Acrobotic Industries is currently selling an ATmega328-powered sound synthesizer kit for a cool $35.
The kit includes all components needed for assembling a monophonic synthesizer. Aside from Atmel’s ATmega328 microcontroller (MCU), key specs and features include:
- Dual oscillators
- 6 wave forms (Sin, Triangle, Left Saw, Right Saw, Square, and Flat)
- Noise setting on the main oscillator
- Adjustable (weighed) mixing of the two oscillators
- Adjustable cents, semitone, and octave for the second oscillator
- Low Frequency Oscillation (LFO) from 0 to 100Hz
- Routing the LFO to semitone, cents and octave control of the second oscillator
- 20 note arpeggio feature with adjustable speed from 0 to 50Hz
- 5 banks for saving presets
- 3.5mm aux output with volume control
- LCD screen with backlight control (Nokia 5110)
- MIDI input for connecting a keyboard
- UART input for serial communication (e.g., using an FTDI breakout board)
Originally designed by Human Hard Drive (Sam Stratter), the synthesizer was inspired by the DDS signal generator detailed by Martin Nawrath of the Cologne Academy of Media Arts.
Essentially, a stable clock drives a programmable-read-only-memory (PROM) which stores one or more integral number of cycles of a sinewave (or other arbitrary waveform, for that matter).
As the address counter steps through each memory location, the corresponding digital amplitude of the signal at each location drives a DAC which in turn generates the analog output signal.
The spectral purity of the final analog output signal is determined primarily by the DAC, while the phase noise is basically that of the reference clock.
You can pick up the ATmega328-powered sound synthesizer kit for $35 here, while additional information about the Direct Digital Synthesis method is available here.
Atmel | Bits & Pieces 