Well, I have deemed the FPGA Synthesizer “done”, at least in its current revision. I have still not lit up the MIDI port, but I don’t think I want to write a bunch of MIDI code in 6502 asm, so for now I have put the project on ice. It has exceeded all my expectations at this point.

So far, it plays the following stuff (all in hardware):

.NSF (complete with support for NES, VRC6, VRC7, FME7, N106, MMC5, FDS expansion audio)
.SID (complete, with quad-SID support, filters, RSID, PSID, and Compute! Gazette MUS format)
.GBS (complete, with normal Gameboy and Gameboy Colour support)
.SAP (complete, with dual POKEYs)
.SGC (complete, with support for SN76489, Colecovision, SMS, Gamegear modes)

It also plays a variety of FM music formats through a Verilog’d OPL3 (.CMF, .RAW, .IMF, .WLF, .D00)

Internally the following sound chips are written in Verilog by me:

6581/6582/8580 SID (quad, with full filters, full combined waveforms, proper ADSR w/ original bugs, 95% of a C64 to run RSID tunes, hardware filters)
RP2A03G NES (all expansion chips supported: VRC6, VRC7, FME7, N106, MMC5, FDS)
POKEY (As found on the Atari 8 bit line)
SN76489 (used for GG/SMS/Coleco)
AY-3-8910 (Written, but not used by a replayer yet)
OPL3 (FM support, can play OPL2 music also)

There’s around 70 or 80 separate sound channels that eventually get mixed down inside to the final DAC outputs. Most outputs have full user control of volume and channel selection, and if it gets filtered by the hardware filters or not.

The packaging was finally finished, along with the capacitive touch panel for the user interface. Battery charging and control are likewise finished, and I ended up implementing a first order derivative for the end of charge detection. Voltage depression isn’t very detectable on NiMh cells, so I couldn’t use that easily. The PIC’s ADC was too noisy to pick up the changes, so I went with delta temperature over delta time. When temp rise hits 3 degrees/minute, the charging is terminated. It works very well and doesn’t detect false ends of charge. There’s also a maximum temperature cutoff and a maximum time cutoff in case of some other kind of failure.




This is the UI PCB, it is a capacitive touch based affair.




Front of the finished synthesizer.




Side view.




Back view, showing power button and charge LED.




The guts.


So that’s the finished result. It didn’t come out too bad after all, but I did have to hack up the UI PCB some to make it work- Specifically I had to mount it on the top of the box and run wires to a cut up PCB inside that has the touch chip on it. The plastic was just way too thick on the enclosure for it to work through the plastic, unfortunately. But, the end result is pretty nice and the capacitive touch stuff works extremely well, so in the end it all worked out.

I will be working on a new synthesizer sometime in the future, which will be programmed in C, making development alot easier. Midi’s being reserved for that time.