Chapter 12 Electronics

Objectives Identify the values of resistors based on the resistor color code. Using capacitors with resistors for timing functions. Use of common electronic components including resistors, capacitors, diodes, and transistors.

Resistors A resistor resists the flow of electricity. Restricting flow can be useful for protecting components in a circuit. The unit of resistance is the ohm (Ω). The amount of resistance offered by a resistor can be determined by reading 4 or 5 color bands on the resistor and then calculating the resistance (see fig 12-1, page 279). On a 4 band resistor, the first two bands represent a numeric value, the third band is a multiplier, and the fourth band is the tolerance. On a 5 band resistor, the first 3 bands represent digits, the 4th band is a multiplier, and the 5th band is the tolerance. Any resistor that does not have a tolerance band, has a tolerance of +- 20%. Before measuring resistance in a circuit with a multimeter make sure the circuit is de-energized(fig 12-2, page 280). Variable resistors perform the same function as fixed resistors, except the resistance value can be varied. (fig 12-3, page 281 Dimmer switch)

Capacitors A capacitor has the ability to store electrical charge. There are several types of capacitors, but two of the most common are ceramic disk and electrolytic (fig 12-4, page 283). The unit of capacitance is known as the farad(F). Capacitors are usually rated in micro farads (µF = 10-6 F).

Diodes A standard diode allows for one way flow of electricity. A band on the diode indicates the cathode (negative terminal) of the diode (fig 12-6, page 284). The schematic indicates the cathode with a line and the anode (positive terminal) with a triangle. Rectifier circuits: A diode is useful for converting AC (alternating current) into DC (direct current). Diodes can be tested by using a multimeter or continuity tester (diode check). Zener Diodes are used in voltage regulation circuits. Light Emitting Diodes (LEDs) are used in lighting.

Transistors Transistors are solid state (no moving parts) switching devices. A bipolar transistor has 3 junction points: an emitter, a base, and a collector. Field effect transistors (FETs) are another type of transistor that can carry much more current than a bipolar transistor. It has 3 terminals: a gate, a source, and a drain. Metal oxide semiconductor FETs (MOSFETs) are often used as switches.

Integrated Circuits (ICs) An integrated circuit (IC) is a collection of electronic circuits installed in a ceramic or plastic housing (fig 12-13, page 288). The pins allow the IC to be installed in a base called a socket so the IC can be connected to other components in a circuit. A dot or notch usually identifies pin 1 on an IC. A pin out shows all the pins on a given IC and may indicate their purpose (fig 12-14, page 289). Common applications of ICs include counting functions, timing functions, and logic functions. A TTL (transistor transistor logic) IC works on low voltage (5V). TTL ICs usually begin with a number 74 such as 7448. A CMOS (complementary metal oxide semiconductor) IC works with voltages up to 18V and draws very little current. However CMOS ICs are easily damaged by static electricity and must be handled and stored with care. CMOS ICs begin with the number 4, like 4046. CMOS ICs and TTL ICs are incompatible with each other – cannot replace one with the other.

Fuses, Circuit Boards, Schematic diagrams, & Troubleshooting Fuses and circuit breakers protect electronic circuits from excessive current flow. Circuit boards serve as a base for mounting components and serve as a part of the circuitry (fig 12-15, page 290). Tiny copper paths on the circuit board make many of the connections between electronic components. Schematic diagrams allow for the construction and troubleshooting of electronic circuitry. Troubleshooting: It is important to perform troubleshooting in a systematic manner. This means checking only one component at a time , verifying it is functioning properly, and then moving to the next component.

Summary A resistor resists the flow of electricity. The unit of resistance is the ohm (Ω). Variable resistors perform the same function as fixed resistors, except the resistance value can be varied. A capacitor has the ability to store electrical charge. The unit of capacitance is known as the farad(F). A standard diode allows for one way flow of electricity. A diode is useful for converting AC (alternating current) into DC (direct current). Zener Diodes are used in voltage regulation circuits. Light Emitting Diodes (LEDs) are used in lighting. Transistors are solid state switching devices. An integrated circuit (IC) is a collection of electronic circuits installed in a ceramic or plastic housing. Common applications of ICs include counting functions, timing functions, and logic functions. A TTL (transistor transistor logic) IC works on low voltage (5V). A CMOS (complementary metal oxide semiconductor) IC works with voltages up to 18V and draws very little current. However CMOS ICs are easily damaged by static electricity and must be handled and stored with care. Troubleshooting: It is important to perform troubleshooting in a systematic manner. This means checking only one component at a time , verifying it is functioning properly, and then moving to the next component.

Home Work 1. What is one use of a diode? 2. Give one advantage and one disadvantage of a CMOS IC.