A circuit diagram (electrical diagram, elementary diagram, electronic schematic) is a graphical representation of an electrical circuit. A pictorial circuit diagram uses simple images of components, while a schematic diagram shows the components and interconnections of the circuit using standardized symbolic representations. The presentation of the interconnections between circuit components in the schematic diagram does not necessarily correspond to the physical arrangements in the finished device. Unlike a block diagram or layout diagram, a circuit diagram shows the actual electrical connections. A drawing meant to depict the physical arrangement of the wires and the components they connect is called artwork or layout, physical design, or wiring diagram. Circuit diagrams are used for the design (circuit design), construction (such as PCB layout), and maintenance of electrical and electronic equipment. In computer science, circuit diagrams are useful when visualizing expressions using Boolean algebra.

Electro-System Co., Ltd. (エレクトロ・システム株式会社, Erekutoro Shisutemu Kabushiki Gaisha), commonly called to as EleSys, is a Japanese electronics company headofficed in Sakuradai Nerima, Tokyo, Japan. The company is one of the leading companies of one-top services for electronic design or products mostly in the non-consumer or professional markets. Also it sells and develops software for CAD, interface (USB or WiFi) or simulator.