====== I. Overview ======
===== - Digital and analog quantities =====
Analog quantities have continuous values. Digital quantities have a discrete set of values.

The temperature of my body does not suddenly change from 99°F to 97°F. The change is gradual, analog. We can quantize the graph below by sampling the temperature curve at some discrete points in time. This sampled-value representation is not digital in itself, but it can be digitized easily. Quantization comes before digitization.

{{https://upload.wikimedia.org/wikipedia/commons/0/05/Body_Temp_Variation.png?nolink|}}

Digital is better than analog in many cases. Digital data can be stored, processed and transmitted more easily. Digitized music takes less space. **Noise** affects analog data much more.

A microphone-speaker system is a pure analog system. Sound waves move capacitor plates creating a voltage pattern which is amplified and supplied to a speaker that converts the electrical signal back to mechanical waves. Everything in this process is analog, continuous.

A CD (compact disk) player has both digital and analog circuits. Music is stored in the disk digitally. A laser-diode optical system reads the data and supply it to a digital-to-analog converter (**DAC**). An analog-to-digital converter (**ADC**) was used while recording the music.

Both digital and analog systems are needed in the interdisciplinary field of **mechatronics**.

===== - Binary digits, logic levels and waveforms =====
In digital circuits and systems there are only **TWO** possible states represented by two different voltage levels: HIGH and LOW. They could be represented by two current levels or bits and bumps in a CD or DVD.

States are called **codes**. A two-state number system is called **binary**, it has two digits: 0 and 1. A **digit** is called a **bit** (short for ‘binary digit’).

Positive logic: HIGH = 1 and LOW = 0. Negative logic is the opposite.


===== - Basic logic functions =====
===== - Combinational and sequential logic functions =====
===== - Programmable logic =====
===== - Fixed-function logic devices =====
===== - Oscilloscope =====