Logic Noise: Playing in Tune with an Exponential VCO

Last session, we use the cheap and cheerful 4046 Phase-locked Loop chip as a simple voltage-controlled oscillator (VCO). It was dead simple, in fact, because the chip has a VCO already built in. There’s one big drawback of the 4046’s VCO; the pitch changes linearly with the control voltage. Ideally, as we’ll discuss in the next sections, we’d like the frequency to be an exponential function of the control voltage (CV), and that’s going to mean a little bit of analog circuitry.

René Schmitz has a fantastic exponential VCO design that’s almost a perfect fit for the Logic Noise series — it’s built with a minimum of parts, it’s a little bit rough around the edges, and at its core is a 4000-series CMOS chip that’s normally used for digital logic applications. The only drawback, from our perspective, is that it uses a dual (positive and negative) power supply. We’ll hack our way around that, and ignore some of René’s otherwise worthwhile refinements in the name of doing something truly quick and dirty. We’ll get 95% of the results with 70% of the work, although it’s easy enough to add on the rest if it strikes your fancy.

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Logic Noise: 4046 Voltage-Controlled Oscillator, Part One

In this session of Logic Noise, we’ll be playing around with the voltage-controlled oscillator from a 4046 phase-locked loop chip, and using it to make “musical” pitches. It’s a lot of bang for the buck, and sets us on the path toward much more interesting circuits in the future. So watch the intro video right after the break, and we’ll dig straight in.

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Retrotechtacular: The Trautonium Was Elemental to Electronic Music

Electrical engineer and music enthusiast [Freidrich Trautwein] was dissatisfied. He believed that the equal tempered scale of the piano limited a player’s room for expression. And so in 1930, [Trautwein] and an accomplished pianist named [Oskar Sala] began work on an electro-mechanical instrument that would bring the glissando of the string section’s fretless fingerboards to the keyboard player. [Trautwein] called his creation the Trautonium.

Sound is produced in the instrument by sawtooth frequency generators. It is then passed through filters and manipulated by the resistive string-based manuals. Frequency and intonation are varied relative to the position of the player’s finger along a length of non-conductive string and to the amount of pressure applied. This resistive string is suspended above a conductive metal strip between a pair of posts. A small voltage is applied to the posts so that when the string touches the metal strip below, the player manipulates a voltage-controlled oscillator. A series of metal tongues, also non-conductive, hover above the string. These are placed at scale intervals and can be used like keys.

This early synthesizer is capable of producing many kinds of sounds, from crisp chirps to wet, slapping sounds and everything in between. In fact, all of the sound effects in Alfred Hitchcock’s thriller The Birds were produced on a modified Trautonium by the instrument’s one and only master, [Oskar Sala]. He went on to score hundreds of films by watching them with the Trautonium at his fingertips, recording and layering his compositions into an eerie wall of sound.

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2013 LayerOne badge hacking contest winner


[Dynotronix] wrote in to share the news that he won the 2013 LayerOne badge hacking contest. In addition to the good news he included a description of his badge hack.

We got a good look at the hardware included on the badge several days ago. You may remember that it’s outfitted with footprints for 48 LEDs around the perimeter which are driven by two ICs. Looking at the image above it’s hard to miss the fact that [Dyno] didn’t populate any of that. He went right for the power of the XMEGA processor to analyze and generate signals.

But what specifically can you do with the signal this thing generates? Turns out a rather simple circuit can make it into a transmitter. [Dyno] concedes that it’s a remarkably finicky setup, but just a few components on a scrap of copper clad turned this into an FM transmitter. Check out the video where you can hear the sweeping alarm-type sounds pushed to an FM radio via his voltage controlled oscillator circuit which has a range of about fifteen feet.

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