A man's gloved hand is need adjusting the valve on a cylinder, from which a clear plastic tube extends. The man's other hand is seen holding the the other end of the tube in front of a dish of burning wax, which is flaring brightly.

Testing Laughing Gas For Rocket Propellant

January 7, 2026 by 17 Comments

Nitrous oxide’s high-speed abilities don’t end with racing cars, as it’s a powerful enough oxidizer to be a practical component of rocket propellant. Since [Markus Bindhammer] is building a hybrid rocket engine, in his most recent video he built and tested a convenient nitrous oxide dispenser.

The most commercially available form of nitrous oxide is as a propellant for whipped cream, for which it is sold as “cream chargers,” basically small cartridges of nitrous oxide which fit into cream dispensers. Each cartridge holds about eight grams of gas, or four liters at standard temperature and pressure. To use these, [Markus] bought a cream dispenser and disassembled it for the cartridge fittings, made an aluminium adapter from those fittings to a quarter-inch pipe, and installed a valve. As a quick test, he fitted a canister in, attached it to a hose, lit some paraffin firelighter, and directed a stream of nitrous oxide at it, upon which it burned much more brightly and aggressively.

It’s not its most well-known attribute in popular culture, but nitrous oxide’s oxidizing potential is behind most of its use by hackers, whether in racing or in rocketry. [Markus] is no stranger to working with nitrogen oxides, including the much more aggressively oxidizing nitrogen dioxide.

Continue reading “Testing Laughing Gas For Rocket Propellant” →

How Do PAL And NTSC Really Work?

January 7, 2026 by 37 Comments

Many projects on these pages do clever things with video. Whether it’s digital or analogue, it’s certain our community can push a humble microcontroller to the limit of its capability. But sometimes the terminology is a little casually applied, and in particular with video there’s an obvious example. We say “PAL”, or “NTSC” to refer to any composite video signal, and perhaps it’s time to delve beyond that into the colour systems those letters convey.

Know Your Sub-carriers From Your Sync Pulses

A close-up on a single line of composite video from a Raspberry Pi.
A close-up on a single line of composite video from a Raspberry Pi.

A video system of the type we’re used to is dot-sequential. It splits an image into pixels and transmits them sequentially, pixel by pixel and line by line. This is the same for an analogue video system as it is for many digital bitmap formats. In the case of a fully analogue TV system there is no individual pixel counting, instead the camera scans across each line in a continuous movement to generate an analogue waveform representing the intensity of light. If you add in a synchronisation pulse at the end of each line and another at the end of each frame you have a video signal.

But crucially it’s not a composite video signal, because it contains only luminance information. It’s a black-and-white image. The first broadcast TV systems as for example the British 405 line and American 525 line systems worked in exactly this way, with the addition of a separate carrier for their accompanying sound. Continue reading “How Do PAL And NTSC Really Work?” →

A photo of the various parts for this MSLA 3D printer

Build A 2K Resolution MSLA 3D Resin Printer For Cheap

January 7, 2026 by 13 Comments

Have an old Android device collecting dust somewhere that you’d like to put to better use? [Electronoobs] shows us how to make a Masked Stereolithography Apparatus (MSLA) printer for cheap using screens salvaged from old Android phones or tablets.

[Electronoobs] wanted to revisit his earlier printer with all the benefits of hindsight, and this is the result. The tricky bit, which is covered in depth in the video below the break, is slicing up the model into graphics for each layer, so that these layers can be rendered by the LCD for each layer during the print.

The next tricky bit, once your layer graphics are in hand, is getting them to the device. This build does that by installing a custom Android app which connects to a web app hosted on the ESP32 microcontroller controlling the print, and the app has a backchannel via a USB OTG adapter installed in the device. [Electronoobs] notes that there are different and potentially better ways by which this full-duplex communication can be achieved, but he is happy to have something that works.

If you’re interested in resin printer tech, be sure to check out Continuous Printing On LCD Resin Printer: No More Wasted Time On Peeling? Is It Possible? and Resin Printer Temperature Mods And Continuous IPA Filtration.

The Rise And Fall Of The In-Car Fax Machines

January 7, 2026 by 49 Comments

Once upon a time, a car phone was a great way to signal to the world that you were better than everybody else. It was a clear sign that you had money to burn, and implied that other people might actually consider it valuable to talk to you from time to time.

There was, however, a way to look even more important than the boastful car phone user. You just had to rock up to the parking lot with your very own in-car fax machine.

Continue reading “The Rise And Fall Of The In-Car Fax Machines” →

An RP2040 Powered ADS-B Receiver

January 7, 2026 by 34 Comments

If you’ve ever heard the sound of an aircraft passing overhead and looked at an online plane tracker to try and figure out what it was, then you’ve interacted with ADS-B. It’s a protocol designed to enable easier aircraft monitoring, and it just so happens you can decode it yourself with the right hardware and software — which is how [John McNelly] came to develop ADSBee, an open source ADS-B receiver based around an RP2040.

ADS-B uses on–off keying (OOK) at 1 Mbps, and operates at 1090 MHz. This might seem like a rather difficult protocol to decode on a microcontroller, but the RP2040’s PIO is up to the task. All it takes is a bit of optimization, and a some basic RF components to amplify and digitize the signals.

However, not all aircraft utilize the 1090 MHz ADS-B implementation, and instead use a related protocol called UAT. Operating at 978 MHz, a second receiver is needed for decoding UAT traffic data, which is where the CC1312 comes into play. ADSBee may even be the first open source implementation of a UAT decoder!

What’s quite impressive is the various form factors the module is available in. Ranging from small solder-down modules to weatherproof outdoor base stations, nearly every potential need for an ADS-B receiver is covered. With POE or ESP32 S3 options available, there is no shortage of networking options either!

ADSBees have been placed in numerous locations, ranging from base stations to drones. One user even built out a tiny flight display cluster complete with traffic indicators into an FPV drone.

This isn’t the first time we have seen ADS-B receivers used by drone enthusiasts, but this is certainly the most feature rich and complete receiver we have come across.

Repairing A Self-Destructing SRS DG535 Digital Delay Generator

January 7, 2026 by No comments

There’s a lot of laboratory equipment out there that the casual hobbyist will never need to use, but that doesn’t mean you wouldn’t snap it up if the price is right. That’s what happened when [Tom Verbeure] saw a 1980s digital delay generator at a flea market for $40. Not only is it an excellent way to learn something about these devices, but it also provides a fascinating opportunity to troubleshoot and hopefully fix it. Such was also the case with this Stanford Research Systems (SRS) DG535 that turned out to be not only broken, but even features an apparently previously triggered self-destruct feature.

These devices are pretty basic, with this specimen incorporating a Z80 MPU in addition to digital and analog components to provide a programmable delay with 12.5 nanosecond resolution on its output channels after the input trigger is sensed. For that reason it was little surprise that the problem with the device was with its supply rails, of which a few were dead or out of spec, along with a burned-out trace.

Where the self-destruct feature comes into play is with the use of current boosting resistors around its linear regulators. Although these provide a current boost over what the regulator can provide, their disadvantages include a tendency towards destruction whenever the load on the supply rail decreases. This could for example occur when you’re debugging an issue and leave some of the PCBs disconnected.

Unsurprisingly, this issue caused the same charred trace to reignite during [Tom]’s first repair attempt, but after working up the courage over the subsequent 18 months the second repair attempt went much better, also helped by the presence of the mostly correct original board schematics.

Ultimately the fixes were relatively modest, involving replacing a discrete diode bridge with an integrated one, fixing the -9 V rail with a bodge wire, and replacing the LCD with its busted AC-powered backlight with a modern one with a LED backlight. Fortunately running the 5 V rail at 7 V for a while seemed to have caused no readily observable damage, nor did flipping connectors because of SRS’ inconsistent ‘standards’ for its connector orientations.

Sadly, when [Tom] emailed SRS to inquire about obtaining an updated schematic for this unit — which is currently still being sold new for $4,495 — he merely got told to send his unit in for repair.

Ken Shirriff working on the Commodore PET

This 8-Bit Commodore PET Was Hard To Fix

January 6, 2026 by 13 Comments

Over on [Ken Shirriff]’s blog is a tricky Commodore PET repair: tracking down 6 1/2 bad chips. WARNING: contains 8-bit assembly code.

The Trinity of 1977 which started the personal computer revolution were the Apple II, the Commodore PET, and the TRS-80. In this project it’s a failing Commodore PET which is being restored.

Continue reading “This 8-Bit Commodore PET Was Hard To Fix” →