The definitive MIDI controller | This is not rocket science

First PCBs for the DSP proto project

Circuit boards arrived by mail.

Circuit boards arrived by mail.

Today the first boards for the DSP synthesizer project arrived. Itead studio is really doing a great job with these!

I don’t want to spoil too much yet, but if this works – and probably it’ll take a couple revisions to do so – it’s going to be awesome! The bottom left board in the photo is the main DSP board with three Freescale DSPs and an NXP LPC176x. I wanted to start with something that I might possibly have a chance with, so most of the LPC features went unused for now. I also simplified the I2S buses from original plans to keep it simple. Two codecs just because I could.

On top left is the analog side with opamp filters straight from the codec datasheet, and an experimental, simple, and again rather wasteful 9V -> +/- 7.2V power supply to try in case the opamps turn out to require a greater voltage range than just +5V. I ran out of space on the main board, so this second board will be connected on top of it with the audio jacks placed through the large gap at the back edge, hanging from the analog board. And it should be possible to upgrade the codecs to better ones, only requiring a different analog board.

Top right is the MIDI/USB board, with the USB side essentially implementing a USB MIDI interface and talking to the LPC over a standard 31250 bps MIDI serial connection. I went with the 4N28 optocoupler as I had a few of them already and I’m familiar with the circuit. What I’m not so sure about is that I’m going to try to run the MIDI output with 3.3V and suitably adjusted resistors.

Bottom right board is not exactly a part of the synth, but still just as essential. I didn’t have a JTAG debugger for the DSP56k, so I designed one around the Freescale Soundbite schematic. Again, in theory it should work.

I suppose there’s a lot to optimize in the design, but first I want to see it doing something. Ah, so much uncertainty, so much fun to see how it will work out!

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