Obscura, an Arduino-compatible MIDI 8-bit Chiptune Synthesizer

Published on Nov 4, 2015 Arcano Systems

"Obscura is an Arduino-compatible 8-bit synth for creating Nintendo, Commodore 64, and Amiga-style chiptune music. Back the Kickstarter campaign to receive the synth as a reward. http://kck.st/1RTsKUi"

via the Kickstarter campaign:

"Obscura is an Arduino-compatible 8-bit synthesizer that allows you to create NES, C64, and Amiga-style chiptune music by simply connecting a MIDI device.

No programming is required. This monophonic MIDI synth comes programmed with software that includes 16 preset patches.

Patch 0: 12.5% duty-cycle pulse waveform

Patch 1: 25% duty-cycle pulse waveform

Patch 2: 50% duty-cycle pulse waveform

Patch 3: sawtooth waveform

Patch 4: 8-bit sine waveform

Patch 5: 4-bit triangle waveform

Patch 6: 8-bit triangle waveform

Patch 7: arpeggiated octaves (25% duty-cycle pulse)

Patch 8: arpeggiated octaves (50% duty-cycle pulse)

Patch 9: arpeggiated octaves (8-bit sine)

Patch A: arpeggiated octaves (8-bit triangle)

Patch b: vibrato (12.5% duty-cycle pulse)

Patch C: vibrato (25% duty-cycle pulse)

Patch d: vibrato (50% duty-cycle pulse)

Patch E: vibrato (8-bit sine)

Patch F: vibrato (4-bit triangle)

Users with programming experience will be able create their own custom software for Obscura using the Arduino IDE. (Obscura is based on the Arduino Leonardo platform.) Arduino pins 5, 8, 9, 10, 12, and 13 are broken out for hardware hacking and experimentation. Due to Arduino Leonardo’s native USB capabilities, the Obscura Synth can be programmed to appear as a USB mouse, keyboard, or HID, enabling interesting possibilities of unique MIDI-PC interface applications.

Unlike many other microcontroller-based synthesizers, which use pulse-width-modulation (PWM) to generate weak, noisy, low-quality audio signals, the Obscura uses an auxiliary digital-to-analog converter chip with true 8-bit quantization to produce a clear, high-quality audio signal. The Obscura is USB powered and does not require a special wall adapter with a barrel-jack type connector. The simple user interface consists of two patch control buttons, a reset button, and a 7-segment LED display. Audio is output via a standard 1/8'' (3.5 mm) stereo audio jack. (Although primarily designed to be a line out, the audio output can supply enough current to drive most headphones.)

[prototype pictured to the left]

The story the Obscura 8-bit Synthesizer begins with the Arcano MIDI NES Chiptune Synthesizer, a project launched through Kickstarter. During the Kickstarter campaign for the Arcano MIDI NES Chiptune Synthesizer, I received so many great suggestions from backers that I decided to rewrite the synth’s software to incorporate some of their ideas. Many backers told me they wanted to be able to program the synth with the Arduino IDE using only a USB cable, without the need for an AVR-ISP device or an FTDI cable. Unfortunately, this wasn’t possible with the Arcano synth's existing hardware design, so I created the Obscura, which is based on the same ATmega32u4 microcontroller used in the Arduino Leonardo.

The Obscura has gone through two hardware revisions and twelve software versions. The latest software version includes a USB serial monitor mode that is activated by holding down both preset patch control buttons during boot up. The USB serial monitor mode allows users to view the serial data output from their MIDI device on a PC or Mac for debugging and hacking purposes.

The software for the Obscura is not merely a port of the Arcano Chiptune Synth software, but was written from the ground up and uses wavetable synthesis to generate waveforms, whereas the Arcano MIDI NES Chiptune Synth generates waveforms on the fly using a series of logic statements."