Practical Wireless “Tele-Tennis” Build After Only 34 Years

May 30, 2022 by Dave Rowntree 8 Comments

Back in November 1974 the publication “Practical Wireless” produced a five-part article series showing the reader how to construct a version of the popular “pong” game that could be played on the television screen available in the typical British home. [Grant Searle] had wanted to build this project for years, but it took him until 2008 to find the opportunity to do so. The magazine article printed PCB layouts to 1:1 scale, with a bill of materials and assembly instructions. After each month, the reader would have an assembled the project a little more, with the final month dedicated to point-to-point wiring and final setup. Subsequent months contained some enhancements such as a scoring system and sound effects, but these are not yet part of the main build. In order to understand the build, you will need to download the PDF copy of the magazines prints. (And if you’re an electronics nerd like this scribe, you’ve already done that right?)

A tidy assembly job with an authentic retro style

The electronics are based upon pure discrete 7400-series logic, 741 opamp-based ramp generators and, you guessed it, 555 timers. The way the various boards have discrete functions is particularly interesting. For example, in part 3, the PCB described (board A) not only is the master field/line sync generator, but also generates the video signals for the ball, with its position and size determined in an analogue fashion. Signals coming into the board from Board C (top/bottom base) cause a discrete flip-flop to toggle, changing the ball’s direction as it ‘bounces’ off the edge of the screen. Each board generates its own video signal, which are then all combined in the final video mixer (board E) that simply wire-OR’s them all with the composite sync to generate the composite video needed. This would have been tapped off and fed to a UHF video modulator, but [Grant] chose not to install that for the build. The whole thing was wrapped up inside an MDF case, coated in that dubious fake-wood plastic wrap, for that very 70’s aesthetic some of us remember fondly.

Pong is such a popular classic game, that we’ve covered many, many variants over the years. Here’s one that’s purely mechanical, another that uses the original PCB with a visually appealing twist, and finally, a completely virtual simulation of the original arcade circuit, courtesy of Falstad. We’re sure there will be many more to come.

Thanks [JohnU] for the tip!

Tame Your Flexible Filaments With This Belt-Drive Extruder

May 25, 2022 by Dave Rowntree 8 Comments

[Proper Printing] clearly enjoys pushing the boundaries of 3D printed materials, and sometimes this requires building custom 3D printers or at least the business end of them. Flexible filaments can be a bit of a pain to deal with, simply because most extruders are designed to push the filament into the hot end with a simple hobbed bolt (or pinch roller setup) and only work reliably due the rigidity of the plastic itself. Once you go flexible, the rigidity is reduced and the filament often deflects sideways and the extruder jams. The longer the filament path leading to the hotend, the harder it gets. The dual belt drive extruder (they’re calling it ‘proper extruder’) grips the filament on two sides with a pair of supported belts, guiding it into the hotend without allowing it to deflect sideways. The extruder body and gears were resin printed (but, we checked — the design is suitable for FDM printing as well) proving that resin printing on modern printers, does indeed maintain adequate dimensional accuracy allowing the building of mechanisms, despite the naysayers! Continue reading “Tame Your Flexible Filaments With This Belt-Drive Extruder” →

Learn By Doing: Turn Your Garage Into Your Perfect Workspace

May 16, 2022 by Dave Rowntree 32 Comments

Plenty of potential, but a cozy hacking space it is not

To us hackers and makers, the tools of our trade are often as important and interesting as the details of the hacks themselves, but what about the most important tool of all — the very space you use to make your magic happen? That may be your bedroom, a nearby hackerspace, and if you have the resources, you may even own a place of your own, and get to build your perfect workspace.

The latter situation is what [MichD] and partner [Brittany] found themselves in, having moved into their first place. Many couples focus on getting a hot tub in the garden or sorting the nursery, but these two are proper electronics nerds, so they converted a free-standing double wide garage into the nerdhub, learning as they went along, and documenting it in excruciating detail for your viewing pleasure.

Door fitted, framed up, and insulation in place. All ready for plasterboarding.

The building structurally is a single-skinned brick-built box, with a raw concrete floor. Pretty typical stuff for the UK (we’ve seen much worse), but not ideal for spending an extended amount of time in due to our damp, cold climate, at least in winter.

The first order of business was partitioning the front section for bike storage, and screeding the floor. Once the floor was solid, the walls and ceiling joists could be framed up, ready for fitting insulation material and covering with plasterboard.

Electrics were next in order, with the wires clipped to the brickwork, well away from where the plasterboard would be, therefore making it less likely to accidentally drill into a live cable when adding external fixtures.

Since the front part of the room was to be partitioned off, another access door was needed. This involved cutting out the bricks to fit a concrete lintel. With that installed, and the bricks above supported, the area below was cut out to the required shape. A somewhat nerve-wracking experience, if you ask us!

As any self-respecting hacker will tell you — no room build is complete without a decent amount of RGB bling, so the whole room was decked out with APA102 addressable LED strips. Control of these was courtesy of WLED running on an ESP32 module, with LedFX used on a nearby PC to perform music visualisation, just because.

Already got your space worked out, but need a little help with organisation? Not got much space, and need a portable solution? Check this out for (small) size!

3D Printing Hack Leverages Vase Mode Structurally

May 15, 2022 by Dave Rowntree 25 Comments

Conceptually, FDM 3D printing is quite a simple process: you define a set of volumes in 3D space, then the slicing software takes a cut through the model at ever-increasing heights, works out where the inner and outer walls are, and then fills in the inside volume sparsely in order to tie the walls together and support the top layers that are added at the end.

But as you will find quite quickly, when models get larger and more complex, printing times can quickly explode. One trick for large models with simple shapes but very low structural needs is to use so-called ‘vase mode’, which traces the outline of the object in a thin, vertical spiral. But this is a weak construction scheme and allows only limited modelling complexity. With that in mind, here’s [Ben Eadie] with a kind-of halfway house technique (video, embedded below) that some might find useful for saving on printing time and material.

This solid shape is mostly cut-through to make supporting ribs between the walls of the shell

The idea is to use vase mode printing, but by manipulating the shell of the model, adding partially cut-through slots around the perimeter, and critically, adding one slot that goes all the way.

First you need a model that has an inner shell that follows the approximate shape of the outer, which you could produce by hollowing out a solid, leaving a little thickness. By making the slot width equal to half the thickness of the nozzle size and stopping the slots the same distance from the outer shell, vase mode can be used to trace the outline of shape, complete with supporting ribs in between the inner and outer walls of the shell.

Because the slot is narrower than the extrudate, the slot walls will merge together into one solid rib, tying the objects’ walls to each other, but critically, still allowing it to be printed in a continuous spiral without any traditional infill. It’s an interesting idea, that could have some merit.

There are other ways to stiffen up thing printed parts, such as using surface textures, But if you’re fine with the thin shell, but want to have a little fun with it, you can hack the g-code to make some really interesting shapes.

Continue reading “3D Printing Hack Leverages Vase Mode Structurally” →

TapType: AI-Assisted Hand Motion Tracking Using Only Accelerometers

May 14, 2022 by Dave Rowntree 16 Comments

The team from the Sensing, Interaction & Perception Lab at ETH Zürich, Switzerland have come up with TapType, an interesting text input method that relies purely on a pair of wrist-worn devices, that sense acceleration values when the wearer types on any old surface. By feeding the acceleration values from a pair of sensors on each wrist into a Bayesian inference classification type neural network which in turn feeds a traditional probabilistic language model (predictive text, to you and I) the resulting text can be input at up to 19 WPM with 0.6% average error. Expert TapTypers report speeds of up to 25 WPM, which could be quite usable.

Details are a little scarce (it is a research project, after all) but the actual hardware seems simple enough, based around the Dialog DA14695 which is a nice Cortex M33 based Bluetooth Low Energy SoC. This is an interesting device in its own right, containing a “sensor node controller” block, that is capable of handling sensor devices connected to its interfaces, independant from the main CPU. The sensor device used is the Bosch BMA456 3-axis accelerometer, which is notable for its low power consumption of a mere 150 μA.

User’s can “type” on any convenient surface.

The wristband units themselves appear to be a combination of a main PCB hosting the BLE chip and supporting circuit, connected to a flex PCB with a pair of the accelerometer devices at each end. The assembly was then slipped into a flexible wristband, likely constructed from 3D printed TPU, but we’re just guessing really, as the progression from the first embedded platform to the wearable prototype is unclear.

What is clear is that the wristband itself is just a dumb data-streaming device, and all the clever processing is performed on the connected device. Training of the system (and subsequent selection of the most accurate classifier architecture) was performed by recording volunteers “typing” on an A3 sized keyboard image, with finger movements tracked with a motion tracking camera, whilst recording the acceleration data streams from both wrists. There are a few more details in the published paper for those interested in digging into this research a little deeper.

The eagle-eyed may remember something similar from last year, from the same team, which correlated bone-conduction sensing with VR type hand tracking to generate input events inside a VR environment.

Continue reading “TapType: AI-Assisted Hand Motion Tracking Using Only Accelerometers” →

Monochrome LCD Video Hacks Galore!

May 12, 2022 by Dave Rowntree 23 Comments

[Wenting Zhang] is clearly a fan of old school STN LCD displays, and was wondering how various older portable devices managed to drive monochrome LCDs panels with multiple grey levels. If the display controller supports multiple bits per pixel, it can use various techniques, such as PWM, in order to produce a pseudo-grayscale image. But, what if you have a monochrome-only display controller? With a sufficiently high pixel clock, can you use software on the application side of things to flip those pixels in such a manner as to give a reasonable looking grayscale image?

Simple dithering – don’t look too close!

PDM greyscale approximation in a 1-bit display

[Wenting] goes through multiple techniques, showing the resulting image quality in a clear, systematic manner. The first idea is to use a traditional dithering technique. For each pixel, it is set to black if the grey value is below some threshold. The resulting error value, is then propagated to neighbouring pixels. This error diffusion process smears the error out over the whole display, so spatially speaking, on average the pixel values correspond roughly to the original gray values. But, the pixels themselves are still either on or off. This isn’t quite enough. The next idea is to PWM the individual pixels over multiple frames, to approximate different grey levels. But, that gives a worst case effective refresh rate of 8 Hz with a PWM period of 15 frames, at 120 fps, and that flickers. Badly. One way to mitigate that is to switch to PDM (pulse density modulation) which selects different length sequences to give the same duty cycle but at higher frequency, at least for some grey values. Slightly better, but there’s more that can be done. Continue reading “Monochrome LCD Video Hacks Galore!” →

3D Print Finishing By Spraying Glazing Putty

May 10, 2022 by Dave Rowntree 19 Comments

Finishing off 3D prints is a labour-intensive process, and getting a good looking, smooth surface suitable for painting takes a lot of time and plenty of practice. Deeper printing layer lines or minor surface defects can be smoother over with a variety of materials, from putties to resins, but the deeper the defect, the thicker the filler and that takes it toll on the surface details – smoothing those out and making fine details less distinct. [Darkwing dad] has another solution that looks pretty easy to achieve, by mixing acetone with glazing putty it can be airbrushed over the print surface in one go. After a little experimentation with the ratio of putty to acetone, a wide open nozzle and a low pressure, it was found that a nice even spray could be achieved. Importantly it dries in just a few minutes, enabling multiple coats to be applied in a short space of time.

Once sufficient thickness has been applied, the coating can easily sanded to get a smooth result with the worst of the gaps filled, and the layer lines nicely hidden. The final part of the filling process is more typical, with a few coats of filler primer applied straight from a rattle can, followed by a light sand and you’re good for painting.

We’ve covered smoothing 3D prints practically as long as we’ve been covering 3D printing itself, and there are multiple ways to do this, depending on the filament material, your budget and you tolerance for noxious fumes. Here’s a guide for smoothing using UV curable resins, using a special smoothable filament with IPA, and finally if this is just too fancy, smelly or expensive, just whip out the old butane torch and smooth those prints with good old fashioned fire.

Continue reading “3D Print Finishing By Spraying Glazing Putty” →