A ‘breadboard’ (shown below) is a blank board with holes drilled in a grid-like pattern. These holes are conductively connected in a certain way. The rows labeled with numbers (from 1 to 64 – seen vertically in the picture) are conductive, with a non-conductive groove in the middle of the board.
The columns in between blue and red lines (seen horizontally in the picture) on the long, outer edges of the board are also conductive, with a non-conductive break where the coloured lines break. Lines and collumns that are conductive can be thought of as being ‘electrically equal’ ie. a connection made at one point along a line or row is directly connected to another along the same line or row. In the diagram below, the lines between the points indicate which areas are ‘electrically equal’.
Circuits are made up by placing components into the breadboard and connecting areas via jumper leads. The middle gap is perfectly spaced to allow integrated circuits (shortened to ICs or chips) to fit snugly onto the board. Often, a power source (such as a battery) will have its positive terminal connected to a red column and its negative terminal connected to the blue column next to it. Then, jumper leads can be used to connect one red column to the other red column and one black column to the other black column, allowing for convenient access to both positive voltage and ground.
Integrated circuits have numerous ‘legs’ protruding from the body that each serves a different purpose. Most chips have a semi-circle at one end. This determines where the pins are. There is a standardisation in numbering these ‘legs’ or ‘pins’, as follows:
The pin directly to the left of the semi-circle is the first pin. The pins on the left side then count up, until they reach the bottom left corner of the chip. The counting then continues on the bottom right hand corner up to the highest-number pin on the top right hand corner.
1. Set up the power connection (also called power bussing). Connect the red wire of the 9V battery clip to a red column. Connect the black wire of the 9V battery clip to a blue column. Connect one red column to the other red column. Connect one blue column to the other blue column.
2. Insert a 4093 chip into the breadboard across the gap in between the numbered rows. Connect pin 14 to voltage (red column bus) and pin 7 to ground (blue column bus). Connect pin 1 to voltage.
3. Connect pin 2 of the 4093 to one leg of a capacitor. Connect the other leg of the capacitor to ground.
4. Connect pin 2 of the 4093 to the inside leg of a 1MΩ pot. Connect an outside leg of the 1MΩ pot to pin 3 of the 4093.
5. Insert a 4066 chip into the breadboard across the gap in between the numbered rows. Connect pin 14 to voltage (red column bus) and pin 7 to ground (blue column bus).
6. Connect pin 3 of the 4093 to pin 13 of the 4066.
7. Bend a small jumper straight. Connect it to one end of an alligator lead. Insert the breadboard jumper so it is connected to pin 2 of the 4066 chip. Connect the other end to the signal connection (tip) of an amps input.
8. Bend a small jumper straight. Connect it to one end of an alligator lead. Insert the breadboard jumper so it is connected to ground. Connect the other end to the shield connection (sleeve) of an amps input.
9. Bend a small jumper straight. Connect it to one end of an alligator lead. Insert the breadboard jumper so it is connected to pin 1 of the 4066 chip. Connect the other end to the signal connection (tip) of an instrument / sound source output.
10. Bend a small jumper straight. Connect it to one end of an alligator lead. Insert the breadboard jumper so it is connected to ground. Connect the other end to the shield connection (sleeve) of an instrument / sound source output.
11. Turn the amp on, but the level down to zero. Connect a rechargeable 9V battery to the battery clip. Turn up the amp very slowly. If you do not hear any sound, check your connections and try replacing the capacitor or resistor with components of different values.
How does this circuit work?
This circuit is made up of two main functions - a square wave generator and a switching mechanism. By using the square wave generator to control whether an electronic pathway is open or closed (ie. whether electricity is conducted between two points), a signal from a sound source is switched on and off at a constant, periodic rate.
At any one point in time, the waveform signal from the sound source is either completely on or completely off. There is no gradient between the two states.
The 4093 is responsible for generating the square waveform. This IC is what is termed a 'quad nand gate'. It is made up of four logical units called nand gates. Like other logic gates, nand gates have two inputs, whose binary state control the binary state of a single output gate in a predetermined fashion. The term 'binary state' in this context refers to the idea of a 1 or a 0. These states are represented by a positive voltage of the same value as the power supply for a logical 1 and ground for a logical 0.
The term 'nand' is short for not and. The output only goes low (ground or logical 0) when both inputs are high (power supply voltage or logical 1). The relationship between the inputs and the output can be represented by a 'truth table'.
This table can be verbally summarised. When inputs A and B are connected to ground, the output of the nand gate is 1. When input A is connected to voltage and input B is connected to ground, the output is 1. When input A is connected to ground and input B is connected to voltage, the output is 1. It is only when both inputs A and B are connected to voltage that the output of the nand gate is 0.
Consider the logic of the following scenario. Input A of the nand gate is connected to positive voltage. Input B is connected to the output of the same nand gate. In the initial state, the input is 0, because no voltage is applied. But as soon as the nand gate 'realises' that input A is high and input B is low, the output goes high - which in turn causes the input to go high. Thus, both inputs are now at a logical 1 state. But as soon as the nand gate 'reliases' that input A is high and input B is high, the output goes low - which in turn causes the input to go low. The whole situation loops and feeds-back on itself, causing the output to constantly change between high and low. This creates an oscillating circuit that is either at ground or at positive voltage at any given point in time, which results in a square waveform.
It is value of the resistor and the capacitor that controls the speed of the oscillation. It should be noted that it is possible to build up to four oscillators using a single 4093 chip. The concept of building a square wave generator using a nand gate can be found in the following reference: pp 111-139. Collins, Nicolas 2006, Handmade Electronic Music: The Art of Hardware Hacking, TF-ROUTL.
The 4066 acts as a switching mechanism to turn an input signal on and off. This IC is what is termed a 'quad bilateral switch'. This means that it has four switches. Each switch is made up of three legs or contact pins. Two of the pins (the input / output and the output / input) act as the pathway which is either turned on or off. An additional pin controls the state of the switch. If this control pin is at positive voltage, electricity is allowed to flow freely between the two pins that make up the switching path. If the control pin is at ground, then the electricity is not allowed to flow between the two pins that make up the switching path. The term 'bilateral' means that either pin of the switch can be used as an input or an output.
If the control input of the switch is controlled by the square wave signal generated by the 4093, then the signal that is placed across the input output / and output / input pins is switched on and off at the same frequency as the square wave. By connecting a sound source to one of the switch pins and connecting the other pin to an audio output transduction system (such as a battery powered amp), it is possible to hear this effect as a ring modulation effect.