In an age where our gadgets allow us to explore the cosmos, we stumbled upon sounds from a future past: an article on historical signals from Mars. The piece, written by [Paul Gilster] of Centauri Dreams, cites a Times essay published by [Becky Ferreira] of August 20. [Ferreira]’s essay sheds light on a fascinating, if peculiar, chapter in the history of the search for extraterrestrial life.
She recounts an event from August 1924 when the U.S. Navy imposed a nationwide radio silence for five minutes each hour to allow observatories to listen for signals from Mars. This initiative aimed to capitalize on the planet’s close alignment with Earth, sparking intrigue and excitement among astronomers and enthusiasts alike.
Here’s a question for you: when your PCB has a ground plane layer, where do return signals flow? It seems like a trick question, but as [Kristof Mulier] explains, there’s more to return path routing (alternate link in case you run into a paywall) than just doing a copper pour and calling it a day.
Like so many other things in life, the answer to the above question is “it depends,” and as [Kristof] ably demonstrates in this concise article, the return path for a signal largely depends on its frequency. He begins by explaining current loop areas and how they factor into the tendency for a circuit to both emit and be susceptible to electromagnetic noise. The bigger the loop area, the worse things can get from a noise perspective. At low frequencies, return signals will tend to take the shortest possible path, which can result in large current loop areas if you’re not careful. At higher frequencies, though, signals will tend to follow the path of minimal energy instead, which generally ends up being similar to the signal trace, even if it has a huge ground plane to flow through.
Since high-frequency signals naturally follow a path through the ground plane that minimizes the current loop, that means the problem takes care of itself, right? It would, except that we have a habit of putting all kinds of gaps in the way, from ground plane vias to isolation slots. [Kristof] argues that this can result in return paths that wiggle around these features, increasing the current loop area to the point where problems creep in. His solution? Route all your signal return paths. Even if you know that the return traces are going to get incorporated into a pour, the act of intentionally routing them will help minimize the current loop area. It’s brilliantly counterintuitive.
This is the first time we’ve seen the topic of high-frequency return paths tackled. This succinct demonstration shows exactly how return path obstructions can cause unexpected results.
Grounding of electrical systems is an often forgotten yet important design consideration. Issues with proper grounding can be complicated, confusing, and downright frustrating to solve. So much so that engineers can spend their entire careers specializing in grounding and bonding. [Bsilvereagle] was running into just this sort of frustrating problem while attempting to send audio from a Nintendo Switch into a PC, and documented some of the ways he attempted to fix a common problem known as a ground loop.
Ground loops occur when there are multiple paths to ground, especially in wires carrying signals. The low impedance path creates oscillations and ringing which is especially problematic for audio. When sending the Switch audio into a computer a loop like this formed. [Bsilvereagle] set about solving the issue using an isolating transformer. It took a few revisions, but eventually they settled on a circuit which improved sound quality tremendously. With that out of the way, the task of mixing the Switch audio with sources from other devices could finally proceed unimpeded.
As an investigation into a nuisance problem, this project goes into quite a bit of depth about ground loops and carrying signals over various transforming devices. It’s a great read if you’ve ever been stumped by a mysterious noise in a project. If you’ve never heard of a ground loop before, take a look at this guide to we featured a few years ago.
The demonstration is simple, using an ESP32 microcontroller fitted with two push buttons. When one button is pushed, it increments a counter and sends a Signal message noting the current count. The other button sends an image as a Signal message.
The project relies on a Signal bot to deliver an API key that enables the project to work. Messages are sent by making HTTP requests with this key to the CallMeBot.com server. With the API key as authentication, users can only send messages to their own number, keeping the system safe from spammers.
While the demonstration is basic, it merely serves to illustrate how the project works. The aim was to allow home automation and other Internet of Things systems to send Signal messages, and through this method, it’s now possible. The highly security conscious likely won’t want to rely on a random third party server, but for those tinkering around, it may not be such a big deal.
If you’ve been on the RTL-SDR forums lately you may have seen that a lot of work has been going into the DragonOS software. This is a software-defined radio group that has seen a lot of effort put into a purpose-built Debian-based Linux distribution that can do a lot of SDR out of the box. The latest and most exciting project coming from them involves a method for using the software to receive and demodulate analog video.
[Aaron]’s video (linked below) demonstrates using a particular piece of software called SigDigger to analyze an incoming analog video stream from a drone using a HackRF. (Of course any incoming analog signal could be used, it doesn’t need to be a drone.) The software shows the various active frequency ranges, allows a user to narrow in on one and then start demodulating it. While it has to be dialed in just right to get anything that doesn’t look like snow, [Aaron] is able to get recognizable results in just a few minutes.
Getting something like this to work completely in software is an impressive feat, especially considering that all of the software used here is free. Granted, this wouldn’t be as easy for a digital signal like most TV stations broadcast, but there’s still a lot of fun to be had. In case you missed the release of DragonOS, we covered it a few weeks ago and it’s only gotten better since then, with this project just as one example.
An ideal application for mesh networking is off-grid communication; when there’s no cellular reception and WiFi won’t reach, wide-area technologies like LoRa can be used to create ad hoc wireless networks. Whether you’re enjoying the outdoors with friends or conducting a rescue operation, a cheap and small gadget that will allow you to create such a network and communicate over it would be a very welcome addition to your pack.
That’s exactly the goal of the Meshtastic project, which aims to take off-the-shelf ESP32 LoRa development boards and turn them into affordable mesh network communicators. All you need to do is buy one of the supported boards, install the firmware, and starting meshing. An Android application that will allow you to use the mesh network to send basic text messages is now available as an alpha release, and eventually you’ll be able to run Signal over the LoRa link.
Navigating to another node in the network.
Developer [Kevin Hester] tells us that these are still the very early days, and there’s plenty of work yet to be done. In fact, he’s actively looking to bring a few like-minded individuals onto the project. So if you have experience with the ESP32 or mobile application development, and conducting private communications over long-range wireless networks sounds like your kind of party, this might be your lucky day.
From a user’s perspective, this project is extremely approachable. You don’t need to put any custom hardware together, outside of perhaps 3D printing a case for your particular board. The first time around you’ll need to flash the firmware with esptool.py, but after that, [Kevin] says future updates can be handled by the smartphone application.
Incidentally, the primary difference between the two boards is that the larger and more expensive one includes GPS. The mesh networking side of things will work with either board, but if everyone in your group has the GPS-equipped version, each user will be able to see the position of everyone else in the network.
It is easy to think that a Linux shell like Bash is just a way to enter commands at a terminal. But, in fact, it is also a powerful programming language as we’ve seen from projects ranging from web servers to simple utilities to make dangerous commands safer. Like most programming languages, though, there are multiple layers of complexity. You can spend a little time and get by or you can invest more time and learn about the language and, hopefully, write more robust programs.
