Читать книгу Electronics All-in-One For Dummies - Lowe Doug, Doug Lowe - Страница 72

One important symbol that isn’t shown in Table 5-1 is the symbol for an IC (integrated circuit). ICs are small assemblies that usually have multiple leads, called pins, which connect to various parts of the circuit contained within the assembly. Some ICs have as few as six or eight pins; others have dozens or even hundreds. These pins are numbered, beginning with pin 1. Each pin in an IC has a distinct purpose, so connecting to the correct pins in your circuit is vital to the circuit’s proper operation. If you connect to the wrong pins, your circuit won’t work, and you may damage the IC.

The most common way to depict an integrated circuit in a schematic diagram is as a simple rectangle with leads coming out of it to depict the various pins. The arrangement of the pins in the schematic diagram doesn’t necessarily correspond to the physical arrangement of pins on the IC itself. Instead, the pins are positioned to provide for the simplest circuit paths in the diagram. The pins in the diagram are numbered to indicate the correct pin to use.

For example, Figure 5-8 shows a schematic diagram that uses a popular IC called a 555 timer IC to make an LED flash. The 555 has eight pins, and you can see that the schematic calls for connections on all eight. However, the pins in the diagram are arranged in a manner that simplifies the connections to be made to the pins. In an actual 555 IC, the pins are arranged in numerical order on either side of the IC, with pins 1 through 4 on one side and pins 5 through 8 on the other side.

FIGURE 5-8: A circuit that uses an integrated circuit.

Don’t worry about any of the details of the operation of this circuit. You learn how it works in Book 3, Chapter 2. My only purpose for including it here is so you can see how integrated circuits are depicted in a schematic diagram.