2025 Component Abuse Challenge: A Piezo Disk Powers A Transmitter

November 2, 2025 by Jenny List 12 Comments

A piezo disk transducer is a handy part for reproducing beeps and boops, and can also function as a rudimentary microphone. Being a piezoelectric element, it can also generate usable power. Enough to run a radio transmitter? [b.kainka] is here to find out, with what may be the simplest possible transmitter circuit.

The active element in the circuit, such as it is, comes from a crystal. This functions as an extremely stable and high Q tuned circuit. When excited by a pulse of electricity, the circuit will carry oscillations in a similar manner to a bell ringing until the pulse is exhausted. A small lever fashioned from a piece of wire supplies the voltage by flexing the piezo disk and a contact, a diode discharges the reverse voltage as the disk returns to shape, and a small capacitor provides an AC path to ground. It works, if a small pulse of very low-power RF near the crystal’s frequency can be described as working.

It may not be the most practical transmitter, but it’s certainly something we’ve not seen before. It’s part of our 2025 Component Abuse Challenge, for which you still have time to make an entry yourself if you have one.

Perovskite Solar Cell Crystals See The Invisible

September 16, 2025 by Heidi Ulrich 14 Comments

A new kind of ‘camera’ is poking at the invisible world of the human body – and it’s made from the same weird crystals that once shook up solar energy. Researchers at Northwestern University and Soochow University have built the first perovskite-based gamma-ray detector that actually works for nuclear medicine imaging, like SPECT scans. This hack is unusual because it takes a once-experimental lab material and shows it can replace multimillion-dollar detectors in real-world hospitals.

Current medical scanners rely on CZT or NaI detectors. CZT is pricey and cracks like ice on a frozen lake. NaI is cheaper, but fuzzy – like photographing a cat through steamed-up glass. Perovskites, however, are easier to grow, cheaper to process, and now proven to detect single photons with record-breaking precision. The team pixelated their crystal like a smartphone camera sensor and pulled crisp 3D images out of faint radiation traces. The payoff: sharper scans, lower radiation doses, and tech that could spread beyond rich clinics.

Perovskite was once typecast as a ‘solar cell wonder,’ but now it’s mutating into a disruptive medical eye. A hack in the truest sense: re-purposing physics for life-saving clarity.

Listen To The Sound Of The Crystals

July 11, 2025 by Jenny List 33 Comments

We’re all used to crystal resonators — they provide pretty accurate frequency references for oscillators with low enough drift for most of our purposes. As the quartz equivalent of a tuning fork, they work by vibrating at their physical resonant frequency, which means that just like a tuning fork, it should be possible to listen to them.

A crystal in the MHz might be difficult to listen to, but for a 32,768 Hz watch crystal it’s possible with a standard microphone and sound card. [SimonArchipoff] has written a piece of software that graphs the frequency of a watch crystal oscillator, to enable small adjustments to be made for timekeeping.

Assuming a microphone and sound card that aren’t too awful, it should be easy enough to listen to the oscillation, so the challenge lies in keeping accurate time. The frequency is compared to the sound card clock which is by no means perfect, but the trick lies in using the operating system clock to calibrate that. This master clock can be measured against online NTP sources, and can thus become a known quantity.

We think of quartz clocks as pretty good, but he points out how little it takes to cause a significant drift over month-scale timings. if your quartz clock’s accuracy is important to you, perhaps you should give it a look. You might need it for your time reference.

Header: Multicherry, CC BY-SA 4.0.

Automated Rig Grows Big, Beautiful Crystals Fast

December 12, 2024 by Dan Maloney 8 Comments

We haven’t seen [Les Wright] in a while, and with the release of his new video, we know why — he’s been busy growing crystals.

Now, that might seem confusing to anyone who has done the classic “Crystal Garden” trick with table salt and laundry bluing, or tried to get a bit of rock candy out of a supersaturated sugar solution. Sure, growing crystals takes time, but it’s not exactly hard work. But [Les] isn’t in the market for any old crystals. Rather, he needs super-sized, optically clear crystals of potassium dihydrogen phosphate, or KDP, which are useful as frequency doublers for lasers. [Les] has detailed his need for KDP crystals before and even grown some nice ones, but he wanted to step up his game and grow some real whoppers.

And boy, did he ever. Fair warning; the video below is long and has a lot of detail on crystal-growing theory, but it’s well worth it for anyone taking the plunge. [Les] ended up building an automated crystal lab, housing it in an old server enclosure for temperature and dust control. The crystals are grown on a custom-built armature that slowly rotates in a supersaturated solution of KDP which is carefully transitioned through a specific temperature profile under Arduino control. As a bonus, he programmed the rig to take photographs of the growing crystals at intervals; the resulting time-lapse sequences are as gorgeous as the crystals, one of which grew to 40 grams in only a week.

We’re keen to see how [Les] puts these crystals to work, and to learn exactly what a “Pockels Cell” is and why you’d want one. In the meantime, if you’re interested in how the crystals that make the whole world work are made, check out our deep dive into silicon.

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VNAs And Crystals

December 6, 2024 by Al Williams 7 Comments

Oscillators may use crystals as precise tuned circuits. If you have a vector network analyzer (VNA) — or even some basic test equipment — you can use it to learn the parameters of a crystal. [All Electronics Channel] has the details, and you can see how in the video below.

There was a time when a VNA was an exotic piece of gear, but these days they are relatively common. Crystal parameters are important because crystals have a series resonance and a parallel resonance and they are not at the same frequency. You also may need to know how much loading capacitance you have to supply to get the crystal at the right frequency.

Sometimes, you want to pull the crystal frequency, and the parameters will help you figure that out, too. It can also help if you have a crystal specified as series in a parallel-mode oscillator or vice versa.

If you don’t have a VNA, you can use a tracking signal generator, as [Grégory] shows towards the middle of the video. The quality of a tuned circuit depends on the Q factor, and crystals have a very high Q factor.

We did something similar in 2018. The other way to pull a crystal frequency is a bit extreme.

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Cat-o-Matic 3000 Serves Your Feline Masters

December 1, 2023 by Kristina Panos 8 Comments

When you have three cats and three humans, you have one problem: feeding them on a schedule without over or under feeding them. Even if there was only one human in the equation, the Cat-o-Matic 3000 would still be a useful tool.

Essentially, it’s a traffic light for cats — where green means you are go for feeding, and red means the cat was just fed. Yellow, of course, means the cat is either half-full or half-empty, depending on your outlook.

The brains of this operation is an ATmega88PA leftover from another project. There’s a no-name voltage regulator that steps up the two AA cells to 5 volts. Timing comes from a 32 kHz crystal that allows the microcontroller to stay in power-saving sleep mode for long periods of time.

Creator [0xCAFEAFFE] says the firmware was cobbled together from other projects. Essentially, it wakes up once per second to increment the uptime counter and then goes back to sleep. Short-pressing a button shows the feeding status, and long-pressing it will reset the timer.

Wanna make a cat status indicator without electronics? Give flexures a try.

Growing Simple Crystals For Non-Linear Optics Experiments

July 6, 2023 by Dan Maloney 18 Comments

Here’s an exercise for you: type “crystals” into your favorite search engine and see what you get. If you’re anything like us, you’ll get a bunch of pseudoscientific posts about the healing power of crystals, along with offers to buy the same at exorbitant prices. But woo-woo aside, certain crystals do have seemingly magical powers — like the ability to turn light from one color into another.

None of this is magic, of course. Rather, as optics aficionado [Les Wright] explains, non-linear optics is all about physics. Big physics, too, like the kind that made the National Ignition Facility the first fusion research outfit to reach the “break-even” point, at least in terms of optical energy. To do so, they need to convert megajoules of infrared laser beams all the way across the visible spectrum into the ultraviolet, relying on huge crystals of deuterated potassium dihydrogen phosphate (KDP) to do so. Depending on how they’re cut, crystals of these sorts have non-linear optical properties like second-harmonic generation, which combines two input photons into a single output photon with twice the energy of the original. This results in a halving of the wavelength of the input, which doubles the frequency.

While the process used at the NIF produces crystals of enormous proportions, [Les] has more modest needs and thus a simpler process. His KDP is an off-the-shelf chemical, nothing fancy about it, which is added to boiling water to make a saturated solution. A little of the solution is poured out into a watch glass to make seed crystals, and everything is allowed to cool slowly. A nice seed crystal is glued to a piece of monofilament fishing line and suspended in the saturated solution, and with enough time a good-sized crystal forms. Placed into the beam path of a 1,064 nm IR laser and rotated carefully relative to the beam, the crystal easily produces a brilliant green laser output.

This is fascinating stuff, and we’re looking forward to seeing where [Les] goes with this. Polishing the crystals to make them optically cleaner would be a good next step, as would perhaps growing even larger crystals.

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