Switches


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Switches Essay, Research Paper

2.When

the start button is pushed the switch closes and the voltage of the ?set? input

goes high causing Q to go low. However when the ?reset? input goes high, Q will

also go low until the stop switch is pressed forcing it to go high.1.The

555 oscillator forms the basic timing process of eth watch/stopwatch central

circuitry. The frequency of eth oscillation is controlled by C1 and R1. F =??????????? 1 ???????????????? C 1 x R 1 F = 1 The output of the oscillator is fed into the clock input of eth 40173.The

4017 is a decade counter. When the reset pin is high the clock pulses from the

555 chip are counted. At the first count the Q output goes high and the LED at

pin 10 controlled by TR1 goes on. On the second clock pulse, pin 5 goes high

and the second red LED controlled by TR2 goes on. At pin 9 on the third clock

pulse the buzzer controlled by TR3 and the stopwatch simultaneously go on. When

pin 11 goes high on the fourth count the bistable is reset and the counter

reset goes low, stopping the counter. However including the diode prevents JFET

being turned off allowing the stopwatch to continue to count until the stop

switch is pushed.4,5,6.When

the voltage in pin 5,9 and 10 goes high (+5V), the transistors conduct the

LED?s and buzzer are active. The 10K resistors, R1, 2 and3 limit the current

that flows into the base of the transistor and further resistors (4 and 5)

whose job it is to limit the current flowing through the LED?s.The

values I choose limit the base current to: ????? 5 – 0.6 10K?? ??? =0.4mA And the LED count to:????????????? 5 330

=

0.015mAThe

power dissipation is TR1, TR2 is:

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