Author: Jenny List

3060 Articles

A Decade Resistance Box From PCBs

March 13, 2025 by 19 Comments

One of those useful things to have around on your bench is a decade resistance box, essentially a dial-a-resistance instrument. They used to be quite expensive in line with the cost of close-tolerance resistors, but the prices have come down and it’s within reach to build your own. Electronic design consultancy Dekimo have a nice design for one made from a series of PCBs which they normally give out at trade fairs, but now they’ve released the files for download.

It’s released as Gerbers and BOM with a pick-and-place file only, and there’s no licence so it’s free-as-in-beer [Editor’s note: the license has been updated to CC-BY-SA], but that should be enough if you fancy a go. Our Gerber viewer is playing up so we’re not entirely sure how reliable using PCBs as wafer switches will be long-term, but since the pictures are all ENIG boards we’d guess the gold plating will be much better than the HASL on all those cheap multimeters.

We like this as a conference giveaway, being used to badges it’s refreshing to see a passive take on a PCB artwork. Meanwhile this isn’t the first resistance box we’ve seen with unconventional switches.

Lies, Damned Lies, And IGBT Datasheets

March 11, 2025 by 46 Comments

We have all seen optimistic claims for electronic products that fail to match the reality, and [Electronic Wizard] is following one up in a recent video. Can a relatively small IGBT really switch 200 A as claimed by a dubious seller? Off to the datasheet to find out!

The device in question is from Toshiba, and comes in a TO-220 package. This itself makes us pause for a minute, because we suspect the pins on a TO220 would act more like fuses at a steady 200 A.

But in the datasheet, there it is: 200 A. Which would be great, but of course it turns out that this is the instantaneous maximum current for a few microsecond pulse. Even then it’s not finished, because while the continuous current is supposed to he half that, in the datasheet it specifies a junction temperature of 25 °C. The cooling rig required to maintain that with this transistor passing 200 A would we think be a sight to behold, so for all intents and purposes this can’t even switch a continuous 100 A. And the real figure is much less as you’d imagine, but it raises an important point. We blindly read datasheets and trust them, but sometimes we should engage brain before releasing the magic smoke.

Continue reading “Lies, Damned Lies, And IGBT Datasheets” →

A Magic Eye Tube Does All The Work In This Kit

March 11, 2025 by 16 Comments

We’re used to low cost parts and a diversity of electronic functions to choose from in our projects, to the extent that our antecedents would be green with envy. Back when tubes were king, electronics was a much more expensive pursuit with new parts, so designers had to be much more clever in their work. [Thomas Scherrer OZ2CPU] has just such a design on his bench, it’s a Heathkit Capaci-Tester designed in 1959, and we love it for the clever tricks it uses.

It’s typical of Heathkits of this era, with a sturdy chassis and components mounted on tag strips. As the name suggests, it’s a capacitor tester, and it uses a magic eye tube as its display. It’s looking for short circuits, open circuits, and low equivalent resistance, and it achieves this by looking at the loading the device under test places on a 19 MHz oscillator. But here comes that economy of parts; there’s no rectifier so the circuit runs on an AC HT voltage from a transformer, and that magic eye tube performs the task of oscillator as well as display.

He finds it to be in good condition in the video below the break, though he removes a capacitor placed from one of the mains input lines to chassis. It runs, and confirms his test capacitor is still good. It can’t measure the capacitance, but we’re guessing the resourceful engineer would also have constructed a bridge for that.

Continue reading “A Magic Eye Tube Does All The Work In This Kit” →

Satellite Imagery You Can Play With

March 10, 2025 by 6 Comments

Satellite imagery is in the news right now, but not all satellite constellations are the preserve of governments. Satellogic operates a series of CubeSats with Earth imaging payloads, and best of all, they maintain an open dataset. [Mark Litwintschik] takes us through using it.

Starting with a script to recover the locations of the satellites, he moves on to the data itself. It’s in a huge S3 bucket, for which parsing the metadata becomes a big data question rather than one of simple retrieval. After parsing he loads the resulting data into a database, from which he can then perform queries more easily. He uses Qatar as his example, and shows us the resulting imagery.

The dataset isn’t comprehensive, it’s obvious that the areas surveyed have been done at the behest of customers. But who knows, your part of the world might be one of the areas in the dataset, and now you have all the tools you need to explore. It certainly beats low-res weather satellite imagery.

Expensive Camera, Cheap 3D-Printed Lens

March 8, 2025 by 8 Comments

If you’re a photography enthusiast, you probably own quite a few cameras, but the chances are your “good” one will have interchangeable lenses. Once you’ve exhausted the possibilities of the kit lens, you can try different focal lengths and effects, but you’ll soon find out that good glass isn’t cheap. Can you solve this problem by making your own lenses? [Billt] has done just that.

Given some CAD skills, it’s possible to replicate the mount on an existing lens, but he takes a shortcut by using a readily available camera cap project. There are two lenses detailed in the video below the break; the first is a plastic lens from a disposable camera, while the second takes one from a Holga toy camera. The plastic lens is inserted mid-print, giving the colour aberrations and soft focus you’d expect, while the Holga lens is mounted on a slide for focusing. There may be some room for improvement there, but the result is a pair of fun lenses for experimentation for not much outlay. Given the number of broken older cameras out there, it should be relatively easy for anyone wanting to try this for themselves to have a go.

The video is below the break, but while you’re on this path, take a look at a previous project using disposable camera lenses. Or, consider printing an entire camera.

Continue reading “Expensive Camera, Cheap 3D-Printed Lens” →

Open Source Hardware, How Open Do You Want It To Be?

March 7, 2025 by 43 Comments

In our wider community we are all familiar with the idea of open source software. Many of us run it as our everyday tools, a lot of us release our work under an open source licence, and we have a pretty good idea of the merits of one such document over another. A piece of open source software has all of its code released under a permissive licence that explicitly allows it to be freely reproduced and modified, and though some people with longer beards take it a little too seriously at times and different flavours of open source work under slightly different rules, by and large we’re all happy with that.

When it comes to open hardware though, is it so clear cut?  I’ve had more than one rant from my friends over the years about pieces of hardware which claim to be open-source but aren’t really, that I think this bears some discussion.

Open Source Hardware As It Should Be Done

To explore this, we’ll need to consider a couple of open source hardware projects, and I’ll start close to home with one of my own. My Single 8 home movie cartridge is a 3D printable film cartridge for a defunct format, and I’ve put everything necessary to create one yourself in a GitHub repository under the CERN OHL. If you download the file and load it into OpenSCAD you can quickly create an STL file for your slicer, or fiddle with the code and make an entirely new object. Open source at its most efficient, and everyone’s happy. I’ve even generated STLs ready to go for each of the supported ISO values. Continue reading “Open Source Hardware, How Open Do You Want It To Be?” →

Open Safety In The Auto Business: Renault Shares Its Battery Fire Suppression Tech

March 7, 2025 by 31 Comments

As consumers worldwide slowly make the switch from internal combustion vehicles to lower-carbon equivalents, a few concerns have appeared about electric vehicles. Range anxiety is ebbing away as batteries become bigger and chargers become more frequent, but a few well-publicized incidents have raised worries over fire safety.

Lithium-ion batteries can ignite in the wrong circumstances, and when they do so they are extremely difficult to extinguish. Renault has a solution, and in a rare moment for the car industry, they are sharing it freely for all manufacturers to use.

The innovation in question is their Fireman Access Port, a standardized means for a fire crew to connect up their hoses directly to the battery pack and attack the fire at its source. An opening is covered by an adhesive disk designed to protect the cells, but breaks under a jet of high-pressure water. Thermal runaway can then be halted much more easily.

The licensing terms not only allow use of the access port itself, but also require any enhancements be shared with the rest of the community of automakers using the system. This was the part which caught our interest, because even if it doesn’t come from the same place as the licences we’re used to, it sounds a lot like open source to us.

Oddly, this is not the first time Renault have open-sourced their technology, in the past they’ve shared an entire car.