By John Sanger

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Value designations also are given on the diagram. If you would like to put this circuit together, you can find the parts at most electronics stores. The parts list is shown in Table 3 - 2 . Once you have connected all the components, you will have a device with two LEDs that alternately blink on and off. House the components in an attractive box. Paste your business card on the front and drill small holes (the same size as the LEDs you are using) on each side of the card. Insert and glue the LEDs into the holes so they stick out past your card.

SWITCHES A switch is a device that makes (connects) and/or breaks (disconnects) an electrical connection. It selectively allows current to pass. Single-Pole Switches Switches that make contact in only one position, such as common light switches, are called single-pole, single-throw (SPST) switches. The schematic symbol for this type of switch is shown in Figure 2 - 2 0 . As 28 BASIC ALARM ELECTRONICS Figure 2-20. A single-pole, single-throw (SPST) switch is an on-off type of switch. Figure 2—21.

Pythagorean Theorem: A theorem of plane geometry which states that for a right triangle, with sides of lengths a, b, and c, where c is the side opposite the right angle, it is always true that a2 + b2 = c2. Reflection Law: The angle of incidence is equal to the angle of reflection. Speed of Light: The velocity of light is approximately 180,000 miles per second. Speed of Sound: The speed of sound is approximately 1,129 feet per second in air and 4,800 feet per second in water. FORMULAS AND CONVERSIONS As useful as scientific laws are, sometimes high school level mathemat­ ics, algebra, and geometry help alarm installers do their jobs.