Circuit diagrams can be classified into four types: schematic diagrams, wiring diagrams, basic diagrams, and design diagrams. Schematic diagrams depict the functional components of an electric circuit and their interconnections. Wiring diagrams (for connections and junctions) show the arrangement of circuit components and of connecting wires.
The devices in an electronic circuit are classified as being either passive or active. The passive devices change signal energy, as is done dynamically by capacitors and statically by transformers, or absorb signal energy, as occurs in resistors, which also act to convert voltages to currents and vice versa. The active devices, such as batteries, transistors, operational amplifiers, and vacuum tubes, can supply signal energy to the circuit and in many cases amplify signal energy by transforming power supply energy into signal energy.