Author: Dan Maloney

3313 Articles

Double Your Analog Oscilloscope Fun With This Retro Beam Splitter

November 24, 2024 by 18 Comments

These days, oscilloscope hacking is all about enabling features that the manufacturer baked into the hardware but locked out in the firmware. Those hacks are cool, of course, but back in the days of analog scopes, unlocking new features required a decidedly more hardware-based approach.

For an example of this, take a look at this oscilloscope beam splitter by [Lockdown Electronics]. It’s a simple way to turn a single-channel scope into a dual-channel scope using what amounts to time-division multiplexing. A 555 timer is set up as an astable oscillator generating a 2.5-kHz square wave. That’s fed into the bases of a pair of transistors, one NPN and the other PNP. The collectors of each transistor are connected to the two input signals, each biased to either the positive or negative rail of the power supply. As the 555 swings back and forth it alternately applies each input signal to the output of the beam splitter, which goes to the scope. The result is two independent traces on the analog scope, like magic.

More after the break…

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RFID From First Principles And Saving A Cat

November 23, 2024 by 5 Comments

[Dale Cook] has cats, and as he readily admits, cats are jerks. We’d use stronger language than that, but either way it became a significant impediment to making progress with an RFID-based sensor to allow his cats access to their litterbox. Luckily, though, he was able to salvage the project enough to give a great talk on RFID from first principles and learn about a potentially tragic mistake.

If you don’t have 20 minutes to spare for the video below, the quick summary is that [Dale]’s cats are each chipped with an RFID tag using the FDX-B protocol. He figured he’d be able to build a scanner to open the door to their playpen litterbox, but alas, the read range on the chip and the aforementioned attitude problems foiled that plan. He kept plugging away, though, to better understand RFID and the electronics that make it work.

To that end, [Dale] rolled his own RFID reader pretty much from scratch. He used an Arduino to generate the 134.2-kHz clock signal for the FDX-B chips and to parse the returned data. In between, he built a push-pull driver for the antenna coil and an envelope detector to pull the modulated data off the carrier. He also added a low-pass filter and a comparator to clean up the signal into a nice square wave, which was fed into the Arduino to parse the Differential Manchester-encoded data.

Although he was able to read his cats’ chips with this setup, [Dale] admits it was a long road compared to just buying a Flipper Zero or visiting the vet. But it provided him a look under the covers of RFID, which is worth a lot all by itself. But more importantly, he also discovered that one cat had a chip that returned a code different than what was recorded in the national database. That could have resulted in heartache, and avoiding that is certainly worth the effort too.

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Close Shave For An Old Oscilloscope Saved With A Sticky Note

November 23, 2024 by 12 Comments

When you tear into an old piece of test equipment, you’re probably going to come up against some surprises. That’s especially true of high-precision gear like oscilloscopes from the time before ASICs and ADCs, which had to accomplish so much with discrete components and a lot of engineering ingenuity.

Unfortunately, though, those clever hacks that made everything work sometimes come back to bite you, as [Void Electronics] learned while bringing this classic Tektronix 466 scope back to life. A previous video revealed that the “Works fine, powers up” eBay listing for this scope wasn’t entirely accurate, as it was DOA. That ended up being a bad op-amp in the power supply, which was easily fixed. Once powered up, though, another, more insidious problem cropped up with the vertical attenuator, which failed with any setting divisible by two.

With this curious symptom in mind, [Void] got to work on the scope. Old analog Tek scopes like this use a bank of attenuator modules switched in and out of the signal path by a complex mechanical system of cams. It seemed like one of the modules, specifically the 4x attenuator, was the culprit. [Void] did the obvious first test and compared the module against the known good 4x module in the other channel of the dual-channel scope, but surprisingly, the module worked fine. That meant the problem had to be on the PCB that the module lives on. Close examination with the help of some magnification revealed the culprit — tin whiskers had formed, stretching out from a pad to chassis ground. The tiny metal threads were shorting the signal to ground whenever the 4x module was switched into the signal path. The solution? A quick flick with a sticky note to remove the whiskers!

This was a great fix and a fantastic lesson in looking past the obvious and being observant. It puts us in the mood for breaking out our old Tek scope and seeing what wonders — and challenges — it holds.

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Quick And Very Dirty Repair Gets Smoked PLC Back In The Game

November 21, 2024 by 11 Comments

When electronics release the Magic Smoke, more often than not it’s a fairly sedate event. Something overheats, the packaging gets hot enough to emit that characteristic and unmistakable odor, and wisps of smoke begin to waft up from the defunct component. Then again, sometimes the Magic Smoke is more like the Magic Plasma, as was the case in this absolutely smoked Omron programmable logic controller.

Normally, one tasked with repairing such a thing would just write the unit off and order a replacement. But [Defpom] needed to get the pump controlled by this PLC back online immediately, leading to the somewhat unorthodox repair in the video below. Whatever happened to this poor device happened rapidly and energetically, taking out two of the four relay-controlled outputs. [Defpom]’s initial inspection revealed that the screw terminals for one of the relays no longer existed, one relay enclosure was melted open, its neighbor was partially melted, and a large chunk of the PCB was missing. Cleaning up the damaged relays revealed what the “FR” in “FR4” stands for, as the fiberglass weave of the board was visible after the epoxy partly burned away before self-extinguishing.

With the damaged components removed and the dangerously conductive carbonized sections cut away, [Defpom] looked for ways to make a temporary repair. The PLC’s program was locked, making it impossible to reprogram it to use the unaffected outputs. Instead, he redirected the driver transistor for the missing relay two to the previously unused and still intact relay one, while adding an outboard DIN-mount relay to replace relay three. In theory, that should allow the system to work with its existing program and get the system back online.

Did it work? Sadly, we don’t know, as the video stops before we see the results. But we can’t see a reason for it not to work, at least temporarily while a new PLC is ordered. Of course, the other solution here could have been to replace the PLC with an Arduino, but this seems like the path of least resistance. Which, come to think of it, is probably what caused the damage in the first place.

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Simple Stack Of Ferrites Shows How Fluxgate Magnetometers Work

November 20, 2024 by 8 Comments

Have you ever wondered how a magnetometer works? We sure have, which was why we were happy to stumble upon this article on simple homebrew fluxgate magnetometers.

As [Maurycy] explains, clues to how a fluxgate magnetometer works can be found right in the name. We all know what happens when a current is applied to a coil of wire wrapped around an iron or ferrite core — it makes an electromagnet. Wrap another coil around the same core, and you’ve got a simple transformer.

Now, power the first coil, called the drive coil, with alternating current and measure the induced current on the second, or sense coil. Unexpected differences between the current in the drive coil and the sense coil are due to any external magnetic field. The difference indicates the strength of the field. Genius!

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Junk Box Build Helps Hams With SDR

November 20, 2024 by 5 Comments

SDRs have been a game changer for radio hobbyists, but for ham radio applications, they often need a little help. That’s especially true of SDR dongles, which don’t have a lot of selectivity in the HF bands. But they’re so darn cheap and fun to play with, what’s a ham to do?

[VK3YE] has an answer, in the form of this homebrew software-defined radio (SDR) helper. It’s got a few features that make using a dongle like the RTL-SDR on the HF bands a little easier and a bit more pleasant. Construction is dead simple and based on what was in the junk bin and includes a potentiometer for attenuating stronger signals, a high-pass filter to tamp down stronger medium-wave broadcast stations, and a series-tuned LC circuit for each of the HF bands to provide some needed selectivity. Everything is wired together ugly-style in a metal enclosure, with a little jiggering needed to isolate the variable capacitor from ground.

The last two-thirds of the video below shows the helper in use on everything from the 11-meter (CB) band down to the AM bands. This would be a great addition to any ham’s SDR toolkit.

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Hackaday Links: November 17, 2024

November 17, 2024 by 18 Comments

A couple of weeks back, we covered an interesting method for prototyping PCBs using a modified CNC mill to 3D print solder onto a blank FR4 substrate. The video showing this process generated a lot of interest and no fewer than 20 tips to the Hackaday tips line, which continued to come in dribs and drabs this week. In a world where low-cost, fast-turn PCB fabs exist, the amount of effort that went into this method makes little sense, and readers certainly made that known in the comments section. Given that the blokes who pulled this off are gearheads with no hobby electronics background, it kind of made their approach a little more understandable, but it still left a ton of practical questions about how they pulled it off. And now a new video from the aptly named Bad Obsession Motorsports attempts to explain what went on behind the scenes.

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