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Controlling 4 5v sq wave oscillators from Arduino
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Controlling 4 5v sq wave oscillators from Arduino

by shobley on Sat Mar 21, 2009 5:50 pm

I need to create a polyphonic Tesla coil controller that can run up to 4 square wave oscillators.

It will respond to MIDI data on 4 channels and send out oscillation/gate signals to drive the Tesla coil controller boards.

I was thinking of using an SPI digipot with a 555 timer chip - ideally this should be a "fire and forget" arrangement where I am not toggling pins on the arduino to create the waveforms. Eg - MIDI note 'X' corresponds to frequency "f" - so when a note on is received start oscillator at frequency "f" until note off.

Is there an easier way to do this without the digipot - controlling the 555 via PWM and an RC network or something?

Thanks,
Steve
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Re: Controlling 4 5v sq wave oscillators from Arduino

by Ran Talbott on Sat Mar 21, 2009 7:41 pm

For those of us who've never used Tesla coils and "music" in the same sentence: what frequencies do you need, and how precisely do you need them controlled? Do they need to match standard musical notes?

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Re: Controlling 4 5v sq wave oscillators from Arduino

by shobley on Sat Mar 21, 2009 8:41 pm

Yeah it is a bit goofy :)

My DRSSTC coil can be modulated up to about 290Hz

Yes I want to try and map MIDI events to gate/freq of musical notes. I suspect I can impletement gate by raising and lowering the reset pin (4) of the 555.

Essentially I'm trying to make a 555 timer based VCO using pin 5 (control). I was wondering if a simple RC filter on the PWM would be enough, or should I just go with a DAC.

What would be good values for the RC filter?
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Re: Controlling 4 5v sq wave oscillators from Arduino

by eil on Sat Mar 21, 2009 11:36 pm

http://www.youtube.com/watch?v=aDejvryAFN0

High-voltage toroids and MIDI on steroids. (These are a few of my favorite things.)
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Re: Controlling 4 5v sq wave oscillators from Arduino

by shobley on Mon Mar 23, 2009 9:28 am

Just FYI - I put in an RC network after the PWM and added an opamp as a voltage follower. I fed this signal into pin 5 of the 555 timer and it "kind of" works, but the Vout isn't solid enough to create a stable tone from the oscillator.

So... I think I might try some digipots as R2 of the astable configuration.

Steve
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Re: Controlling 4 5v sq wave oscillators from Arduino

by adafruit on Mon Mar 23, 2009 4:29 pm

the built in hardware PWM modules in an arduino should work well for this, up to 6 outputs.

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Re: Controlling 4 5v sq wave oscillators from Arduino

by shobley on Fri Apr 03, 2009 9:52 am

Limor,

You're the second person to mention this to me, but since the PWM outputs only control duty cycle, and not frequency, I'm not sure how to use them as a 'musical' oscillator.

If there is a way to do this, then it would be great, and waaaay easier than all the 555 malarky I'm going through...

Steve
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http://www.youtube.com/shobley
For all your laser harp, tesla coil, and killer robots from outer space needs.
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Please be positive and constructive with your questions and comments.