as a power switch.