Theo Verelst Diary Page

Latest: Februari 20 2001

I've decided after good example to write some diary pages with toughts and events.

Oh, in case anybody fails to understand, I'd like to remind them that these pages are copyrighted, and that everything found here may not be redistributed in any other way then over this direct link without my prior consent. That includes family, christianity, and other cheats. The simple reason is that it may well be that some people have been ill informed because they've spread illegal 'copies' of my materials even with modifications. Apart from my moral judgement, that is illegal, and will be treated as such by me. Make as many references to these pages as you like, make hardcopies, but only of the whole page, including the html-references, and without changing a iota or tittel...

And if not? I won't hesitate to use legal means to correct wrong that may be done otherwise. And I am serious. I usually am. I'm not sure I could get 'attempt to grave emotional assault' out of it, but infrigement on copyright rules is serious enough. And Jesus called upon us to respect the authorities of state, so christians would of course never do such a thing. Lying, imagine that.

Previous Diary Entries

February 20, 2001

The applicability of the parallel port for connecting to different systems has been experimentally verified again.

Portable system

My Z80 computer system weighs about lets say a kilogram, maybe two, depending on the breadboards and the type of supply, maybe half or so, with everything put on pcb in decent form. It has an effective circuit board area of about 4 eurocards, again depending a bit, probably including digital to analog and vv converters and the pc dma interface, and there is the calculator keyboard and the baby black and white keys keyboard.

A eurocard is 10x20 cm, so the whole thing shouldn't take excessive space, though more than the computer part of a gameboy, and it certainly comprises a lot of wires and solder. The system as it is was mainly to see what would work, and unfortunately, I'm stuck with a 10 MHz CPU, so it is basically there to do what it does because I have on alternative, and served its purpose for testing speed, bus structures, display and keyboard drivers, all things that don't obviously follow from connecting logic parts up. And of course it is nice to know that the whole circuit indeed works as intended, not that that is eventually a great surprise, I've made enough of them, and for (a lot) simpler circuits assisted many students building them easily enough, but the whole thing had various ideas in it I wanted to see work, and in the end I even got into the electromagnetical interference area, which is instructive.

And of course the whole thing also ran at 35 MHz or so, including busses, and long enough connections, with parts that are readily available, which is good experience. Currently, it is the only thing with a keyboard I have near, and it is the only computer system with at least DA converter and real time sample replay possibility, making it usefull.

It is intended as credibility raising prototype, which it can be, but it can hardly be moved at this moment, since it covers about .3 square meter desk space, and has quite some interbreadboard connections with simple wires, and not just neat multiconnectors on solid enough gp eurocard boards. And I currently can't replace some distrusted buffers (probably damaged by fridge experiment, see few pages back), so the option of making it a complete machine the way I would want at this moment is not valid enough.

I may put some stuff, including the dma parallel port interface on a circuit board instead of breadboard, and maybe some more, and load the whole machinery in a suitcase, that may be worth it.

Yesterday I had the chance to put the whole thing, and the dos software, with mouse control on another, newer, machine, and voila, the whole software and the printerport driven synth worked straight away, except the computation time for a short fourier synthesis sample with 16 linearly interpolated components, envelope generator and the filter were sort of real time, without further optimizations, and the download time such that DMA-ing (direct memory access) the whole sample in memory, with the sampler still reproducing the previous sample loop portion is just noticable as a little glitch in the sound.

That works a lot better, change a harmonic or the filter settings, and almost immedeately hear the sound change accordingly, and with still the same strong sounds. Visually, the wave window (the software is on my site if you can run dos, except you wont yet be able to generate wavs or so, I'll look into that) updates with maybe ten wave displays per second, which looks real smooth.

Even though I don't have a classy case to built the whole thing in, and wouldn't want to sell it much with the old display and prototype type of circuits in it, the sounds or synth algo's in a rom or eeprom, a bigger memory and some additional analogs circuits, and even the Z80 based thing would be good for a commercial product. Then again, the dsp lie waiting for a real prototype, which could pretty much blow away even hightech not top level competition with some work, so there is room to do more, and reason not to push this machine, but at least it does work enough to make the whole experiment completely worth it.