Basic Alarm Electronics. Toolbox Guides for Security by John Sanger

By John Sanger

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Schematic symbols for rotary switches vary depending on the number of poles and positions, but they look similar to the one shown in Figure 2—24. Two varieties of rotary switches help you do the precise job you want to do. One type, the make-before-break switch, maintains the Figure 2-24. A rotary switch allows you to control numerous circuits. 30 BASIC ALARM ELECTRONICS Figure 2-25. A spring-loaded momentary-contact switch makes or breaks a circuit only while the switch's lever or button is thrown or pushed.

The larger the wire, the greater its cost. You will know what size wire you need if you use Ohm's law and will not have to guess. VARIATIONS OF THE LAW If you recall your high school algebra, you remember that equations can be written different ways. Therefore, the basic equation, I = E/R, also can be written as: R = E/L Resistance can be determined if you know or can measure voltage and current. You can use a multi-meter to measure a circuit's resistance. Ohm's law gives you an idea of what the resistance should be before you measure it.

First connection until the second connection is made. The other type, the break-before-make switch, does just the opposite. Momentary-Contact Switches If you need to make or break a circuit connection briefly, then return the circuit to its original condition, a momentary-contact switch can be used. This type of switch allows you to operate it without having to move the lever or button of a latching switch from one position to another. Normally open spring-loaded, momentary-contact switches often are used as panic buttons in alarm systems.

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