MonoVoice

A SID based MIDI Synthesizer !

Courtesy/Thanks to: Buchi

Description: From the site:

After my efforts of connecting a Commodore SID chip to the PC parallel port, i had several people asking how to interface that thing to a sequencer or keyboard. So i had to write some kind of MIDI loopback driver for it; but i did not like that idea and built a standalone box instead: the MonoVoice.

My first idea was to make it 3-voice polyphonic beacuse it has 3 independent oscillators, but then i changed to the idea of a monophonic synth with a three-oscillator voice.

The SID chip is connected to an AVR AT90S8515 Microcontroller running at 8 MHz. The clock signal for the SID comes from a separate 1 MHz crystal oscillator. 16 output lines of the AVR are enough to create a complete 6502 state machine: 8 data lines come from one port, and another port carries the control signals: Reset, Read/Write, CS and 5 address lines. (Further explanation is done by studying the WRITE_SID and RESET_SID functions in the source code.

Warning to all people building stuff with the SID chip: the SID´s output is very delicate. I managed to zap 3 SID chips during development by simply inserting the cable from the MonoVoice into my amp´s jack - the extremely short short circuit duting insertion can do that. So use an opamp buffer to save your SID !