This Instructable will show you how to build a Blinquencer- a semi-random optical melody generator that uses three blinking LEDs shining on a pair of light dependent resistors to control the pitch of two simple audio circuits to create melodic and rhythmic patterns. If that sounds technical don't worry, it's a really simple project that gives impressive results and it's a great introduction to noise circuits and generative music. It also makes a cool nightlight. Check out the video and see what it does and how it sounds and read on to see how to build your own.
Aside from a couple of ICs, a few LEDs and a fresh protoboard (less than $1 worth of stuff), I used all recycled and repurposed parts and materials for this project. It is designed to run from batteries for portability or a recycled wall wart for use around the house. While you could build a similar device from all new parts, I wish to demonstrate that money doesn't have to be a factor in electronics exploration and creation- save your money for better tools!
When I got into noise circuits, one of the first interfaces I learned was using a light dependent resistor to control the pitch of an oscillator. Basically, an LDR acts like a light controlled potentiometer- the brighter the light falling on the sensor, the lower the resistance. The darker it is, the higher the resistance. Total darkness blocks practically all current, acting like a switch. By using a LDR for the resistor in a typical R/C inverter oscillator, you can control the rate or pitch of that circuit with light.
I began to experiment with various light sources such as TVs and monitors, Christmas lights, strobes, flashlights and anything else that blinked, glowed or lit up. I eventually saw the Bleep Labs' Thingamagoop with its blinking LED on a flexible wire stalk that used a photosensor to affect the sound produced. This inspired a lot of my own projects like the one featured here. By having the LED on the end of a semi-rigid wire, you could use distance and position of the light source to control the amount of light falling on the sensor. If you have multiple stalks with LEDs you can switch them on and off and get different notes from a sound circuit with an LDR.
This project uses a CD40106 chip. This is a basic CMOS logic gate which is one of the building blocks of modern computers and digital devices. This is a digital circuit. Digital circuits read and create signals which turn off and on at controlled times. This creates a series of 'on' and 'off' signals, which can represent a binary code. While CMOS logic gates are primarily used for computations and data routing, they can be used to create sounds*. This circuit uses oscillators, circuits which turn off and on at an even, controllable pace. At slower rates these circuits are called clocks and can be used to measure divisions of time. If you listened to the signal created by a low speed oscillator it would sound like a steady stream of even clicks. If we sped this oscillator up the clicks would get closer and closer together until it created a steady buzz, like a snare drum roll. If you continued to speed the signal up it would begin to sound like notes- the faster the oscillator, the higher the note. By carefully controlling the speed of the oscillator we can get specific notes and even melodies.
The CD40106 consists of six inverters. An inverter has an input and an output. If you put an 'on' signal (called a '1' in binary language) into the inverters input, it will give the opposite output- in this case an 'off' (or '0'). In very simple terms, our circuit detects a 0 (power off) on its input pin and gives a 1 (power on) on its output pin. This 1 (power on) goes through a simple resistor/capacitor combo that builds up a charge and then releases it back to the inverter's input. This is read as a 1, or 'on' signal, causing the inverter to change its output to 0 or 'off'. This causes the R/C circuit to drain and stop discharging to the input pin, causing it to read as 0 again. This happens over and over again. The values of the resistor and capacitor used will control the speed at which the oscillator cycles back and forth between on and off, 1 and 0. This even on/off signal is called a square wave and is the basis for many synthesizer and sound circuits as well as many non-audio circuits.
Since the CD40106 has six separate inverters we can use it to make six independent oscillators that cycle at different rates. We will use three inverters with potentiometers to control the rate of three blinking LEDs. These LEDs shine onto two light sensitive resistors which control the pitch of two audio oscillators built from two more of the inverters. The final inverter is used to build an LFO or low frequency oscillator that turns the output of the two audio oscillators on and off quickly for tremolo and rhythmic effects at a rate controlled by a potentiometer. By carefully adjusting the pitch of the audio oscillators, the speed of the three blinking LEDs and the rate of the LFO, interesting musical and tonal patterns evolve and change over time.
Sound fun? Here we go...
* A note on CMOS sounds-
For a look at what CMOS logic chips can do check out this short clip of my Lunetta synthesizer. Lunetta's, named for creator Stanley Lunetta, use CMOS logic chips and an open patchable system of connections to create tones, patterns, control voltages and raw, amazing sounds. Lunettas are the opposite of traditional synthesizers- while a Moog is used to create sounds, a Lunetta is used to discover them. There's an amazing community of enthusiasts over at electro-music.com who are more than happy to introduce you to the wonderful world of digital noise and generative music.