oscillator

92 Articles

A No-Calibration Metal Detector

July 17, 2022 by 12 Comments

A traditional early project for someone discovering a love for electronics has been for many years a metal detector. This would mean a few transistors back in the day, but today it’s more likely to involve a microcontroller. [Mircemk] has an example that bends both worlds, with a single transistor oscillator and an Arduino.

This type of metal detector has a large search coil which forms part of the tuned circuit in an oscillator. As a piece of metal enters its range the frequency of oscillation changes. In the old days, this would have been detected as an audible beat frequency with another oscillator. This design would require a calibration step at the start of detecting, to tune the two oscillators to the same frequency.

This detector keeps the first oscillator but eschews the second one in favor of an Arduino. The microcontroller acts as a frequency counter, monitoring the frequency and issuing an alarm when it detects a change likely to be caused by a piece of metal. It may not have some of the finess a human ear could apply to a beat frequency in the all-analogue days, but it’s simple enough to build and it avoids the need for calibration. Seeing it in the video below the break we’re sure that just like those transistor models old, there will be plenty of fun to be had with it.

An Arduino may be one of the current go-to parts, but will it ever displace the 555? Perhaps not in the world of metal detectors!

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Relax And Enjoy This Simple Drone Synthesizer

May 29, 2022 by 2 Comments

You’d think that a synthesizer that makes as much noise and sports as many knobs as this one would have more than a dozen transistors on board. Surely the circuit behind the panel is complex, and there must be at least a couple of 555 timers back there, right?

But no, the “Box of Beezz” that [lonesoulsurfer] came up with is remarkably simple. It takes inspiration from a [Look Mum No Computer] circuit called the “Circle Drone of Doom,” which used six switchable relaxation oscillators to make some pretty cool sounds. The Box of Beezz steps that up a bit, with four oscillators in three switchable banks in the final version. Each oscillator has but one transistor with a floating base connection and a simple RC network on the collector. The sawtooth outputs of these relaxation oscillators can be adjusted and summed together, resulting in some surprisingly complex sounds. Check out the video below for a bit of the synth’s repertoire — we’d swear that there are points where we can hear elements of the THX Deep Note in there.

We poked around a bit to understand these oscillators, and it looks like these qualify as avalanche relaxation oscillators. [lonesolesurfer]’s notes indicate that SS9018 transistors should be used, but in the photos they appear to all be 2N4401s. We’re not sure how long the transistors will last operating in the avalanche mode, but if they quit, maybe some neon tubes would work instead.

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DIY Metal Detector Gives You The Mettle To Find Some Medals

May 2, 2022 by 23 Comments

Hurricane season is rapidly approaching those of us who live in the northern hemisphere. While that does come with a good deal of stress for any homeowners who live in the potential paths of storms it also comes with some opportunities for treasure hunting. Storms tend to wash up all kinds of things from the sea, and if you are equipped with this DIY metal detector you could be unearthing all kinds of interesting tchotchkes from the depths this year.

The metal detector comes to us from [mircemk] who is known for building simple yet effective metal detectors. Unlike his previous builds, this one uses only a single integrated circuit, the TL804 operational amplifier. It also works on the principle of beat-balance which is an amalgamation of two unique methods of detecting metal.  When the wire coils detect a piece of metal in the ground, the information is fed to an earpiece through an audio jack which rounds out this straightforward build.

[mircemk] reports that this metal detector can detect small objects like coins up to 15 cm deep, and larger metal objects up to 50 cm. Of course, to build this you will also need the support components, wire, and time to tune the circuit. All things considered, though it’s a great entryway into the hobby.

Want to learn more about metal detecting? Check out this similar-looking build which works on the induction balance principle.

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Vacuum tube Atari Punk Console

The Atari Punk Console, Now With More Vacuum Tubes

January 11, 2022 by 7 Comments

Most of us have beheld the sonic glory of an Atari Punk Console, that lo-fi synth whose classic incarnation is a pair of 555 timers set up to warble and bleep in interesting ways. Very few of us, however, have likely seen an APC built from 555s that are made from vacuum tubes.

It’s little surprise to regular readers that this one comes to us by way of [David] at Usagi Electric, who hasn’t met a circuit that couldn’t be improved by realizing it in vacuum tubes. His “hollow-state” Atari Punk Console began with the 18-tube version of the 555 that he built just for fun a while back, which proved popular enough that he’s working on a kit version, the prototype of which served as the second timer for the synth. With 32 tubes aglow amid a rats-nest of jumpers, the console managed to make the requisites sounds, but lacked a certain elegance. [David] then vastly simplified the design, reducing the BOM to just four dual-triode tubes. Housed on a CNC milled PCB in a custom wood box, the synth does a respectable job and looks good doing it. The video below shows both versions in action, as well as detailing their construction.

As cool as a vacuum tube synth may be, we realize that not everyone goes for the hot glass approach. No worries — plenty of silicon Atari Punk Consoles to choose from here. There’s one built into a joystick, a circuit sculpture version complete with mini-CRT, or even eight APCs teamed up with MIDI control.

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Dub Siren, a 555-powered synthesizer

Classic Chip Line-Up Powers This Fun Dub Siren Synth

September 24, 2021 by 8 Comments

There’s a certain elite set of chips that fall into the “cold, dead hands” category, and they tend to be parts that have proven their worth over decades, not years. Chief among these is the ubiquitous 555 timer chip, which nearly 50 years after its release still finds its way into the strangest places. Add in other silicon stalwarts like the 741 op-amp and the LM386 audio amp, and you’ve got a Hall of Fame lineup for almost any project.

That’s exactly the complement of chips that powers this fun little dub siren. As [lonesoulsurfer] explains, dub sirens started out as actual sirens from police cars and the like that were used as part of musical performances. The ear-splitting versions were eventually replaced with sampled or synthesized siren effects for recording studio and DJ use, which leads us to the current project. The video below starts with a demo, and it’s hard to believe that the diversity of sounds this box produces comes from just a pair of 555s coupled by a 741 buffer. Five pots on the main PCB control the effects, while a second commercial reverb module — modified to support echo effects too — adds depth and presence. I built-in speaker and a nice-looking wood enclosure complete the build, which honestly sounds better than any 555-based synth has a right to.

Interested in more about the chips behind this build? We’ve talked about the 555 and how it came to be, taken a look inside the 741, and gotten a lesson in LM386 loyalty.

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Teardown: Franz Crystal Metronome

June 22, 2021 by 16 Comments

I wish I could tell you that there’s some complex decision tree at play when I select a piece of hardware to take apart for this series, but ultimately it boils down two just two factors: either the gadget was something I was personally interested in, or it was cheap. An ideal candidate would check both boxes, but that’s not always the case. This time around however, I can confidently say our subject doesn’t fall into either category.

Now don’t get me wrong, at first glance I found the Franz Crystal Metronome to be intriguing in its own way. With that vintage look, how could you not? But I’m about as far from a musician as one can get, so you’d hardly find a metronome on my wish list. As for the cost, a check on eBay seems to show there’s something of a following for these old school Franz models, with ones in good condition going for $50 to $80. Admittedly not breaking the bank, but still more than I’d like to pay for something that usually ends up as a pile of parts.

That being the case, why are you currently reading about it on Hackaday? Because it exploits something of a loophole in the selection process: it doesn’t work, and somebody gave it to me to try and figure out why. So without further ado let’s find out what literally makes a Franz Crystal Metronome tick, and see if we can’t get it doing so gain.

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Reliable Frequency Reference From GPS

February 28, 2021 by 35 Comments

GPS technology is a marvel of the modern world. Not only can we reliably locate positions on the planet with remarkable accuracy and relatively inexpensive hardware, but plenty of non-location-based features of the technology are available for other uses as well. GPS can be used for things like time servers, since the satellites require precise timing in order to triangulate a position, and as a result they can also be used for things like this incredibly accurate frequency reference.

This project is what’s known as a GPSDO, or GPS-disciplined oscillator. Typically they use a normal oscillator, like a crystal, and improve its accuracy by pairing it with the timing signal from a GPS satellite. This one is a standalone model built by [Szabolcs Szigeti] who based the build around an STM32 board. The goal of the project was purely educational, as GPSDOs of various types are widely available, but [Szabolcs] was able to build exactly what he wanted into this one including a custom power supply, simple standalone UI, and no distribution amplifier.

The build goes into a good bit of detail on the design and operation of the device, and all of the PCB schematics and source code are available on the projects GitHub page if you want to build your own. There are plenty of other projects out there that make use of GPS-based time for its high accuracy, too, like this one which ties a GPS time standard directly to a Raspberry Pi.