Schematic and Wiring Diagrams

In a schematic diagram, the interconnection of the components is shown, but the actual values of the components are not necessarily indicated. You might see a diagram of a two-transistor audio amplifier, for example, with resistors and capacitors and coils and transistors, but without any data concerning the values or ratings of the components. This is a schematic diagram, but not a true wiring diagram. It gives the scheme for the circuit, but you can’t wire the circuit and make it work, because there isn’t enough information.

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(A)
Schematic symbols for incandescent lamp
(B)
fixed capacitor
(C)
fixed inductor with air core
(D)
fixed inductor with laminated-iron core
(E)
chassis ground
(F)
earth ground
(G)
signal generator or source of alternating current
(H)
pair of terminals
(I)
specialized component or device

Suppose you want to build the circuit. You go to an electronics store to get the parts. What values of resistors should you buy? How about capacitors? What type of transistor will work best? Do you need to wind the coils yourself, or can you get ready-made coils? Are there test points or other special terminals that should be installed for the benefit of the technicians who might have to repair the amplifier? How many watts should the potentiometers be able to handle? All these things are indicated in a wiring diagram. You might have seen this kind of diagram in the back of the instruction manual for a hi-fi amplifier, a stereo tuner, or a television set. Wiring diagrams are especially useful when you want to build, modify, or repair an electronic device.