Chapter 6 Electromechan e r m m a ni cal a S Sy s st e e em s s 161 Copyright Goodheart-Willcox Co., Inc. Copyright Goodheart-Willcox Co., Inc. Activity 6-9 Digital Timers Objectives Digital timers employ a time base generator (oscillator), a counter, and a load- driver circuit. The counter circuit frequently has several output terminals that permit selection of time ranges. Control ranges of 1T, 2T, 4T, 8T, 16T, and 32T are typical. Each output is rated in terms of the time base (T) of the generator circuit. In this activity, you will employ the SE/NE555 timer IC as the time base generator of a simple digital timing system. The output of the generator will be counted and divided to some extent by the range of the system. Through this cir- cuit investigation, you will see and work with the basic parts of a simple digital timing system. Commercially designed timers of this type are usually housed in an enclosure that does not permit access to component parts. These timers gener- ally do not employ moving parts and are all solid state. The timing period is very accurate, and it usually ranges from microseconds to hours. Again, this type of f device is being studied to represent the various types of timing control applica- tions that might be used with robotic systems. Equipment and Materials • SE/NE555 IC. • 200 kΩ, 1/8 W resistors (2). • 390 Ω, 1/8 W resistor. • Light-emitting diode. • 4 μF, 25V dc capacitor. • 0.01 μF, 100V capacitor. • 50 μF, 25V capacitor. • SPST toggle switches or pushbuttons. • SN7490 IC. • Circuit mounting board.