Linux Fu: A Little Bit Of (Network) History Repeating Itself

These days, embedded systems often have networks and that can make them significantly more complex. Networks are usually pretty nondeterministic and there are a variety of oddball conditions. For example, when your public-access pick and place machine gets written up on Hackaday and you suddenly get a 50X surge in traffic, how does your network stack handle it? While there’s no silver bullet for network testing, there are some tricks that can make it easier and one of those is the tcpreplay utilities that allow you to record complex network traffic and then play it back in a variety of ways. This has many benefits, especially if you manage to capture that one thing that triggers bad behavior sporadically. Being able to play it back on demand can speed up diagnostics considerably.

General Idea

You probably know that tcpdump allows you to grab packet captures from a network interface and save them to a file. If you prefer a GUI, you probably use Wireshark, which uses the same underlying library (libpcap) to grab the data. In fact, you can capture data using tcpdump and look at it with Wireshark, although there are other tools like tcptrace or Ngrep that can work with the output, also.

While the output of the command can be a little cryptic without tool support, a program called tcpreplay can take that data and feed it back in a variety of ways. Of course, you can modify the file first — there are tools to make that easier and — if you need to — you can craft your own network traffic by hand or using one of a variety of tools. This process is often called “packet crafting.”

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Open Source Electric Vehicle Charging

Electric vehicles are becoming more and more common on the road, but when they’re parked in the driveway or garage there are still some kinks to work out when getting them charged up. Sure, there are plenty of charging stations on the market, but they all have different features, capabilities, and even ports, so to really make sure that full control is maintained over charging a car’s batteries it might be necessary to reach into the parts bin and pull out a trusty Arduino.

This project comes to us from [Sebastian] who needed this level of control over charging his Leaf, and who also has the skills to implement it from the large high voltage switching contactors to the software running its network connectivity and web app. This charging station has every available feature, too. It can tell the car to charge at different rates, and can restrict it to charging at different times (if energy is cheaper at night, for example). It is able to monitor the car’s charge state and other information over the communications bus to the vehicle, and even has a front-end web app for monitoring and controlling the device.

The project is based around an Arduino Nano 33 IoT with all of the code available on the project’s GitHub page. While we would advise using extreme caution when dealing with mains voltage and when interfacing with a high-ticket item like an EV, at first blush the build looks like it has crossed all its Ts and might even make a good prototype for a production unit in the future. If you don’t need all of the features that this charging station has, though, you can always hack the car itself to add some more advanced charging features.

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Raspberry Pi Tally Lights

Running a camera studio is a complicated affair from pretty much every angle. Not only is the camera gear expensive but the rest of the studio setup takes care and attention down to the lighting as well. When adding multiple cameras to the mix, like for a television studio, the level of complexity increases exponentially. It’s great to have a few things that simplify the experience of running all of this equipment too, without the solution itself causing more problems than it solves, like these network-operated Raspberry Pi-powered tally lights.

A tally light is the light on a camera that lets the person being recorded know which camera is currently in use. Networking them all together often requires complex wiring or at least some sort of networking solution, which is what this particular build uses. However, the lights are controlled directly over HTTP rather than using a separate application which might need a port open on a firewall or router, which not only simplifies their use but doesn’t decrease network security.

The HTTP interface, plus all of the software and schematics for this build, are available on the project’s GitHub page. We imagine the number of people operating a studio and who are in need of a tally light system to be fairly low, but the project is interesting from a networking point-of-view regardless of application. If you do have a studio like this and are looking for other ways to improve it, we do have a simple teleprompter hack that might be right up your alley.

True Networked KVM Without Breaking The Bank

For administering many computers at once, an IP KVM is an invaluable piece of equipment that makes it possible to get the job done over the network without having to haul a keyboard, monitor, and mouse around to each computer. The only downside is that they can get pricey, unless of course you can roll one out based on the Raspberry Pi and the PiKVM image for little more than the cost of the Pi itself.

The video linked below shows how to set all of this up, which involves flashing the image and then setting up the necessary hardware. The build shows an option for using HDMI over USB, but another option using the CSI bus would allow for control over options like video resolution and color that a USB HDMI dongle doesn’t allow for. It also makes it possible to restart the computer and do things like configure BIOS or boot from removable media, which is something that would be impossible with a remote desktop solution like VNC.

The creator of PiKVM was mentioned in a previous post about the creation of the CSI bus capture card, and a Pi hat based on this build will be available soon which would include options for ATX controls as well. Right now, though, it’s possible to build all of this on your own without the hat, and is part of what makes the Pi-KVM impressive, as well as its very low cost.

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Modern Network Adapter For Retro Computers

Universal Serial Bus, or USB, is so ingrained in modern computing that it’s hard to imagine a time without it. That time did exist, though, and it was a wild west of connector types, standards, and interfacing methods. One of the more interesting interfaces of the time was the SIO system found in 8-bit Atari computers which ended up sharing a lot of the features of modern USB, and its adaptability is displayed in this modern project which brings WiFi, Bluetooth, USB, and SD card slots to any old Atari with an SIO port.

The project is called FujiNet and it uses the lightweight protocol of SIO to add a number of modern features to the 8-bit machine. It’s based on an ESP32, and the chip performs the functions of a network adapter by bridging WiFi and Bluetooth to the Atari. It does this by simulating drives that would have potentially been used on the Atari in its time, such as a floppy disk drive, an RS232 interface, or a modem, and translating them to the modern wireless communication protocols. It even has the ability to emulate a printer by taking the output of the print job from the Atari and converting it to PDF within the device itself.

Not only does this bring a lot of functionality to the Atari, which you may be able to use to view sites like, but the FujiNet is housed in a period-appropriate 3D-printed case that matches the look and feel of the original Atari. If you need a more generic solution for your retrocomputing networking adventures that isn’t limited to SIO, we recommend grabbing a Raspberry Pi to handle that.

Thanks to [Gavin] for the tip!

Take Security Up A Notch By Adding LEDs

All computers are vulnerable to attacks by viruses or black hats, but there are lots of steps that can be taken to reduce risk. At the extreme end of the spectrum is having an “air-gapped” computer that doesn’t connect to a network at all, but this isn’t a guarantee that it won’t get attacked. Even transferring files to the computer with a USB drive can be risky under certain circumstances, but thanks to some LED lights that [Robert Fisk] has on his drive, this attack vector can at least be monitored.

Using a USB drive with a single LED that illuminates during a read OR write operation is fairly common, but since it’s possible to transfer malware unknowingly via USB drives, one that has a separate LED specifically for writing operations will help alert a user to any write operations that might be trying to fly under the radar. A recent article by [Bruce Schneier] pointed out this flaw in USB drives, and [Robert] was up to the challenge. His build returns more control to the user by showing them when their drive is accessed and in what way, which can also be used to discover unique quirks of one’s chosen operating system.

[Robert] is pretty familiar with USB drives and their ups and downs as well. A few years ago he built a USB firewall that was able to decrease the likelihood of BadUSB-type attacks. Be careful going down the rabbit hole of device security, though, or you will start seeing potential attacks hidden almost everywhere.

PoE Powers Christmas Lights, But Opens Up So Much More

Addressable LEDs are a staple of homemade Christmas decorations in our community, as is microprocessor control of those LEDs. So at first sight [Glen Akins]’ LED decorated Christmas tree looks pretty enough, but isn’t particularly unusual. But after reading his write-up you’ll discover there’s far more to the project than meets the eye, and learn a lot about the technologies behind it that has relevance far beyond a festive light show.

The decoration is powered exclusively from power-over-Ethernet, with a PIC microcontroller translating Art-Net DMX-over-Ethernet packets into commands for the LED string. The control board is designed from the ground up and includes all the PoE circuitry, and the write-upĀ  gives a very thorough introduction to this power source that takes the reader way beyond regarding PoE as simply another off-the-shelf black box. Along the way we see all his code, as well as learn a few interesting tidbits such as the use of a pre-programmed EEPROM containing a unique MAC address.

So if your house has CAT5 wiring and you want an extra dimension to your festive splendour, you’ve officially got a whole year to build your own version. He’s featured here before, with his buzzer to break the Caps Lock habit.

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