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 Forum index » DIY Hardware and Software » Microcontrollers and Programmable Logic
Hybrid analog/digital module questions
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macumbista



Joined: Sep 12, 2007
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PostPosted: Sat May 12, 2012 6:03 am    Post subject: Hybrid analog/digital module questions Reply with quote  Mark this post and the followings unread

I've been looking at the Eardrill modules for the Buchla 200e system, particularly the Pendulum/Ratchet, thinking how relatively easy it would be to make something like the with an ATmega microcontroller.

So I've decided to investigate making an analog-voltage-controlled digital-clock-signal generator. But I had some questions about interfacing that with the outside world.

Firstly, ATmegas can handle an analog reading of 0-5V. So normal +/-5V analog waveforms (total 10V peak-to-peak) would have to be divided and offset. Does anyone know a way to keep the full resolution? Or would this require an external ADC?

Second, in a situation like a modular where all kinds of things get plugged in all kinds of places, usually the all the ICs have some input and output protection to prevent excessive loading, and to protect the digital chips.

For example, a CMOS IC will usually have the clock input buffered with an op-amp, and the pulse out buffered with either a transistor or an op-amp. Often there are some diodes as well to prevent negative analog waveform voltage from getting to them.

How much protection would be required to safely stick an ATmega in a +/-15V modular environment? All of the above?

And lastly, would a voltage converter on the board be enough, or should I really make a system-wide dedicated power and ground line for the digital IC?

Thanks for your thoughts!

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PickNick



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PostPosted: Mon May 14, 2012 1:57 am    Post subject: Reply with quote  Mark this post and the followings unread

hi Macumbista!

Alain already made a PIC based masterclock module:

http://www.acxsynth.com/mclock/mclockfr.htm

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macumbista



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PostPosted: Mon May 14, 2012 2:18 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the reply!

The clock I want to make will do very different things than the one you linked to. Mainly, it would produce odd and even divisions of an input pulse, as well as randomly passing the input pulse to the output pulse based on different sets of voltage controlled probabilities. No MIDI at all. Check the Eardrill page I posted for a better idea. But what it does isn't so important right now as how to connect it to the modular...

In this schematic you sent, I see that the input buffers are set up to use a +/-5V CV, and I think I see where that gets divided and offset to become 0-5V, it must be in that first op-amp pair somewhere. And maybe the second pair of op-amps provides protection from negative voltage entering the PIC? I'll have to read up on that particular op-am config. Also, no idea what pin 3 of the PIC does, but it seems important in this setup. Since I'll be using an ATmega, that would have to be factored out somehow.

And output buffers? None to be seen. Don't know if that is a good or bad thing yet. Probably bad. Since my (and my students') patching style is rather chaotic, I'd like to make sure no negative voltage gets anywhere near the microcontroller by accident via one the the outputs.

No special power line specified either, just an on-board voltage converter. Do people worry about digital clock noise in the rest of the system?

But at least here is one example, but I'm still interested in hearing other folks' replies to the questions I started with.

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mrmrshoes



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PostPosted: Mon May 14, 2012 5:38 am    Post subject: Reply with quote  Mark this post and the followings unread

I don't know if this is any help, but i've seen this schematic on the arduino page. Scaling input voltage's to 5V for digial pins

http://www.arduino.cc/playground/uploads/Learning/Level_shifting_4_arduino.pdf

Are you planning on using the arduino for this project?


looking forward to seeing how it turns out.
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