D-POINT: A Digital Pen With Optical-Inertial Tracking

November 14, 2023 by 4 Comments

[Jcparkyn] clearly had an interesting topic for their thesis project, and was conscientious enough to write up a chunk of it and release it to the wild. The project in question is a digital pen that uses some neat sensor fusion to combine the inputs from a pen-mounted gyro/accelerometer with data from an optical tracking system provided by an off-the-shelf webcam.

A six degrees of freedom (6DOF) tracking system is achieved as a result, with the pen-mounted hardware tracking orientation and the webcam tracking the 3D position. The pen itself is quite neat, with an ALPS/Alpine HSFPAR003A load sensor measuring the contact pressure transmitted to it from the stylus tip. A Seeed Xaio nRF52840 sense is on duty for Bluetooth and hosting the needed IMU. This handy little module deals with all the details needed for such a high-integration project and even manages the charging of a single 10440 lithium cell via a USB-C connector.

Positional tracking uses Visual Pose Estimation (VPE) assisted with ArUco markers mounted on the end of the stylus. A consumer-grade (i.e. uncalibrated) webcam is all that is required on the hardware side. The software utilizes the familiar OpenCV stack to unroll the effects of the webcam rolling shutter, followed by Perspective-n-Point (PnP) to estimate the pose from the corrected image stream. Finally, a coordinate space conversion is performed to determine the stylus tip position relative to the drawing surface.

The sensor fusion is taken care of with a Kalman filter, smoothed with the typical Rauch-Tung-Striebel (RTS) algorithm before being passed onto the final application. This process is running in Python using the NumPy module, as you would expect, but accelerated using the Numba JIT compiler.

Motion tracking is not news to us, we’ve seen many an implementation over the years, such as this one. But digital input pens? Why aren’t they more of a thing?

Thanks to [Oliver] for the tip!

Pi Zero FPV Robot Uses Tiny Motor & Gears

November 14, 2023 by 4 Comments

We’ve seen plenty of first-person view (FPV) robots built using the Raspberry Pi Zero, but this one from [Shane] has an interesting twist: rather than directly driving the wheels from big motors, it uses small motors and gearboxes to drive the wheels, with some of the gears being 3D printed.

[Shane] has posted the full details of this cute little robot, complete with 3D models, code, and plans for the PCB that connects the Zero to the motors. These motors are N20 ones, which are much smaller and cheaper than what we usually see used in these projects, and run faster. They also often come with a gearbox that reduces the speed to something a bit more useful. Each motor drives the two wheels on one side through a 3D printed gear for tank-style steering.

To run the whole thing off a single LiPo battery, [Shane] also designed his own Pi Hat that converted the voltage to 5 V and added a couple of H bridge chips for the motors. It is a cute little build, but the requirement for a custom Pi hat perhaps puts it beyond most beginners, who might be interested in a cheap, straightforward build like this. Does anybody have any alternatives?

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3D Printed Stamp Rollers

November 13, 2023 by 3 Comments

If you have an artistic bent, you might have seen self-inking stamp rollers. These are like rotary rubber stamps that leave a pattern as you roll across a page. [Becky] wanted a larger custom roller and turned to 3D printing to make it happen. The first prototype used a modified Sharpie. However, she soon moved to an unmodified acrylic marker that had a rectangular tip.

A Tinkercad design produces a cap that fits the marker and a wheel that contains the desired pattern. Text works well, although you can easily do a custom pattern, too, of course.

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Using Nuclear Decay As Random Number Generator Source For An MCU

November 13, 2023 by 1 Comment

Although there are many ways to get a random number generator (RNG) set up on a microcontroller, it’s hard to argue with the sheer randomness of the various kinds of radiation zipping all around us from nuclear decay events. For [gbonacini] the purchase of a Geiger counter first in 2022 was the reason to tinker with using these as the source for an RNG, which simply runs a counter until a Geiger counter event occurs that ‘selects’ a number and the counter is reset to zero.

With the next version of this system the hardware and layout has changed somewhat, using a commercial handheld Geiger counter (GMC-320+) and its audio output as a generic input for any MCU. The (pulsed) audio signal is amplified with an opamp (left unspecified) that connects to a GPIO pin of the MCU (RP2040-based Pico W). Here the same algorithm is used to create a continuous queue of randomly picked numbers, which can also be queried via the WiFi interface with a custom protocol, essentially making it a network-connected RNG that could be used by other network-connected appliances.

C++ source is provided for the Pico W example, but it should be easy enough to adapt to other platforms. The GMC-320+ is also among the more affordable Geiger counters out there, even if it’s somewhat bulky to pair with just a single MCU, making a more basic Geiger counter module better for a permanent installation. Either way you should get pretty good RNG this way without splurging on exotic hardware.

Thanks to [navigator] for the tip.

Obsolete E-Reader Gets New Life

November 13, 2023 by 6 Comments

For those who read often, e-readers are a great niche device that can help prevent eye fatigue with their e-ink displays especially when compared to a backlit display like a tablet or smartphone, all while taking up minimal space unlike a stack of real books. But for all their perks, there are still plenty of reasons to maintain a library of bound paper volumes. For those who have turned back to books or whose e-readers aren’t getting the attention they once did, there are plenty of things to do with them like this e-book picture frame.

The device started life as a PocketBook Basic Touch, or PocketBook 624, a fairly basic e-reader from 2014, but at its core is a decent ARM chip that can do many more things than display text. It also shipped running a version of Linux, which made it fairly easy to get a shell and start probing around. Unlike modern smart phones this e-reader seems to be fairly open and able to run some custom software, and as a result there are already some C++ programs available for these devices. Armed with some example programs, [Peter] was able to write a piece of custom software that displays images from an on-board directory and mounted the new picture display using an old book.

There were a number of options for this specific device that [Peter] explored that didn’t pan out well, like downloading images from the internet to display instead of images on the device, but in the end he went with a simpler setup to avoid feature creep and get his project up and running for “#inktober”, a fediverse-oriented drawing challenge that happened last month. While not strictly in line with a daily piece of hand-drawn artwork, the project still follows the spirit of the event. And, for those with more locked-down e-readers there’s some hope of unlocking the full functionality of older models with this FOSS operating system.

Hot Wheel Car Becomes 1/64 Scale Micro RC Car, Complete With Camera

November 13, 2023 by 20 Comments

If you enjoy watching skilled assembly of small mechanical systems with electronics to match, then make some time to watch [Max Imagination] transform a Hot Wheels car into a 1/64th scale RC car complete with video FPV video feed. To say the project took careful planning and assembly would be an understatement, and the results look great.

The sort of affordable electronics available to hobbyists today opens up all kinds of possibilities, but connecting up various integrated modules brings its own challenges. This is especially true when there are physical constraints such as fitting everything into an off-the-shelf 1/64 scale toy car.

There are a lot of interesting build details that [Max] showcases, such as rebuilding a tiny DC motor to have a longer shaft so that it can drive both wheels at once. We also liked the use of 0.2 mm thick nickel strips (intended for connecting cells in a battery pack) as compliant structural components.

There are actually two web servers being run on the car. One provides an interface for throttle and steering (here’s the code it uses), and the other takes care of the video feed with ESP32-CAM sending a motion jpeg stream. [Max]’s mobile phone is used to control the car, and a second device goes into an old phone-based VR headset to display the FPV video feed.

Circuit diagrams and code are available for anyone wanting to perhaps make a similar project. We’ve seen micro RC builds of high quality before, but integrating an FPV camera kicks things up a notch. Want even more complex builds? All the rules change when weight reduction is a non-negotiable #1 priority. Check out a micro RC plane that weighs under three grams and get a few new ideas.

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Vectorscope KiCad Redrawing Project

November 13, 2023 by 23 Comments

When I saw this year’s Supercon Vectorscope badge, I decided that I had to build one for myself. Since I couldn’t attend in-person, I immediately got the PCBs and parts on order. Noting that the GitHub repository only had the KiCad PCB file and not the associated schematics and project file, I assumed this was because everyone was in a rush during the days leading up to Supercon weekend. I later learned, however, that there really wasn’t a KiCad project — the original design was done in Circuit Maker and the PCB was converted into KiCad. I thought, “how hard can this be?” and decided to try my hand at completing the KiCad project.

Fortunately I didn’t have to start from scratch. The PCB schematics were provided, although only as image files. They are nicely laid out and fortunately don’t suffer the scourge of many schematics these days — “visual net lists” that are neither good schematics nor useful net lists. To the contrary, these schematics, while having a slightly unorthodox top to bottom flow, are an example of good schematic design. Continue reading “Vectorscope KiCad Redrawing Project” →