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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
"OPTORGAN" - Optically triggered two octave CMOS organ
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Joined: Feb 02, 2010
Posts: 266
Location: California

PostPosted: Tue Jan 13, 2015 6:31 pm    Post subject: "OPTORGAN" - Optically triggered two octave CMOS organ Reply with quote  Mark this post and the followings unread



Hi Guys, been a while since I checked in here.

I wanted to share this little guy with you. This is an idea that's been in the works for a while but which I just finally finished to use in conjunction with my audio/video performances.

The core here is 6 oscillators built on a single 40106 chip, with each oscillator running to a 4040 divider. The outputs are taken from the /2 and /4 outputs of the 4040s providing a total of two octaves from each oscillator (12 outputs: the original oscillator signal does not appear on the output of the device).

Each output from the six 4040s is gated on and off by a 4016 analog switch controlled by an optical sensor (light dependent resistor). The sensors have the +voltage (12v) on one pin, and the other pin of each sensor goes to the switching input of a 4016 analog switch. When enough light is present on the sensors, their resistance value drops low enough to allow enough voltage to pass and flip the switches on the 4016 to "on."

I experimented with different pull-down values for the control inputs of the 4016, and 10K provided the appropriate sensitivity setting for use with a video monitor in close proximity. 1K resistors did not allow enough sensitivity for that configuration. Although the control inputs on the 4016 are intended to be strictly on/off, I do find that there is a slight "knee" to the switching, which actually makes for nice smooth sounding envelopes as light moves across the sensors. It really acts quite nicely as a VCA, and I am tempted to try some other experiments with it (on a related note, I also got interesting pitch sweep results by feeding sweeping variable voltages to the gate inputs on gate-able oscillators set up on 4093 chips). With fast flickering material, the response is still quite fast here.

The corresponding signal gates of the 4016 send the signal to a passive resistor mixer to sum the 12 signals, and finally through a "big muff" style tone control (a sort of passive bandpass filter).

I had to use quite a hefty laptop power supply (4.5A), and used an LM317 voltage regulator to maintain a steady flow of voltage at 12V. I tried with a much lower current power supply (200mA), and it would only gate on three of the switch inputs from the sensors simultaneously. I believe that the LDRs suck quite a lot of current when you feed the +V straight into them.

I am quite happy with the results and find that now that the kinks are worked out with power supply and pull-down resistors, it works pretty much exactly as expected. One other note is that LCD screens seem to work the best as it seems that CRT has a flicker which becomes audible via the sensors gating the signal on and off at 60Hz.

This video shows first the device being manually "played," and then the results of the Optical Organ being played by various video signals (all from live video feedback sources).

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RingMad



Joined: Jan 15, 2011
Posts: 427
Location: Montreal, Canada
Audio files: 4

PostPosted: Wed Jan 14, 2015 5:55 am    Post subject: Reply with quote  Mark this post and the followings unread

Wow, that's pretty cool! I like the timbre too, especially in the part where it's played by the feedback images... musically it reminds me of Terry Riley a bit.

That's crazy about the power consumption.

And maybe a simple notch filter at 60 Hz would help with CRT usage?

The video is too short though Smile

.: James :.
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Joined: Feb 02, 2010
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Location: California

PostPosted: Thu Jan 15, 2015 3:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

I actually recorded this really nice long minimalist phasing loop type of thing shortly after finishing it, but the tape got stuck in the VCR and I haven't been able to get it out. Sad

Terry Riley definitely an influence both in timbre and structure.

I will probably have some longer full pieces online sometime in the next year. Smile

I don't know if it is sucking up the full 4.5A but it does definitely require a bit.

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