A Decade Resistance Box From PCBs

March 13, 2025 by Jenny List 18 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, 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.

I2C Sniffing Comes To The Bus Pirate 5

March 12, 2025 by Tom Nardi 6 Comments

While the Bus Pirate 5 is an impressive piece of hardware, the software is arguably where the project really shines. Creator [Ian Lesnet] and several members of the community are constantly working to add new features and capabilities to the hardware hacking multi-tool, to the point that if your firmware is more than a few days old there’s an excellent chance there’s a fresher build available for you to try out.

One of the biggest additions from the last week or so of development has been the I2C sniffer — a valuable tool for troubleshooting or reverse engineering devices using the popular communications protocol. [Ian] has posted a brief demo video of it in action.

It’s actually a capability that was available in the “classic” versions of the Bus Pirate, but rather than porting the feature over from the old firmware, [Ian] decided to fold the MIT licensed pico_i2c_sniffer from [Juan Schiavoni] into the new codebase. Thanks to the RP2040’s PIO, the sniffer works at up to 500 kHz, significantly outperforming its predecessor.

Admittedly, I2C sniffing isn’t anything you couldn’t do with a cheap logic analyzer. But that means dealing with captures and making sure the protocol decoder is setup properly, among other bits of software tedium. In comparison, once you start the sniffer program on the Bus Pirate 5, I2C data will be dumped out to the terminal in real-time for as long as you care to see it. For reverse engineering, it’s also very easy to move quickly from sniffing I2C packets to replaying or modifying them within the Bus Pirate’s interface.

If you already have a Bus Pirate 5, all you need to do is flash the latest firmware from the automated build system, and get sniffing. On the fence about picking one up? Perhaps our hands-on review will help change your mind.

A Magic Eye Tube Does All The Work In This Kit

March 11, 2025 by Jenny List 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.

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Hacking Digital Calipers For Automated Measurements And Sorta-Micron Accuracy

March 6, 2025 by Dan Maloney 14 Comments

We’ll take a guess that most readers have a set of digital calipers somewhere close to hand right now. The cheapest ones tend to be a little unsatisfying in the hand, a bit crusty and crunchy to use. But as [Matthias Wandel] shows us, these budget tools are quite hackable and a lot more precise than they appear to be.

[Matthias] is perhaps best known around these parts for making machine tools using mainly wood. It’s an unconventional material for things like the CNC router he loves to hate, but he makes it work through a combination of clever engineering and a willingness to work within the limits of the machine. To assess those limits, he connected some cheap digital calipers to a Raspberry Pi by hacking the serial interface that seems to be built into all of these tools. His particular calipers output a pair of 24-bit words over a synchronous serial connection a couple of times per second, but at a level too low to be read by the Pi. He solved this with a clever resistor ladder to shift the signals to straddle the 1.8 volt transition on the Pi, and after solving some noise problems with a few strategically placed capacitors and some software debouncing, he was gathering data on his Pi.

Although his setup was fine for the measurements he needed to make, [Matthias] couldn’t help falling down the rabbit hole of trying to milk better resolution from the calipers. On paper, the 24-bit output should provide micron-ish resolution, but sadly, the readings seem to fluctuate rapidly between two levels, making it difficult to obtain an average quickly enough to be useful. Still, it’s a good exercise, and overall, these hacks should prove handy for anyone who wants to dip a toe into automated metrology on a budget.

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Piggyback Board Brings Touch Sensing To USB Soldering Iron

March 5, 2025 by Dan Maloney 20 Comments

The current generation of USB-powered soldering irons have a lot going for them, chief among them being portability and automatic start and stop. But an iron that turns off in the middle of soldering a joint is a problem, one that this capacitive-touch replacement control module aims to fix.

The iron in question is an SJ1 from Awgem, which [DoganM95] picked up on Ali Express. It seems well-built, with a sturdy aluminum handle, a nice OLED display, and fast heat-up and cool-down. The problem is that the iron is triggered by motion, so if you leave it still for more than a second or two, such as when you’re soldering a big joint, it turns itself off. To fix that,[DoganM95] designed a piggyback board for the OEM controller with a TTP223 capacitive touch sensor. The board is carefully shaped to allow clearance for the existing PCB components and the heater cartridge terminals, and has castellated connections so it can connect to pads on the main board. You have to remove one MOSFET from the main board, but that’s about it for modifications. A nickel strip makes contact with the inside of the iron’s shell, turning it into the sensor plate for the TTP223.

[DoganM95] says that the BA6 variant of the chip is the one you want, as others have a 10-second timeout, which would defeat the purpose of the mod. It’s a very nice bit of design work, and we especially like how the mod board nests so nicely onto the OEM controller. It reminds us a little of those Quansheng handy-talkie all-band mods.

Inexpensive Powder Coating

March 4, 2025 by Al Williams 17 Comments

[Pete] had a friend who would powder coat metal parts for him, but when he needed 16 metal parts coated, he decided he needed to develop a way to do it himself. Some research turned up the fluid bed method and he decided to go that route. He 3D printed a holder and you can see how it all turned out in the video below.

A coffee filter holds the powder in place. The powder is “fluidized” by airflow, which, in this case, comes from an aquarium pump. The first few designs didn’t work out well. Eventually, though, he had a successful fluid bed. You preheat the part so the powder will stick and then, as usual, bake the part in an oven to cure the powder. You can expect to spend some time getting everything just right. [Pete] had to divert airflow and adjust the flow rate to get everything to work right.

With conventional powder coating, you usually charge the piece you want to coat, but that’s not necessary here. You could try a few other things as suggested in the video comments: some suggested ditching the coffee filter, while others think agitating the powder would make a difference. Let us know what you find out.

This seems neater than the powder coating guns we’ve seen. Of course, these wheels had a great shape for powder coating, but sometimes it is more challenging.

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A man in black glasses and a black t-shirt has his arms resting on a grey workbench. Between his opened hands are the two halves of a copper ice press. They are fist-sized copper cylinders. The lower half has large spiraling grooves to aid in the release of excess water from the ice being formed as it melts.

Make Ice Spheres In A Copper Press

March 2, 2025 by Navarre Bartz 11 Comments

Perfectly clear ice spheres are nifty but can be a bit tricky to make without an apparatus. [Seth Robinson] crafted a copper ice press to make his own.

Copper is well-known for its thermal conductivity, making it a perfect material for building a press to melt ice into a given shape. Like many projects, a combination of techniques yields the best result, and in this case we get to see 3d printing, sand casting, lost PLA casting, lathe turning, milling, and even some good old-fashioned sanding.

The most tedious part of the process appears to be dip coating of ceramic for the lost PLA mold, but the finished result is certainly worth it. That’s not to say that any of the process looks easy if you are a metal working novice. Taking over a week to slowly build up the layers feels a bit excruciating, especially compared to 3D printing the original plastic piece. If you’re ever feeling discouraged watching someone else’s awesome projects, you might want to stick around to the end when [Robinson] shows us his first ever casting. We’d say his skill has improved immensely over time.

If you’re looking for something else to do with casting copper alloys, be sure to checkout this bronze river table or [Robinson’s] copper levitation sphere.

Thanks to [DjBiohazard] for the tip!

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