Hi 
It's been a while since I was here last time, but I thought I'd post a project I've been working on for the last year or so: The NESIZER. It's basically a little synthesizer module using the 2A03 (or a 2A07 or Dendy clone). It has buttons and a display for programming patches / sounds and battery backed memory to store them. It can be played via MIDI, or sequences and tracks can be made using an in-built sequencer (not finished writing the software for that yet).
The hardware is basically centered around a microcontroller (Atmel ATmega328) doing all the work, with the 6502 just idling and updating APU registers. The idea was inspired by the TSUNDERE project which takes a similar approach which I simplified to a way that requires no external logic except for latch. Basically the ATmega328 keeps the opcode for STA zero page ($85) on the 2A03's databus to keep the 6502 busy. When an APU register is to be updated, the ATmega waits for the 6502's R/W line to go low, in which case the 6502 is in its last cycle of the STA instruction and the next cycle will be the fetch of the next opcode. The ATmega then outputs the necessary stream of instructions to load a value and store it in the desired APU register. Doing this glitch-free is achieved by having both the ATmega and 2A03 running off the same 20 MHz clock so that the two are always phase locked and there is a known and constant number of ATmega cycles for each 6502 cycle.
The hardware is pretty much completed, and I have made a few prototype PCBs. The software is still work in progress, but I'm getting there (I don't have much time to work on it now). So far I have implemented rudimentary MIDI support, three envelope generators, three LFOs, glide/portamento and coarse and fine tuning. It can also play back PCM samples at 16 kHz (samples can be sent via MIDI and stored in memory).
You can see a little demo video of it here.
The hardware and software is open source and can be found here.
I don't know what you guys think? There is a bit of interest in the synthesizer (especially DIY) community. I'm thinking of maybe making this into a DIY kit when it's finished, and maybe making an enclosure for it too.
It's been a while since I was here last time, but I thought I'd post a project I've been working on for the last year or so: The NESIZER. It's basically a little synthesizer module using the 2A03 (or a 2A07 or Dendy clone). It has buttons and a display for programming patches / sounds and battery backed memory to store them. It can be played via MIDI, or sequences and tracks can be made using an in-built sequencer (not finished writing the software for that yet).
The hardware is basically centered around a microcontroller (Atmel ATmega328) doing all the work, with the 6502 just idling and updating APU registers. The idea was inspired by the TSUNDERE project which takes a similar approach which I simplified to a way that requires no external logic except for latch. Basically the ATmega328 keeps the opcode for STA zero page ($85) on the 2A03's databus to keep the 6502 busy. When an APU register is to be updated, the ATmega waits for the 6502's R/W line to go low, in which case the 6502 is in its last cycle of the STA instruction and the next cycle will be the fetch of the next opcode. The ATmega then outputs the necessary stream of instructions to load a value and store it in the desired APU register. Doing this glitch-free is achieved by having both the ATmega and 2A03 running off the same 20 MHz clock so that the two are always phase locked and there is a known and constant number of ATmega cycles for each 6502 cycle.
The hardware is pretty much completed, and I have made a few prototype PCBs. The software is still work in progress, but I'm getting there (I don't have much time to work on it now). So far I have implemented rudimentary MIDI support, three envelope generators, three LFOs, glide/portamento and coarse and fine tuning. It can also play back PCM samples at 16 kHz (samples can be sent via MIDI and stored in memory).
You can see a little demo video of it here.
The hardware and software is open source and can be found here.
I don't know what you guys think? There is a bit of interest in the synthesizer (especially DIY) community. I'm thinking of maybe making this into a DIY kit when it's finished, and maybe making an enclosure for it too.
. I'll try it out soon.