[Mark] had seen a few examples of algorithmic music generation that takes some simple code and produces complex-sounding results. Apparently it’s possible to pipe the output of code like this directly to audio devices on a Linux box, but [Mark] decided to go a different direction. His project lets you play simple algorithms as audio using AVR microcontrollers.

Now the code work for this is very simple, but he hardware implementation is where things get interesting. Ostensibly, [Mark] didn’t have the components available to build a filter to use PWM as an audio signal. Being that he’s a ham operator, he grabbed some radio equipment he had on hand and whipped up an alternative. He’s feeding the PWM from an Arduino into the voltage controlled oscillator on a board meant for high-altitude balloon telemetry. The signal broadcast by this board is then picked up by his radio receiver, and played on some speakers.

Rube-Goldberg contraptions aside, the effect is pretty interesting, as you can hear in the latter half of the video clip which we’ve embedded after the jump.

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[Leigh] is a HAM operator (you may know him as wa5znu). He is familiar with a signal visualization tool called a waterfall which plots signal strength and frequency over time. He wanted to build his own waterfall and ended up with this Arduino-based version which he calls Cascata. Cascata means waterfall in Italian which meshes nicely with Arduino’s country of origin

The display he chose is a Nokia LCD shield from SparkFun. It’s easy to plug in and there were already libraries available to drive the display. The audio input just connects to a headphone plug (you can just make it out at the bottom right in the image above) using some electrical tape. A free-formed resistor divider ensures that the signal is within a measurable range. [Leigh] found that signal noise was a bit of a problem but was able to improve his results by adding a capacitor to the Arduino headers between the VREF and GND pins.

See it in action after the break.

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Instructables user [Rudolf] wrote in to share a handy little tool he created with ham radio operators in mind. Now and again, he found himself connecting to an unknown power supply, and rather than blow out all his expensive radio gear, he decided to put together a simple polarity and voltage tester that can be easily carried out in the field.

The tester features a pair of powerpole connectors, which are used quite often for connecting HAM gear. A PIC12F675 runs the show, acting as an adjustable comparator for detecting voltage levels. By default, his probe glows amber when the supply voltage is below 11.5V, turning green when the supply is between 11.5V and 15V. When the detected voltage is too high, the built-in LED glows a bright red. When the polarity is reversed, the LED flashes red regardless of the supply voltage.

All of these trigger levels can be set in the PIC’s code, which [Rudolf] is kind enough to include on his page, along with schematics for making your own.

[Bill Meara] was watching the International Space Station and the Shuttle Discovery pass overhead a few weeks ago, which rekindled an interest he gave up long ago – sending and receiving radio packets from space.

Years ago, he used to send APRS packets into space with a small rig powered by a 286 computer and HandiTalkie. These packets would drift off into space most of the time, but occasionally they would bounce back to Earth whenever the space station or PC Sat would fly by. The packets were often captured by other ham operators across the globe, who happened to be tuned to 145.825 MHz.

His interest renewed, he dug out his old HandieTalkie and Kantronics Terminal Node, aiming them towards the sky via an antenna situated in his back yard. When he returned 10 hours later, he found that he had collected all sorts of “space packets” from across the globe.

While not exactly a hack, it is definitely a neat exercise in ham radio operation. We can imagine slinging data packets off the space station would be an exciting experience for any budding operator (and OMs as well!)

[Colin] wanted a way to reliably control an Arduino via ham radio. One of the easiest methods of automated radio control makes use of Dual-Tone Multi-Frequency signalling. To those who aren’t into amatuer radio you probably recognized DTMF as the touch-tone system for telephone communications. [Colin] built a shield that has an audio input and can decode DTMF signals.

The hardware is based around an MT8870 DTMF decoder chip. This is a popular choice for DTMF hardware because it does all of the decoding work for you. Whenever a valid tone is detected it outputs the associated value in binary on four output pins. There is a fifth pin that strobes after each new tone. [Colin's] design offers a lot of feedback for what’s going on with the input signal. The DTMF value is displayed on a 7-segment display (controlled completely in hardware), the value is output on for Binary Coded Decimal pins, and mapped to a set of ten pins which pull to ground to match the digit received.

Low bandwidth speech compression is a desirable concept for amateur radio enthusiasts. Unfortunately there isn’t a great open-source option out there, but that’s changing with the low-bitrate speech compression package called Codec2. It manages to transmit and decode at 2550 bits per second with results comparable to proprietary solutions like MELP and very near the initial goal of 2400 bit/s. [David Rowe], who spearheads the project, has been simulating communications using a Linux box and has posted audio snippets at the first link above for comparison. They’re looking for feedback and testing so if you interested give them a helping hand.

[Thanks Robomo]

[dajjhman] wrote in to show us how he added a microphone jack to the handset of his Yaesu radio while retaining the DTMF functions. He states that there were some adapters available on the market, but they are non standard and didn’t really fit his needs. The modification itself is pretty simple, especially with his great documentation and clear pictures. For anyone else who might need this setup, this should be a great resource.

[W1VLF] is on a quest to communicate over long distances with a 9 kilohertz transmitter. He built this giant coil with that in mind. A round concrete form was used as a base and wound with magnet wire by hand. We’d recommend building an automated winding device, but this method seems to have worked. Operating at 50 Watts on the air-core coil at 8.97 KHz he was able to pick up the signal at a distance of 5 kilometers. It’s not breaking any overall distance or portability records, but on a project like this the quest is where the fun is at.

[Thanks Drone]