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 Forum index » DIY Hardware and Software » Developers' Corner
Midi to CV via RS232?
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Kenneth



Joined: Apr 16, 2009
Posts: 43
Location: Stockholm, Sweden

PostPosted: Wed May 13, 2009 12:03 am    Post subject: Midi to CV via RS232? Reply with quote  Mark this post and the followings unread

The RS232 (printer port) has got 8 bits strait out +10 volts...

Say you put a resistor on each, large one for LSB and then the half for next bit and so on. The same tech was used long ago to output 8-bit samples on computers with no soundcards, did not sound good but it worked.

If you use all 8 bits you can have 21 octaves (12*21=252), more than needed so the last bit you can use for gate and still have 10.5 octaves.

Or use quarter intervals so you can have a little "portamento", but gate must be the better choise.

One must also have a patch in the midi software that picks the notes/gate and put it on the RS232 but that can't be hard to implement.

Did anyone try this? Maybe someone even got a PCB?

---------

I also had thoughts about the soundcard, it is a 16 bit D/A, it must be possible to use that for CV as is with wery few extra components... Or?
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Blue Hell
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PostPosted: Wed May 13, 2009 1:50 am    Post subject: Reply with quote  Mark this post and the followings unread

Could be done on the printer port, and people have been doing that in the past. There are general purpose drivers for that port and with a little programming and by using virtual midi port software (MidiYoke) it would not be too hard to make something.

It's not the rs232 port though, rs232 is a serial thing. The port used to be called Centronics port in the past and that one is indeed an 8 bit parallel port. And it even has a couple of control lines, one of them generating a strobe when a new value is put on the outputs.

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Blue Hell
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Joined: Apr 03, 2004
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Location: The Netherlands, Enschede
Audio files: 143
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PostPosted: Wed May 13, 2009 1:51 am    Post subject: Reply with quote  Mark this post and the followings unread

Oh, re. the soundcard, usually those are AC coupled and so not suitable for putting out DC values. There are DC coupled sound cards though (but rare) and people have been removing the coupling capapcitor from soundcards as well to make 'm DC.
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Kenneth



Joined: Apr 16, 2009
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Location: Stockholm, Sweden

PostPosted: Wed May 13, 2009 2:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes, I'm confusing RS232 for Centronics Smile

I will look at that as an project.

Sondcard; S&H then?, but you will need a trig so now things are getting away from the easiness I was looking for...


BTW: not related to this at all but your location but did you ever hear about Erik Akkersdijk?, he is the fastest speedcuber in the world and he is living in Enchede, I know him well, he once came to a competition me and my brother was hosting here in Stockholm Razz
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slabman



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PostPosted: Wed May 13, 2009 3:08 am    Post subject: Parallel port to CV? Reply with quote  Mark this post and the followings unread

Here you go -

http://www.cgs.synth.net/modules/cgs11_da_converter.html
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Blue Hell
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PostPosted: Wed May 13, 2009 6:10 am    Post subject: Reply with quote  Mark this post and the followings unread

Kenneth wrote:
Erik Akkersdijk?, he is the fastest speedcuber in the world


No but I do know Mark Waterman who once was fastest, or very fast at least, and lived in Enschede at the time Shocked Laughing

A s&H wouldn't really help I think as it would be near impossible to determine the moment a sample should be taken due to inevitable pahse shifts in the signal. Using a soundcard another possible approach would be to send out a tone with a certain amplitude and then measure that amplitude to get a CV value ... you'd want a precission rectifier (a relatively simple opamp circuit) for this and a bit of filtering (just an RC would likely do).

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Kenneth



Joined: Apr 16, 2009
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Location: Stockholm, Sweden

PostPosted: Wed May 13, 2009 6:48 am    Post subject: Reply with quote  Mark this post and the followings unread

Thank's slabman... but that is far away from that easy but maybe not perfect solution I was looking for =)


Blue Hell; I see, the timing must be wery critical... now I will forget about the idéa of using a soundcar... Or? Counting in my pile of old cards right now and find I got 9 old soundcards that I do not use, maybe one of them is of the DC type?? Smile Smile Smile

---------

Mark, yes, but it was 20 years ago he retired from speedcubing, but I know his friend Guus, also from Enchede, placed second in the first ever WC in 1982, but have not met him in RL (I think he lives on the same street as Erik) I'm actually using their methods, Waterman for the 2x2x2 cube and GRS for the 3x3x3 Razz
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Blue Hell
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PostPosted: Wed May 13, 2009 8:27 am    Post subject: Reply with quote  Mark this post and the followings unread

Kenneth wrote:
but it was 20 years ago


It was a good while ago for sure Laughing

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Blue Hell
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PostPosted: Wed May 13, 2009 8:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Kenneth wrote:
Counting in my pile of old cards right now and find I got 9 old soundcards that I do not use, maybe one of them is of the DC type?? :) :) :)


Probably not, but you could take some risk then to try and modify one or two I guess.

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