Scope Traces (for the electronics geeks here)

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Daryl
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Scope Traces (for the electronics geeks here)

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My winter hobby is usually soldering some toys up, when I'm not making skirts. Here are scope traces demonstrating my latest toy which I've dubbed "Tremolotron". It varies the volume of an input sound (in this case from my Casio VL-Tone) at a rate and depth I set with knobs. Not satisfied with just creating tremolo, I gave it two channels (hence the different colour traces) so the sound can alternate between left and right for a cool depthy echoey type of effect. I also made it able to modulate the amplitude with either a sawtooth or a triangular envelope. On one channel the sawtooth envelope makes the sound like an instrument being continuously plucked or hammered. The first image is the device applying a triangular envelope. The second image is the sawtooth envelope.

Four chips were involved: a 555 timer, an LM324 quad op-amp, and two H11F1M FET-output opto-isolators. The 555 timing capacitor provides the envelope shape; the LM324 follows that voltage (without loading it) and drives the LED side of the H11F1M chips. Powered by 5v, the amplitude of the waveform from the 555 timing capacitor is almost perfect with the op-amps at unity gain. The usual handful of potentiometers, resistors and capacitors needs no explanation.
tremolotron2-600x320.gif
tremolotron1-600x320.gif
What's it good for, you ask? Listen to Donovan singing Hurdy Gurdy Man then ask again! Also, I wanted a general purpose unit that can also provide input signal for a vibrato effect on the VCO of my long term sequencer project, and also something to drive a strobe light and some other silly stuff like that. One box many purposes.

The scope is Soundcard Scope by C. Zeitnitz.
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Freedomforall
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Re: Scope Traces (for the electronics geeks here)

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Very neat! You should share pics of the skirts you make too.
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ethelthefrog
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Re: Scope Traces (for the electronics geeks here)

Post by ethelthefrog »

I always like scope traces. Out of interest, why do you pass the output through the opto isolators?
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phathack
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Re: Scope Traces (for the electronics geeks here)

Post by phathack »

ethelthefrog wrote:I always like scope traces. Out of interest, why do you pass the output through the opto isolators?
I haven't seen the circuit but I suspect that opto isolators are acting like as a variable resistance so you can vary the level based on a waveform making audio that increases or decreases in proportion to LED Drive current.


:ugeek:
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Re: Scope Traces (for the electronics geeks here)

Post by crfriend »

ethelthefrog wrote:Out of interest, why do you pass the output through the opto isolators?
Good down to DC, unlike capacitive or inductive coupling, probably.
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Daryl
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Re: Scope Traces (for the electronics geeks here)

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phathack wrote:
ethelthefrog wrote:I always like scope traces. Out of interest, why do you pass the output through the opto isolators?
I haven't seen the circuit but I suspect that opto isolators are acting like as a variable resistance so you can vary the level based on a waveform making audio that increases or decreases in proportion to LED Drive current.
:ugeek:
Bingo. Quick and dirty voltage controlled resistance.
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Daryl
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Re: Scope Traces (for the electronics geeks here)

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crfriend wrote:
ethelthefrog wrote:Out of interest, why do you pass the output through the opto isolators?
Good down to DC, unlike capacitive or inductive coupling, probably.
Yes, it is good down to DC, though that is not why I used them but rather just a handy fact given that the effects I am interested in are quite low frequency (left-right panning and vibrato and tremolo).
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Daryl
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Re: Scope Traces (for the electronics geeks here)

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Freedomforall wrote:Very neat! You should share pics of the skirts you make too.
I have, in Pics and Looks under Daryl's circles.

Also, click the first dot after my name in my signature line...
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