Nixie clock from a frequency counter

A Nixie Clock, The Hard Way

Notice: no vintage Hewlett Packard test equipment was harmed in the making of this overly complicated Nixie clock. In fact, if anything, the HP 5245L electronic counter came out better off than it went into the project.

HP 5245 hand-wired backplane
Beautiful hand-wired backplane in the HP 5245 counter.

We mention the fate of this instrument mainly because we’ve seen our fair share of cool-looking-old-thing-gutted-and-filled-with-Arduinos projects before, and while they can be interesting, there’s something deeply disturbing about losing another bit of our shared electronic heritage. To gut this device, which hails from the early 1960s and features some of the most beautiful point-to-point backplane wiring we’ve ever seen, would have been a tragedy, one that [Shahriar] wisely avoided.

After a bit of recapping and some power supply troubleshooting, the video below treats us to a tour of the Nixie-based beauty. It’s a wonderful piece, and still quite accurate after all these decades, although it did need a bit of calibration. Turning it into a clock non-destructively required adding a little bit of gear, though. Internally, [Shahriar] added a divide-by-ten card to allow the counter to use an external 10-MHz reference. Externally, an ERASynth++ programmable signal generator was used to send a signal to the counter from 0 Hz to 23,595.9 kHz, ramping up by 100 Hz every second.

The end result is the world’s most complicated 24-hour clock, which honestly wasn’t even the point of the build at all. It was to show off the glorious insides of the counter, introduce us to some cool new RF tools, and as always with [Shahriar]’s videos, to educate and inform. We’ve always enjoyed his wizardry, from his look into automotive radars to a million-dollar scope teardown, and this was another great project.

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This Frequency Generator Knows How To Get Down

What kind of clever things could you do with a signal that had a period of 2 hours? Or 20? Any ideas? No seriously, tell us. Because [Joseph Eoff] has come up with a way to produce incredibly low frequency signals that stretch out for hours, and we’d love to figure out what we can do with it.

To be fair, it’s not like [Joseph] has any ideas either. He thought it would be an interesting project, and figures now that he has the technology, maybe some application will come to him. They say that if you’ve got a hammer everything looks like a nail, so maybe the next project he sends our way will be a sinusoidal fish feeder.

[Joseph] says doing the software side of things with Pure Data wasn’t a problem, but getting it out of the computer proved to be tricky. It turns out that your average computer sound card isn’t equipped to handle frequencies down into the millihertz range (big surprise), so they need to be coaxed out with some extra hardware. Using a simple circuit not unlike an AM demodulator, he’s able to extract the low-frequency signal from a 16 kHz carrier.

So if you ever find yourself in need of a handful of hertz, now you’ve got the tool to generate them. At least it’s more practical than how they used to generate low frequency signals back in the 1900s.

3.2 GHz Vector Signal Generator Tear Down

[The Signal Path] snagged a fancy Rohde & Schwarz vector signal generator that can go up to 3.2 GHz, but sadly it wasn’t in working order. It powered up and even put out a 1 GHz signal, but the amplitude output was very wrong. Interestingly relative changes to the output were correct, it was just that the absolute output amplitude was off by quite a bit and changed with frequency. That started a detective job which you can follow along in the video below.

The instrument is pretty high-end, and did not report any problems even during self-check. This implied that all the internals were probably good and whatever was wrong probably lay close to the output. The service manual’s block diagram wasn’t terribly useful, especially given that all the processing portions appear to work well.

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Building A Pocket Sized Arduino Oscilloscope

There’s little question that an oscilloscope is pretty much a must-have piece of equipment for the electronics hacker. It’s a critical piece of gear for reverse engineering devices and protocols, and luckily for us they’re as cheap as they’ve ever been. Even a fairly feature rich four channel scope such as the Rigol DS1054Z only costs about as much as a mid-range smartphone. But if that’s still a little too rich for your taste, and you’re willing to skimp on the features a bit, you can get a functional digital oscilloscope for little more than pocket change.

While there are a number of very cheap pocket digital storage oscilloscopes (DSOs) on the market, [Peter Balch] decided he’d rather spin up his own version using off-the-shelf components. Not only was it an excuse to deep dive on some interesting engineering challenges, but it ended up bringing the price even lower than turn-key models. Consisting of little more than an Arduino Nano and a OLED display, the cost comes out to less than $10 USD for a decent DSO that’s about the size of a matchbox.

But not a great one. [Peter] is very upfront about the limitations of this DIY pocket scope: it can’t hit very high sample rates, and the display isn’t really big enough to convey anything more than the basics. But if you’re doing some quick and dirty diagnostics in the field, that might be all you need. Especially since there’s a good chance you can build the thing out of parts from the junk bin.

Even if you’re not looking to build your own version of the Arduino-powered scope [Peter] describes, his write-up is still full of fascinating details and theory. He explains how his software approach is to disable all interrupts, and put the microcontroller into a tight polling loop to read data from the ADC as quickly as possible. It took some experimentation to find the proper prescaler value for the Atmega’s 16MHz clock, but in the end found he could get a usable (if somewhat noisy) output with a 1uS sample rate.

Unfortunately, the Arduino’s ADC leaves something to be desired in terms of input range. But with the addition of an LM358 dual op-amp, the Arduino scope gains some amplification so it can pick up signals down into the mV range. For completion’s sake, [Peter] included some useful features in the device’s firmware, such as a frequency counter, square wave signal source, and even a voltmeter. With the addition of a 3D printed case, this little gadget could be very handy to have in your mobile tool kit.

If you’d rather go the commercial route, Hackaday’s very own [Jenny List] has been reviewing a number of very affordable models such as the DSO Nano 3 and the JYE Tech DSO150 build-it-yourself kit.

[Thanks to BaldPower for the tip.]

Fail Of The Week: How Not To Design An RF Signal Generator

We usually reserve the honor of Fail of the Week for one of us – someone laboring at the bench who just couldn’t get it together, or perhaps someone who came perilously close to winning a Darwin Award. We generally don’t highlight commercial products in FotW, but in the case of this substandard RF signal generator, we’ll make an exception.

We suppose the fail-badge could be pinned on [electronupdate] for this one in a way; after all, he did shell out $200 for the RF Explorer signal generator, which touts coverage from 24 MHz to 6 GHz. But in true lemons-to-lemonade fashion, the video below he provides us with a thorough analysis of the unit’s performance and a teardown of the unit.

The first step is a look at the signal with a spectrum analyzer, which was not encouraging. Were the unit generating a pure sine wave as it should, we wouldn’t see the forest of spikes indicating harmonics across the band. The oscilloscope isn’t much better; the waveform is closer to a square wave than a sine. Under the hood, he found a PIC microcontroller and a MAX2870 frequency synthesizer, but a conspicuous absence of any RF filtering components, which explains how the output got so crusty. Granted, $200 is not a lot to spend compared to what a lab-grade signal generator with such a wide frequency range would cost. And sure, external filters could help. But for $200, it seems reasonable to expect at least some filtering.

We applaud [electronupdate] for taking one for the team here and providing some valuable tips on RF design dos and don’ts. We’re used to seeing him do teardowns of components, like this peek inside surface-mount inductors, but we like thoughtful reviews like this too.

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Signal Generator Uses FPGA

Although there are a few exceptions, FPGAs are predominantly digital devices. However, many FPGA applications process analog data, so you often see an FPGA surrounded by analog and digital converters. This is so common that Opal Kelly — a producer of FPGA tools — launched the SYZYGY open standard for interconnecting devices like that. [Armeen] — a summer intern at Opal Kelly — did a very interesting open source FPGA-based signal generator using a Xilinx FPGA, and a SYZYGY-compliant digital to analog converter.

As you might expect, [Armeen] used a lot of Opal Kelly hardware and software in the project. But the Verilog code (available on GitHub) shows a lot of interesting things including some very practical example code for using Xilinx CORDIC IP,  which is a great way to do high-order math using digital logic.

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Smartphone Bench Instrument Apps: Disappointment Or Delight?

If you are interested in electronics or engineering, you’ll have noticed a host of useful-sounding apps to help you in your design and build work. There are calculators, design aids, and somewhat intriguingly, apps that claim to offer an entire instrument on your phone. A few of them are produced to support external third-party USB instrument peripherals, but most of them claim to offer the functionality using just the hardware within the phone. Why buy an expensive oscilloscope, spectrum analyzer, or signal generator, when you can simply download one for free?

Those who celebrate Christmas somewhere with a British tradition are familiar with Christmas crackers and the oft-disappointing novelties they contain. Non-Brits are no doubt lost at this point… the crackers in question are a cardboard tube wrapped in shiny paper drawn tight over each end of it. The idea is that two people pull on the ends of the paper, and when it comes apart out drops a toy or novelty. It’s something like the prize in a Cracker Jack Box.

Engineering-oriented apps follow this cycle of hope and disappointment. But there are occasional exceptions. Let’s tour some of the good and the bad together, shall we?

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