Making sound with a single logic chip is really quite easy. Let's take a look at the most basic sound producing circuit we cover in our serise. The full details of this are covered in the first installment of Logic Noise, but here we're going to boil it down even further. You need:

• 40106 Inverter Chip
• 2x 0.1uF capacitors
• 2x 100k potentiometer
• 1x 100k resistor
• 1x 10k resistor
• 9v battery
• powered speakers, like computer speakers
• Some way to connect everything together (a breadboard and jumper wires)

Here is a connection illustration:

When connecting your computer speakers you will also need a connection to ground (the blue lines in the diagram).

The heart of the circuit is shown below. The circuit makes sound using a concept called Hysteresis. This is a type of delay found in some integrated circuits. The 40106 chip we're using has a time delay between producing a low signal and a high signal; this is an oscillator. This change from low to high is at a frequency that produces a note. The protentiometer can change this frequency, making the sound higher or lower.