Author: Jenny List

3281 Articles

DIY All-Transistor Addressable Pixel

February 26, 2021 by 36 Comments

By now most readers should be used to addressable LEDs, devices that when strung out in a connected chain can be individually lit or extinguished by a serial data stream. Should you peer at one under a microscope you’ll see alongside the LED dies an integrated circuit that handles all the address decoding. It’s likely to be quite a complex device, but how simply can its functions be replicated? It’s a theme [Tim] has explored in the TransistorPixel, and addressable LED board that achieves addressability with only 17 transistors.

It uses a surprisingly straightforward protocol, in which a pulse longer than 500ns enables the LED while a shorter one turns it off. Subsequent pulses in a train are passed on down the line to the next device. A 20µs absence of a pulse resets the string and sets it to wait for the next pulse train. Unlike the commercial addressable LEDS there is only a single colour and no suport for gradated brightness, but it’s still an impressive circuit.

Under the hood is some very old-school RTL logic, a monostable to detect the pulse and a selection of gates and a latch to capture the state and forward to the chain. It’s laid out on a PCB in order of circuit function, and while we can see that maybe it’s not a practical addresssable LED for 2021, it’s likely that it could be made into a much smaller PCB if desired.

Perhaps unsurprisingly given the ready availability of addressable LEDs, we’ve not seen many home made ones. This addressable 7-segment display may be the closest.

May (No Longer) Contain Hackers: MCH 2021 Has Been Cancelled

February 25, 2021 by 7 Comments

In a sad but unsurprising turn of events, MCH, this summer’s large hacker camp in the Netherlands, has been cancelled. Organising a large event in a pandemic would inevitably carry some risk, and despite optimism that the European vaccine strategy might have delivered a safe environment by the summer that risk was evidently too high for the event organisers IFCAT to take on. Our community’s events come from within the community itself rather than from commercial promoters, and the financial liability of committing to hire the site and infrastructure would have been too high to bear had the event succumbed to the pandemic. Tickets already purchased will be refunded, and they leave us with a crumb of solace by promising that alternatives will be considered. We understand their decision, and thank them for trying.

As with all such events the behind-the-scenes work for MCH has already started. The badge has been revealed in prototype form, the call for participation has been completed, and the various other event team planning will no doubt be well  under way. This work is unlikely to be wasted, and we hope that it will bear fruit at the next Dutch event whenever that may be.

It would have been nice to think that by now we could be seeing the light at the end of the pandemic tunnel, but despite the sterling work of scientists, healthcare workers, and epidemiologists, it seems we still have a a way to go before we’ll once more be hanging out together drinking Club-Mate in the company of thousands of others. If the pandemic is weighing upon you, take care of yourselves.

Turn An Ender 3 Into A Belt 3D Printer Of Your Very Own

February 25, 2021 by 20 Comments

Infinite-bed 3D printers have long been an object of desire in our community, but it has taken a long time for the promise to catch up with the reality in terms of relatively affordable models that live up to expectations. They’re still a little expensive compared to their fixed-bed cousins though, so if you hanker for a Creality CR30 but only have the cash for an Ender 3, [Michael Sgroi] may have the project for you. He’s created the EnderLoop, a set of parts to perform the conversion from a stock Ender 3 to a fully-functional belt printer.

It takes the Ender 3 gantry and tilts it sideways on a pair of 3D printed supports, and replaces the stock Y azis with a belt on rollers driven by a larger motor through a timing belt drive. He has a variety of suggestions for sourcing a belt, and in his case he’s chosen one from PowerBelt3D. As well as the GitHub repository already linked, it can also be found on Thingiverse.

It’s clear that hacking apart a reliable printer in this way is not for the faint-hearted, and that a cautious hacker might prefer to wait a while for a cheaper off-the-shelf model. But we can see that the reliability of the Ender 3 will mean that its parts are still of decent quality in the new configuration, and that it looks as though the base printer can be reassembled should a belt-based build be a failure. Infinite bed printers will inevitably have a major presence in our community, and it is designs such as this one which will lead the way as they evolve into reliable machines.

Taking A Capacitor Microphone To The Next Level

February 24, 2021 by 13 Comments

There was a time when a microphone for most people was a cheap plastic affair that probably came for free with their sound card, but in the age of pandemic video streaming no desktop is complete without a chunky model that looks for all the world as though it escaped from a studio. Few people make their own microphones, so the work of [DJJules] in building very high quality condenser microphones is a particularly fascinating read.

A condenser microphone is a capacitor in which one plate is formed by a conductive diaphragm. A bias voltage is supplied to the diaphragm via a resistor, and since the charge on the plate remains constant as its capacitance changes with the sound vibrations, the voltage on the capacitor changes accordingly. This is picked up by a high impedance buffer and from there fed to a normal microphone input. This Instructable uses a commercial condenser microphone capsule, and takes the reader through generating the bias voltage for it before describing the op-amp buffer circuit.

The most interesting part comes at the end, as we’re shown how the sensitivity pattern of a dual-microphone array can be tuned to be omnidirectional, cardoid, or figure-of-eight. This is probably the norm among audio engineers, but we rarely see this sort of insight in our community. We may never build a microphone of our own, but it’s fascinating to see this one from the ground up in the video below the break.

If you’re confused about the difference between a condenser microphone and the more common electret condenser microphone, we have published a guide to that topic. Continue reading “Taking A Capacitor Microphone To The Next Level” →

Mastering The Tricky Job Of Soldering SMA Connectors

February 22, 2021 by 22 Comments

There’s a satisfaction in watching someone else at work, particularly when they are demonstrating a solution to a soldering problem you have encountered in the past. SMA panel sockets have a particularly tiny solder bucket on their reverse, and since they often need to be soldered onto brass rod as part of microwave antenna construction they present a soldering challenge. [Andrew McNeil] is here to help, with a foolproof method of achieving a joint that is both electrically and mechanically sound.

The best connections to a solder bucket come when the wire connected to it nestles within its circular center. If this doesn’t happen and a blob of solder merely encapsulates both wire and bucket, the mechanical strength of the solder blob alone is not usually sufficient. The brass rod is wider than the bucket, so he takes us through carefully grinding it down to the right diameter for the bucket so it sits in place and can have the solder sweated into the gap. The result is very quick and simple, but has that essential satisfaction we mentioned earlier. It’s a small hack, but if you’ve ever soldered to a too-small RF connector you’ll understand. For more fun and games with RF connectors, take a look at our overview.

Continue reading “Mastering The Tricky Job Of Soldering SMA Connectors” →

How Tiny Can A Microcontroller Dev Board Be!

February 21, 2021 by 12 Comments

With innumerable microcontroller boards on the market it’s sure that there will be one for every conceivable application or user. Among them are some seriously tiny ones, but this wasn’t enough for [Alun Morris]. Wanting to see how small he could make an ATtiny board without a custom PCB, he took a SOIC-8 version of the popular minimalist processor and mated it to a 6mm by 8mm piece of 0.05″ prototyping board to create a device that is dwarfed by its connectors.

It’s an extremely simple circuit and hardly something that hasn’t been done before, but the value here is in the tricky soldering to make it rather than its novelty. The ATtiny402 and three passive SMD components are fitted on the smallest possible sliver of prototyping board to contain them, and the female headers and set of programming pins contribute far more to the volume of the device than the board itself. He also tried a side-on design with two smaller slivers of board before settling on the more conventional layout. The demonstration of the system in action seen in the video below the break is a magnetic flux detector, dwarfed by the 40-pin DIP Z80 it is sitting on.

A lot of boards claim to be tiny, but few are this small. This ESP32 is a more usual contender.

Continue reading “How Tiny Can A Microcontroller Dev Board Be!” →

Volumetric 3D Television Is Here!

February 21, 2021 by 18 Comments

Volumetric 3D displays that allow the viewing of full 3D images without special glasses are not unknown in our community, usually taking the form of either a 3D LED matrix or a spinning rotor either with an image projected onto it or holding an LED array. They are impressive projects, but they are often limited in what they can display. Pretty patterns and simple 3D models are all very well, but they are hardly 3D television. Thus we’re quite impressed with [Evlmnkey]’s bachelor’s degree project, which combines motion capture and a volumetric display for a genuine volumetric 3D closed-circuit television system.

Finding the details takes a bit of dredging through the Reddit thread, but the display is an off-the-shelf Adafruit single-sided LED matrix driven by an ESP32, all mounted on a motor with a pair of slip rings for power. Data is fed to the ESP via WiFi, with the PC responsible for grabbing the image sending it as uncompressed frames. There’s little detail on the 3D capture, but since he mentions a Kinect library we suspect that may be the source.

This is perhaps not the highest resolution TV you’ll ever have seen, indeed we’d liken it to the flickering 30 lines of 1930s mechanical TV, but it’s still a functioning volumetric 3D live CCTV system. If you’re interested by 3D displays, you might like to see our examination of the subject.

Thanks [nandkeypull] for the tip.