A Six-Voice Synth Built On The Raspberry Pi

Over the last few decades, audio synthesizers have been less and less real hardware and more and more emulations in software. Now that we have tiny powerful computers that merely sip down the watts, what’s the obvious conclusion? A six-voice polyphonic synthesizer built around the Raspberry Pi.

The exquisitely named ‘S³-6R’ synthesizer is a six-voice phase modulation synthesizer that outputs very high resolution (24-bit and 96 kHz) audio. It’s the product of R-MONO Lab, who have displayed interesting musical devices such as a recorder-based pipe organ in the past. This build is a bit more complex, offering up some amazing sounds, all generated on a Raspberry Pi 3.

While talk of oscillators and filters is great, what’s really interesting here is the keyboard itself. The S³-6R is using the Roland K-25m, a tiny MIDI keyboard meant to serve as a ‘dock’ of sorts for Roland’s recent re-releases of the classic Jupiter and Juno synths. Building a MIDI keyboard is not easy by any stretch of the imagination, and using this little keyboard dock is a cheap way to pipe MIDI notes into any project without a lot of fuss.

Below, you can check out the audio demos of the S³-6R. It’s a real synth and sounds great. We can only hope the software will be uploaded somewhere eventually.

Continue reading “A Six-Voice Synth Built On The Raspberry Pi”

Weather Clock Puts OLPC to Work


A clock to tell the weather? [Andrew] has created a device to do that and more. Inspired by [Sean’s] weather clock, [Andrew’s]clock displays the current weather conditions, temperature, moon phase, and of course the time. The whole project started years ago with a broken keyboard. [Andrew] wanted to try to use the keyboard controller PCB as a bidirectional computer interface. Data to the computer would go in via the key matrix. Output data would be read via the status LEDs. Cheap simple microcontroller boards like the Arduino sidelined the project for a few years, but he never completely left it behind.

With an unused OLPC XO-1 in hand, [Andrew] pulled out his old keyboard controller and started hacking. His first task was getting meaningful data out of the keyboard LEDs. He coded up his own keyboard led control library in python. On the hardware side an op amp took on the roll of a comparator to ensure proper logic levels were present. [Andrew] then hooked two LEDs up as clock and data lines to standard 74 series shift registers (most likely 74HC/HCT595). He found that his data was completely garbled due to bounce. A second shift register buffering the clock cleaned things up. [Andrew] was left with a stable 40 bits per second serial link to his shift registers. With all this done, the next step was the clock itself. [Andrew] bought a RUSCH Wall clock from IKEA, and converted the clockwork to a gear reduction for a DC motor he pulled from an old answering machine. He could now move the hands at will, but had no way to determine their position. IR break beam sensors from old printers came to the rescue.

After connecting the motor drive, [Andrew] still had a number of outputs available. A few LEDs were in his parts box, so into the project they went. 12 LEDs around the outside of the clock to display the current time. 3 LEDs hide behind the weather icons as status indicators. [Andrew’s] python software really ties this together. His OLPC grabs data from the internet and displays it on the clock. A web interface allows the user to perform manual updates on the clock and to set alarms. The alarms even incorporate speech output via eSpeak. We love the reuse and recycling of parts in this hack. The end result is a clock any hacker would be proud to display on their wall.

Continue reading “Weather Clock Puts OLPC to Work”