Hayling Island

Hayling Island

Thursday, June 12, 2014

GALs ..

So anyway, was messing about with the synth boards again. I have been experimenting with Mozzi, which is a sound synth library for Arduino. I am using ATMega328 on my VCLFO board, and I now have a multi-waveform LFO that has both voltage control of the waveform as well as the speed. It's pretty easy with Mozzi to drive a PWM output.

I put a filter on the original board design so the PWM output doesn't have much residual breakthrough of the sampling frequency (outside of my hearing anyway). However I wanted to play with a real DAC rather than the PWM thing, so I have been playing with some parts.

I have an AD5668 (8 channel 16-bit SPI DAC) which is in a tiny TSSOP package. It's too expensive though, to be used everywhere. I have decided to commit that board to the digital waveform generator for arbitrary waveforms in the audio range, rather than for control. I have also tried an MPC4922, a two-channel 12 bit DAC and I might use that for the MIDI to CV function.

When I took a Roland E10 apart a while ago (wasn't worth saving, except the keyboard mechanism) I found a PCM54 16-bit single channel DAC in there. I also have a drawer full of old components from a failed programme at work - where I used to work 20 years ago - including some LF398 sample and hold modules, so that is now being prototype boarded up as a daughter board for the LFO board.

Of course integrating a linear, 16-bit parallel input DAC to an ATMega with most of its pins used isn't easy, but in the search for the sample and holds, I came across a box of GAL16V8, 20V8 and 22V10. So I spent a happy morning digging out the old ALL-11P programmer, installing WACCESS, the All-11P software under WINE on Fireball, my linux machine here, installing Lattice ispLever Classic software for programming 'obsolete' devices like the GALs using Verilog, and starting to write bits of code to turn 22V10 into an SPI interface. The result is a bit of Frankenstein's Monster creation, but it should work.

I used to have a choice of programmers, but I sold two on eBay a while ago and I trashed the two I made. There was some sentimental value to having an old prototype board with a variety of ZIF sockets on it, and a step-up SMPS, along with some MC1408 DACs to set the voltage levels, but quite frankly, Hi-Lo and their All-11P is pretty, works .. 

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