A time domain reflectometer (TDR) is a useful tool to have for finding faults in a wiring harness. However, they don’t come cheap, putting them out of reach for many shadetree mechanics that like to work on their own cars. However, [László SZŐKE] has been exploring a neat way to build a similar device on the cheap.

Typically, time domain reflectometry involves shooting a short electric pulse down a wire, and listening for how long it takes to bounce back. The time depends on the length of the wire, so it can be used to determine the location of a break in conductivity. Unfortunately, these pulses move so fast that very fast, very expensive hardware is needed to make these measurements.

[László’s] technique relies on lower-tech hardware. Instead of sending a very short pulse down a wire, his rig uses a cheap C-Media USB audio device to send a 4 kHz or 8 kHz sine wave instead. Then, by listening to the reflection and measuring the phase shift, it’s possible to detect the distance to the end of the wire (or a break along its length). Some supporting hardware is required for protection’s sake, and to tune the setup for measuring shorter or longer cabling. However, with some smart software processing, [László] states that it’s possible to measure down to 1 cm resolution.

The idea is that this setup could prove particularly useful for automotive troubleshooting. If you measure a wire and the device reports a length of 30 cm, when you know the wire stretches several meters into the engine bay… you know there’s a break around 30 cm from your measurement point.

There’s still plenty of work to be done – for now, [László] is working on a new prototype that should have better performance when testing shorter cables. Still, we love to see this sort of out-of-the-box thinking put towards a common troubleshooting task. If you’re doing fun signal analysis work of your own, don’t hesitate to light up the tipsline.

Recently [Jeff Geerling] has been tinkering with FireWire in order to use some older gear, which includes the use of a Raspberry Pi HAT called the Firehat. This provides a 6-pin FireWire port courtesy of the VIA VT6315N PCIe-to-FireWire chipset. As is typical with USB gear today as well, some FireWire gear requires more power than a port can provide, requiring the use of a powered hub. Unfortunately the use of a powered FireWire hub caused a bit of a conflagration event on [Jeff]’s desk.

Part of the issue appears to be that this Firehat board was designed as a companion to the Equip-1 DV capture device, with no attention paid to the idea that someone might be backfeeding power from an attached hub. As a result the VIA chip cried uncle and let out the magic smoke.

With this Firehat board taking its name clearly a bit too literal, [Jeff] will be reporting his findings to the developers, in the hope that perhaps some diodes or another solution against backfeeding can be added to the final design. Fortunately he was sent this board for testing prior to public release, so this definitely shows a clear flaw that can now be corrected.

We hope that [Jeff] has a good HEPA air filtration setup in his office to get rid of the acrid magic smoke, as it’s not meant to be enjoyed for long periods.

Once the premium option for data transfers and remote control for high-end audiovisual and other devices, FireWire (IEEE 1394) has been dying a slow death ever since Apple and Sony switched over to USB. Recently Apple correspondingly dropped support for it in MacOS 26, and Linux will follow in 2029. The bright side of this when you’re someone like [Jeff Geerling] is that this means three more years of Linux support for one’s FireWire gear, including on the Raspberry Pi with prosumer gear from 1999.

If you’re not concerned about running the latest and greatest – and supported – software, then using an old or modern Mac or PC is of course an option, but with Linux support still available [Jeff] really wanted to get it working on Linux. Particularly on a Raspberry Pi in order to stay on brand.

Adding a FireWire port to a Raspberry Pi SBC is easy enough with an RPi 5 board as you can put a Mini PCIe HAT on it into which you slot a mini PCIe to Firewire adapter. At this point lspci shows the new device, but to use it you need to recompile the Linux kernel with Firewire support. On the Raspberry Pi you then also need to enable it in the device tree overlay, as shown in the article.

With this you now have FireWire 400 support right off the bat, but to use the FireWire 800 port you need to also connect external power to the adapter, which [Jeff]’s Canon GL1 video camera with its FW400 port does not require, so he didn’t bother with that.

Capturing the video from the GL1 via FW400 was done using the DVgrab utility, with a subsequent capture attempt successful. This means that at least until 2029 [Jeff] will be happily using his GL1 camera this way.

Meanwhile over on the Dark Side, you can still happily install FireWire drivers made for older Windows versions on Windows 10 and 11, which is great news for e.g. people who have expensive DAW gear kicking around. Perhaps the demise of FireWire is still a long while off as long as you’re not too picky about the OS you’re running.