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 car 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 domestic 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

• When looking at a Waveform plot, like the one below, you will see the magitude (either Current or Voltage) on the Y-Axis and the passage of Time on the X-Axis

• 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 using micro-controllers like the Arduino.

  

• In the War of Currents Thomas Edison and Nikola Tesla (and their proxies - Westighouse and General Electric) waged commercial war to see if America would have DC (Edison) or AC (Tesla) electricity wired to every home. As you likely know, AC won the war, as DC is more lossy to distribute over long distances. Tesla was an amazing engineer, as he would hold complex designs and simulations in his head before ever putting them down on paper.

Next

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Further (Links)

• Sparkfun AC-DC
• All About Circuits
• Basic Concepts - MIT
• Basic Concepts - NYU