Transistors and Electrical Signals
Transistors are commonly used to amplify signals. An electrical signal is the pattern over time of an electrical current. Often, the way an electrical signal changes its shape conveys information about something physical, such as the intensity of light, heat, or sound, or the position of an object, such as the diaphragm in a microphone or the shaft of a motor.
Think of an electrical signal as a code, somewhat like Morse code, sending and receiving secret messages that you can figure out — if you know the key.
An analog electrical signal, or simply analog signal, is so named because it is an analog, or one-to-one mapping, of the physical quantity it represents. For instance, when a sound studio records a song, fluctuations in air pressure (that’s what sound is) move the diaphragm of a microphone, which produces corresponding variations in electrical current. That fluctuating current is a representation of the original sound, or an audio signal.
Digital systems, like computers, can’t handle continuous analog signals, so electrical signals must be converted into digital format before entering the depths of a digital system. Digital format is just another coding scheme, one that uses only the binary values 1 and 0 to represent information, much like Morse code uses dots and dashes. A digital signal is created by sampling the value of an analog signal at regular intervals in time and converting each value into a string of bits, or binary digits.