The Trans-Harmonium Is A Strange Kind Of Radio-Musical Instrument

Pianos use little hammers striking taut strings to make tones. The Mellotron used lots of individual tape mechanisms. Meanwhile, the Trans-Harmonium from [Emily Francisco] uses an altogether more curious method of generating sound — each key on this keyboard instrument turns on a functional clock radio.

Electrically, there’s not a whole lot going on. The clock radios have their speaker lines cut, which are then rejoined by pressing their relevant key on the keyboard. As per [Emily]’s instructions for displaying the piece, it’s intended that the radio corresponding to C be tuned in to a local classical station. Keys A, B, D, E, F, and G are then to be tuned to other local stations, while the sharps and flats are to be tuned to the spaces in between, providing a dodgy mix of static and almost-there music and conversation.

It’s an interesting art piece that, no matter how well you play it, will probably not net you a Grammy Award. That would be missing the point, though, as it’s more a piece about “Collecting Fragments of Time,” a broader art project of which this piece is a part.

We do love a good art piece, especially those that repurpose old hardware to great aesthetic achievement.

Continue reading “The Trans-Harmonium Is A Strange Kind Of Radio-Musical Instrument”

Modern Spark Gap Transmitter Uses A Rotary Gap

In the “don’t try this at home” category, [Joe Smith] builds a spark gap transmitter with a twist. The twist is that the drive power is from a signal generator attached to a FET. From there, though, things go classic using an automotive ignition coil and a tank circuit. He shows how adjusting the spark frequency changes the signal’s sound in a standard receiver.

We say don’t try this at home because the output of a transmitter like this will likely spew RF all over the place. Granted, there’s probably not much power, but it may well irritate your neighbors.

Switching to AM, you can really hear the tone from the spark frequency in the receiver. [Joe] posted some earlier videos where he made a 160-meter spark gap transmitter using an electric fly swatter. There are more details about how the tank circuits work in those videos. You can also see what the output looks like on a spectrum analyzer. You can hear what that transmitter sounds like, too.

Continue reading “Modern Spark Gap Transmitter Uses A Rotary Gap”

A Ham Radio Answering Machine

For those who grew up with a cell phone in their hand, it might be difficult to imagine a time where the phone wasn’t fully integrated with voicemail. It sounds like a fantastical past, yet at one point a separate machine needed to be attached to the phone to record messages if no one was home to answer. Not only that, but a third device, a cassette tape, was generally needed as a storage device to hold the messages. In many ways we live in a much simpler world now, but in the amateur radio world one group is looking to bring this esoteric technology to the airwaves and [saveitforparts] is demonstrating one as part of a beta test.

The device is called the Boondock Echo, and while at its core it’s an ESP32 there’s a lot going on behind the scenes. It has an audio interface which is capable of connecting to a radio given the correct patch cable; in this case with a simple Baofeng handheld unit. The answering machine can record any sounds that come in. However, with a network connection the recordings are analyzed with an AI which can transcribe what it hears and even listen for specific call signs, then take actions such as sending emails when it hears triggers like that. Boondock also plans for this device to be capable of responding as well, but [saveitforparts] was not able to get this working during this beta test.

While an answering machine might seem like a step backwards technologically, an answering machine like this, especially when paired with Google Voice-like capabilities from an AI, has a lot of promise for ham radio operators. Even during this test, [saveitforparts] lost a radio and a kind stranger keyed it up when it was found, which was recorded by the Boondock Echo and used to eventually recover the radio. Certainly there are plenty of other applications as well, such as using AI instead of something like an Arduino to do Morse decoding.

Continue reading “A Ham Radio Answering Machine”

DIY Walkie-Talkie With ESP32 And ESP-NOW

In a recent article in Elektor magazine, [Clemens Valens] describes the construction and software for an ESP32 walkie-talkie system that uses ESP-NOW for the wireless connection between units, along with a low-cost condenser microphone with a transistor-based preamplifier and an LM386 op-amp for the speaker circuit. In the ESP32 module the built-in DAC and ADC are used for audio in and output, which provide just about enough resolution for voice communication.

So why use ESP-NOW rather than WiFi or Bluetooth? Mostly because of range, power usage and convenience with no SSIDs and passwords to bother with.

The DIY Walkie-Talkie circuit diagram. (Credit: Clemens Valens, Elektor magazine)
The DIY Walkie-Talkie circuit diagram. (Credit: Clemens Valens, Elektor magazine)

ESP-NOW is Espressif’s own network protocol that uses the same underlying hardware as 2.4 GHz WiFi and Bluetooth, but focuses on more basic direct and mesh-style communication. It can be considered to be somewhat like low-level UDP with MAC address instead of IP address, which makes it useful for fire-and-forget traffic such as from IoT devices.

In the past, we’ve seen ESP-NOW control everything from fake security cameras to CNC machines. In fact, we’ve even seen it used in another walkie-talkie a couple years back.

Directional Antenna Stands Tall

When you think of directional ham radio antennas, you probably think of a Yagi, cubical quad, or a log-periodic antenna. These antennas usually are in a horizontal configuration up on a high tower. However, it is possible to build beams with a vertical orientation and, for some lower frequencies, it is far more practical than mounting the elements on a boom. [DXCommander] shows us his 40 meter two-element vertical antenna build in the video below.

A typical Yagi is just a dipole with some slightly longer or shorter elements to direct or reflect the signal. A normal vertical, however, is nothing more than half of a dipole that uses the ground as the other half. So it is possible to create reflectors and directors with a vertical-driven element.

Continue reading “Directional Antenna Stands Tall”

Powering A Cavity Magnetron, From A Battery

While vacuum electronic devices have largely been superseded over much of consumer electronics, there’s one place where they can still be found for now. The cavity magnetron is a power RF oscillator device in which electrons are induced to move in a circular path through a tuned cavity, inducing a high-power RF field, and it lies at the heart of a domestic microwave oven. They usually need a high-voltage mains transformer and a rectifier to work, but [Hyperspace Pirate] has managed to make a solid-state power supply to power one from a 12 volt battery. Better still, he’s put the resulting combo in a Care Bears lunchbox. Take a look at the video below the break.

The video starts with a potted history of the magnetron before looking at the circuit of a typical oven, which uses a single diode and a capacitor in a simple voltage multiplier. The capacitor value is adjusted to lower the power output, and a pretty thorough job is done of characterising the circuit.

The low-voltage supply starts with an XVS inverter to make the high voltage via another multiplier, but the interesting part comes with the magnetron’s heater. It’s designed for 50 or 60Hz household electricity, but there it’s receiving 40 kHz and has an appreciable impedance. The addition of a capacitor soon restores it to a reasonable performance.

In case you noticed that the ZVS converter might be improved upon, take a look at a flyback converter. Meanwhile, we should probably echo the safety message in the video that playing with magnetrons and their associated transformers can be a nasty way to die. Please take care out there!

Continue reading “Powering A Cavity Magnetron, From A Battery”

Pico-WSPR-tx Does It In Software

What do you need to make a radio transmitter? There are builds that work with just a couple of transistors. But how about a GPS-disciplined small signal beacon? You can actually get the job done for less than the cost of a fancy hamburger, thanks to [RPiks]’s pico-WSPR-tx and the Weak Signal Propagation Reporter Network (WSPR).

WSPR is a digital protocol where a beacon encodes its callsign, location, and transmitting power, and then sends it out to a network of receiving stations worldwide. The idea is to use the data coming from the beacons to determine whether radio propagation conditions are good or not; if you hear a quiet signal from afar, they’re good in that direction. [RPiks]’s beacon design simply includes a Raspberry Pi Pico and a GPS receiver. Everything else is software.

Of course, this means that it’s using the Pico’s GPIO pins for transmission. Maybe you want to add some filtering to take off the rough square-wave edges, and/or maybe you want to boost the power a little bit with an external amplifier. If so, check out our own $50 Ham column’s advice on the topic. But you don’t need to. Just a Pico and a GPS should get you working, if you want to test the WSPR waters.