Читать книгу Electronics All-in-One For Dummies - Lowe Doug, Doug Lowe - Страница 71

A symbol alone is not usually enough information to completely identify an electronic component in a schematic diagram. Further information is usually included with text that’s placed adjacent to the symbol, as shown in Figure 5-7. This additional information usually includes the following:

FIGURE 5-7: A schematic diagram with parts labeled.

 Reference identifier: Each component is usually labeled with a letter that designates the type of component followed by a number that helps identify each component of the same type. For example, if a circuit has four resistors, the resistors are identified as R1, R2, R3, and R4. The most commonly used letters are shown in Table 5-2.

 Value or part number: For components such as resistors and capacitors, the value is given in ohms (for resistors) and microfarads (for capacitors). Thus, a 470 Ω resistor would have the number 470 next to it, and a 100 μF capacitor would have the number 100 next to it.The letters k and M are used to denote thousands and millions. For example, a 10,000 Ω resistor is identified as 10k in a schematic.Components such as diodes, transistors, and integrated circuits don’t have values; instead, they have manufacturer’s part numbers. Thus, you might find a part number such as 1N4001 (for a diode), 2N2222 (for a transistor), or 555 (for an integrated circuit, IC) next to one of these components.In some cases, the value or part number is omitted from the schematic diagram itself and instead included in a separate parts list that identifies the value or part number of each referenced part that appears in the schematic. Then, to find the value or part number of a particular component, you look up the component by its reference identifier in the parts list.

TABLE 5-2 Commonly Used Reference Identifiers

Letter	Meaning
R	Resistor
C	Capacitor
L	Inductor
D	Diode
LED	Light-emitting diode
Q	Transistor
SW	Switch
IC	Integrated circuit