Digital vs. Analog

Discrete vs. Continuous Signals

Digital vs. Analog:

Discrete vs. Continuous Signals


Signals convey information and we are equipped to receive signals in various ways. We can receive auditory signals through our ears, visual signals through our eyes, signals of touch through nerves in our skin, etc. We can also store and convey information in different ways. We can write in a book, we can sound an alarm, and we can even make smoke signals. In the late eighteenth century, people realized they could use electrical devices to transmit information—they could use electrical signals. These electrical signals, coupled with the advances in technology over the past 200 years, have resulted in the “Information Age” in which we now live.

Electrical signals are classified as being of one of two types—either digital or analog. The two types of signals are depicted in Fig. 1, where the horizontal axis represents time and the vertical axis represents an electrical quantity such as a voltage or a current. Analog signals are ones that vary continuously in time. In contrast, as a function of time digital signals vary discontinuously from one level to another. The most common digital signal is binary, meaning the signal varies between only two different levels that we often refer to as HIGH and LOW. In fact, binary digital devices are so common that it is generally assumed that a “digital device” is a binary digital device unless explicitly specified otherwise.

Figure 1. Depiction of an analog (continuous) and a discrete (discontinuous) signal.

Another name for a level is state, so that a signal may be said to be in either a HIGH state or a LOW state. In addition to calling them HIGH and LOW, these binary states are sometimes called one and zero, on and off, or even true and false. Consistent with the use of true and false, you will often hear digital circuits referred to as logic circuits.

chipKIT™ boards are inherently binary digital devices, meaning that they use digital signals, even though (as we will see) they can also work with analog signals. These boards are equipped with a large number of electrical connectors known as pins. Sometimes these pins are used to obtain input (i.e., “read” an electrical signal) and sometimes they are used to generate output (i.e., “write” an electrical signal). We can configure the pins for input or output, and thus they are sometimes referred to as I/O pins .

To generate output, we (as the programmers of the boards) specify which pins should be HIGH, which should be LOW, and when the pins should be in these different states. One of the pins on the chipKIT boards is already associated with an LED. When the state of this pin is HIGH, the LED is on, and when it is LOW, the LED is off—because the chipKIT board is a digital device, the LED can only be in one of these two states.

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Important Points:

  • Analog signals vary continuously.
  • Digital signals only have discrete values.
  • chipKIT boards are binary digital devices where signals (or electrical levels/states) can take on only one of two values: HIGH or LOW.

  • Other product and company names mentioned herein are trademarks or trade names of their respective companies. © 2014 Digilent Inc. All rights reserved.