AC DC

No, not that AC~DC, I'm talking about Alternating Current and Direct Current.

• In our examples up to now, we have only considered Direct Current. which is current moving in only one direction along the wire, from positive to negative, just like a battery. However, the current can also reverse direction along a wire, and then we call it Alternating Current.

• For example, in the U.S.A., the Alternating Current that we get from our wall sockets reverses direction with a frequency of sixty (60) times every second, all day long. We refer to that as 60 Hertz Alternating Current

• We refer to current that reverses polarity with a regular periodicity as Alternating Current, if it is not regular, we refer to it as Pulsating, or just variable current.

Types of Current Flow

• You will see that the green Alternating Current waveform above is a Sine, or Sinusoidal Waveform. Most power systems attempt to provide pure sine waves for powering equipment.

Listen to a 220 Hertz Sine Wave

• There are many other types of Alternating Current (or A.C.) Waveforms other than the Sine Waveform
• One key to understanding electronics is learning how different Alternating Current Waveforms are used for different purposes, like powering things, controlling things, and making sounds.
• We'll show how all of these different Waveforms can be generated using a circuit or a small microcontroller like an Arduino.

Duty Cycle

• In an Alternating Current Waveform the ratio of "On" time to "Off" time (or positive time to negative time) is known as the Duty Cycle. Changing the Duty Cycle modifies the width of the pulses, and is also called Pulse Width Modulation. We'll be using Pulse Width Modulation (or PWM for short) later on, to control things like motors and dim lights.

  

Next

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Further (Links)

• All About Circuits
• Basic Concepts - MIT
• Basic Concepts - NYU