CHAPTER 11 ■ POWER ON!
Reading a Schematic
A schematic illustrates the logical connections between all of the parts (see Figure 11-1). Different types of
parts have different symbols. The symbols don’t look much like the real life object, but after you’ve seen a
few schematics, you’ll begin recognizing the symbols.
Each part is labeled with a letter and number. The letter relates to the type of part, like “R” for resistor.
This is a nice hint if you don’t recognize the schematic symbol.
Along with the letter, there’s a number that ensures that each part is labeled uniquely. If two resistors
appear in the schematic, they would be labeled R1 and R2. The number doesn’t necessarily suggest anything
about the location or value of the part; it simply gives it a distinctive name.
A bit of significant information about the part is usually displayed in the schematic along with the part
label. Referring to the schematic in Figure 11-1:
B1 – 9 V battery. Notice the location of the positive (+) and negative (-) indicators.
The symbol for a battery is two or more horizontal lines of different widths.R1 –1 kW resistor. “(BnBkRd)” is my shorthand for indicating that the resistor’s
color-code bands are brown, black, and red. The last band, tolerance, is usually
omitted as most resistors are gold (5%) or better nowadays. The symbol for a
resistor is a sharp, squiggly line.D1 – Red LED. I used the letter “D” because an LED is a diode. It would have
been perfectly acceptable to use “LED1.” In fact, “LED1” is preferable in circuits
that contain other types of diodes. Notice the symbol inside the circle is the arrow
crashing into a wall, just like on the multimeter dial. The two arrows coming out
of the circle represent light emissions.Center arrows – (five arrows in the middle) Sometimes arrows are drawn to
show the flow of electricity though a circuit. In this conventional depiction,
electricity comes out of the positive terminal of the battery, through the resistor,
through the LED, and into the other end of the battery.Figure 11-1. Power indicator circuit schematic