Soil Moisture Sensors, How Do They Work?

May 17, 2021 by Donald Papp 19 Comments

In a way, the magic of a soil moisture sensor’s functionality boils down to a simple RC circuit. But of course, in practice there is a bit more to it than that. [rbaron] explains exactly how capacitive soil moisture sensors work simply, clearly, and concisely. He also shows, with a short video, exactly how their output changes in response to their environment, and explains how it informed his own sensor design.

At its heart, a moisture sensor measures how quickly (or slowly) a capacitor charges through a resistor, but in these sensors the capacitor is not a literal component, but is formed by two PCB traces that are near one another. Their capacitance — and therefore their charging rate — changes in response to how much water is around them. By measuring this effect on a probe sunk into dirt, the sensor can therefore indirectly measure the amount of water in the soil.

This ties into his own work on b-parasite: an open-source, all-in-one wireless soil moisture sensor (which was also a runner-up in our Earth Day contest) that broadcasts over BLE and even includes temperature readings. One thing to be mindful of if you are making your own PCBs or ordering them from a fab house is that passing current through metal in a moist environment is a recipe for oxidation, so it’s important not to expose bare traces to wet soil. A good coated PCB should avoid this problem, but one alternative we have seen proposed is to use graphite rods in place of metal.

3D-Printed Desiccant Container Exploits Infill

May 11, 2021 by Donald Papp 15 Comments

Desiccant is common in 3D printing because the drier plastic filament is, the better it prints. Beads of silica gel are great for controlling humidity, but finding a porous container for them that is a convenient size is a little harder. 3D printing is a generally useful solution for custom containers, but suffers from a slight drawback in this case: printing dense grills or hole patterns is not very efficient for filament-based printers. Dense hole patterns means lots of stopping and starting for the extruder, which means a lot of filament retractions and longer print times in general.

The green model is used as a modifier to the orange container (of which only the corners are left visible here)

[The_Redcoat]’s solution to this is to avoid hole patterns or grills altogether, and instead print large wall sections of the container as infill-only, with no perimeter layers at all. The exposed infill pattern is dense enough to prevent small beads of desiccant from falling through, while allowing ample airflow at the same time. The big advantage here is that infill patterns are also quite efficient for the printer to lay down. Instead of the loads of stops and starts and retractions needed to print a network of holes, infill patterns are mostly extruded in layers of unbroken lines. This translates to faster print speeds and an overall more reliable outcome, even on printers that might not be as well tuned or calibrated as they could be.

To get this result, [The_Redcoat] modeled a normal, flat-walled container then used OpenSCAD to create a stack of segments to use as a modifier in PrusaSlicer. The container is printed as normal, except where it intersects with the modifier, in which case those areas get printed with infill only and no walls. The result is what you see here: enough airflow for the desiccant to do its job, while not allowing any of the beads to escape. It’s a clever use of both a high infill as well as the ability to use a 3D model as a slicing modifier.

There’s also another approach to avoiding having to print a dense pattern of holes, though it is for light-duty applications only: embedding a material like tulle into a 3D print, for example, can make a pretty great fan filter.

Commodore 64 Emulator In VR Delivers A Full 80s Experience

May 3, 2021 by Donald Papp 18 Comments

The simulated color CRT monitor looks surprisingly convincing in VR.

One way to play with vintage hardware without owning the hardware is to use an emulator, but [omni_shaNker] announced taking it to the next level by using VR to deliver a complete Commodore 64 system, in its full glory, complete with a native 80s habitat playset! This is a pretty interesting angle for simulating vintage hardware, especially since the emulator is paired with what looks like a pretty convincing CRT monitor effect in VR, not to mention a virtual 5.25″ floppy drive that makes compellingly authentic sounds.

The project is hosted on GitHub and supports a variety of VR hardware, but for owners of Oculus headsets, the application is also available on SideQuest for maximum convenience. SideQuest is essentially an off-the-books app store for managing software that is neither approved nor distributed by Facebook. Oculus is owned by Facebook, and Facebook is keen to keep a tight grip on their hardware.

As functional as the application is, there are still improvements and optimizations to be made. To address this, [omni_shaNker] put out a call for beta testers on Reddit, so if that’s up your alley be sure to get in touch. A video demonstration and overview that is chock-full of technical details is also embedded below; be sure to give it a watch to see what the project is all about.

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Looks Like A Pi Zero, Is Actually An ESP32 Development Board

April 30, 2021 by Donald Papp 34 Comments

ATMegaZero ESP32- S2, showing optional color-coded 40-pin header (top)

The ATMegaZero ESP32-S2 is currently being funded with a campaign on GroupGets, and it’s a microcontroller board modeled after the Raspberry Pi Zero’s form factor. That means instead of the embedded Linux system most of us know and love, it’s an ESP32-based development board with the same shape and 40-pin GPIO header as the Pi Zero. As a bonus, it has some neat features like a connector for inexpensive SSD1306 and SH1106-based OLED displays.

Being able to use existing accessories can go a long way towards easing a project’s creation, and leveraging that is one of the reasons for sharing the Pi Zero form factor. Ease of use is also one of the goals, so the boards will ship with CircuitPython (derived from MicroPython), and can also be used with the Arduino IDE.

If a microcontroller board using the Pi Zero form factor looks a bit familiar, you might be remembering the original ATMegaZero which was based on the Atmel ATMega32U4, but to get wireless communications one needed to attach a separate ESP8266 module. This newer board keeps the ATMegaZero name and footprint, but now uses the Espressif ESP32-S2 to provide all the necessary functions.

CircuitPython has been a feature in a wide variety of projects and hacks we’ve seen here at Hackaday, and it’s a fine way to make a microcontroller board easy to use right out of the box.

This DIY Split-Flap Display Does Both Time And Weather

April 29, 2021 by Donald Papp 5 Comments

With little more than four economical stepper motors, a Raspberry Pi Zero, and a 3D printer, [Thomas Barlow] made himself an awfully slick Smart Flip Clock that can display not only the time, but also weather data as well. This is done by adding a few extra graphics to some of the split-flaps, so numbers can also be used to indicate temperature and weather conditions succinctly. Displaying the time has to do without a colon (so 5:18 displays as 518), but being able to show temperature and weather conditions more than makes up for it.

According to the project’s GitHub repository, it looks as though each split-flap has thirteen unique positions. The first ten are for numerals 0 through 9, and the rest are either blank, or used to make up a few different weather icons with different combinations. A Python script runs on the Raspberry Pi and retrieves weather data from OpenWeather, and the GPIO header drives the display via four geared stepper motors and driver boards. The rest of the hardware is 3D printed, and [Thomas] helpfully provides CAD models in STEP format alongside the STL files.

The basic design of a split-flap display is really quite versatile, and enterprising hackers have been putting delightful new twists on them for years. There has been a split-flap display used as a kind of flip-book animation, and we’ve also had the pleasure of seeing an entire Tarot deck used for esoteric, automated readings.

Faux Stained Glass Effect, With 3D Printing And Epoxy

April 22, 2021 by Donald Papp 14 Comments

Like the looks of stained glass, but not the amount of work, skill, and materials involved? Well, [Northern Geometry] shows how to sidestep all that nonsense and use a 3D printed frame, epoxy, and some alcohol-based inks to create a pretty good fake stained-glass effect piece of art.

A smooth polypropylene board is the key to a glassy smooth back.

[Northern Geometry] has played with this idea before, but shares some refinements and tips on getting the best results. One suggestion is to begin by securely taping the 3D printed frame to a smooth polypropylene board as a backer. Giving the cured resin a smooth surface is important to get the right look, and since resin will not bond to the polypropylene, it can be used as a backer to get that done.

Once the frame is mounted, pour a small amount of epoxy into each cavity and ensure it gets into every corner, then let it cure. The thin bottom layer of resin will seal things as well as create a glassy-smooth backing that is the perfect foundation for finishing the piece with colored resin as needed.

Once that is done, and everything has had plenty of time to cure fully, just pop the piece off the board. Check it out in the video embedded below, where [Northern Geometry] shows the process from start to finish.

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What To Expect From 3D Scanning, And How To Work With It

April 20, 2021 by Donald Papp 19 Comments

3D scanning and 3D printing may sound like a natural match for one another, but they don’t always play together as easily and nicely as one would hope. I’ll explain what one can expect by highlighting three use cases the average hacker encounters, and how well they do (or don’t) work. With this, you’ll have a better idea of how 3D scanning can meet your part design and 3D printing needs.

How Well Some Things (Don’t) Work

Most 3D printing enthusiasts sooner or later become interested in whether 3D scanning can make their lives and projects easier. Here are a three different intersections of 3D scanning, 3D printing, and CAD along with a few words on how well each can be expected to work.

Goal	Examples and Details	Does it work?
Use scans to make copies of an object.	3D scan something, then 3D print copies. Objects might be functional things like fixtures or appliance parts, or artistic objects like sculptures.	Mostly yes, but depends on the object
Make a CAD model from a source object.	The goal is a 1:1 model, for part engineering purposes. Use 3D scanning instead of creating the object in CAD.	Not Really
Digitize inconvenient or troublesome shapes.	Obtain an accurate model of complex shapes that can’t easily be measured or modeled any other way. Examples: dashboards, sculptures, large objects, objects that are attached to something else or can’t be easily moved, body parts like heads or faces, and objects with many curves. Useful to make sure a 3D printed object will fit into or on something else. Creating a CAD model of a part for engineering purposes is not the goal.	Yes, but it depends

In all of these cases, one wants a 3D model of an object, and that’s exactly what 3D scanning creates, so what’s the problem? The problem is that not all 3D models are alike and useful for the same things.

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