# Appendix III: Conversion of Analog and Digital Information

Today, the term digital is a word we hear frequently because digital circuits are becoming so widely used in computation, robotics, medical science and technology, communication, transportation, etc. Digital electronics developed from the principle that the circuitry of a transistor could be designed and fabricated easily to have an output of one or two voltage levels, based on its input voltage.

A transistor is a semiconductor used in circuits that acts as a high-speed switch or to provide amplification. Transistors have taken the place of vacuum tubes.

The two voltage levels are usually 5 volts (high) and 0 volts (low); the levels can be represented by 1 and 0. The binary numbering system (base-2 numbering system) is one of the numbering systems used in digital electronics. A digital value is represented by a combination of on and off voltage levels written as a string of 1s and 0s. When applying technology, we are constantly dealing with quantities that must be measured, monitored, recorded, or manipulated. These values must be able to be represented efficiently and accurately. Two ways of representing these values are analog and digital.

In analog representation, a quantity is represented as on a voltage meter movement or current; the representation is proportional to the value of the quantity. One example is a column of mercury in a thermometer. The height of the mercury represents the temperature, and its height changes as the temperature rises or falls. Another example is an audio microphone, in which sound waves from the voice alter as they impinge on the microphone; these variations cause output voltage to vary proportionally. The important point to remember about analog representation is that the output represented can have a continuous range of values, i.e., the temperature in a room can have any value ranging from say 60° F to 85° F, and the height of the mercury would respond accordingly.

Digital, on the other hand, utilizes circuitry whereby quantities are represented not proportionally, but by symbols called digits. An example is the digital watch, which displays the time in the form of decimal digits. Even though the time of the day is changing continuously, the digital watch changes in steps or increments of a minute, or second, or hour. Put another way, an analog value is continuous, but a digital value is discrete; because of this difference, when reading a digital value there is no uncertainty but the value of an analog quantity depends on how the person reads it and the value may be different from that which the next person reads.

Consider the following examples and indicate whether they are analog or digital:

1. ten-position switch
2. water flowing out of a meter
3. temperature of a room
4. grains of sand on a beach
5. speedometer on an automobile

Answers: A. digital, B. analog, C. analog, D. digital (the number of grains is a discrete value), E. analog if it’s the needle type, and digital if it’s the numerical readout type. Digital systems are usually electronic, but they can be mechanical, pneumatic, or magnetic. Examples are digital computers and the telephone system, the world’s largest digital system.