## [answered] Lab 5: 555 Clock Timer and DC Motor Speed Control Objective

?All I really need is Steps 5 and 6, and number 7 of the experiment questions. Please ASAP
Lab 5: 555 Clock Timer and DC Motor Speed Control Objectives

1. To simulate and operate an astable multivibrator.

2. To determine the timer frequency by mathematical calculations, by using a graph,

and by using test instruments.

3. To use an astable multivibrator in PWM generation and DC motor speed control.

Introduction

Clock signals are square-edged rectangular signals that continually change back and forth

between the two logic states. Many types of digital circuits require clock signals in order

to function. Clock signals are considered the heartbeat of microprocessor-based devices;

they provide the pulses necessary to time and control the proper sequencing of all events

throughout the computing system. A circuit that produces a continuous rectangular signal

is called an astable (free-running) multivibrator. An astable multivibrator, using a 555

timer chip, is shown in Figure 9-1. With only two resistors and a capacitor, the 555 IC

can produce a highly accurate rectangular signal.

Procedure

Step 1

Draw the circuit shown in Figure 9-1 in Multiim. Use the component values listed on the

first line of Table 9-1.

Background Information

The frequency of the timer depends on how rapidly the internal components of the 555 IC

turn on and off. This rate is determined by the values of the components connected

externally to the IC. The frequency of the output can be calculated by the following

formula: Figure 9-1 RA (k Ohm) RB (k Ohm) Table 9-1

C1(uF)

f (Hz)

Calculated 47 10 1 22 10 1 22 10 0.1 22 2.2 0.1 10 10 0.01 f (Hz)

Measured f(Hz) Chart

Value Step 2

Using the formula above, calculate f and record your answer in Table 9-1.

Step 3

Using the oscilloscope, measure fout (frequency out) at output pin 3 and record it in

Table 9-1.

Step 4

Repeat Steps 2 and 3 for the remaining values of RA, RB, and C1, given in the table.

Background Information?Frequency Chart

Figure 9-2 is a quick reference chart that provides a way of determining which

combination of external resistance and capacitance values generate a desired frequency.

To use the chart:

1. Select the desired frequency on the bottom horizontal line on the chart.

2. Follow this frequency line upward until it intersects an available capacitor value.

3. Read the combined resistance value for RA and 2RB from the nearest diagonal line. Figure 9-2 Step 4

Using the chart, find the astable multivibrator frequency for each of the RA, RB, and C1

values listed in Table 9-1. Enter the answer in the right-hand column (headed ?Chart

Values?). DC Motor Speed Control Using PWM and IC 555

PWM (Pulse Width Modulation) can be used to change the average of a DC voltage by

changing the ON/OFF ratio of a pulse signal. The ratio of the ON time to the period of

the pulse signal is Duty Cycle and is defined as follows: Duty Cycle= [(ON time)/(Period of the pulse)] x 100

Step 5

Use the figure 9-3 to draw and simulate 555 PWM generator in Multisim. The ratio of the

ON time to OFF time can be adjusted using the potentiometer in the circuit. Use

oscilloscope and measure the frequency of the output signal of the 555 IC. Draw the

waveform of 555 output and drain of the MOSFET transistor in the space below: 555 Output: ?............................................................................. Transistor Output: ?............................................................. Step 6

Use DVM and measure the voltage across the DC motor. Change the duty cycle and fill

out the following table. Duty Cycle

Motor voltage 5.00% Table 9-2

50.00% 75.00% 95.00% Figure 9-3 Experiment Questions

1. A circuit that produces a continuous rectangular signal is called a(n) ?.......

multivibrator.

2. The frequency of the 555 IC timer depends on what factors?

3. What activates the 555 IC timer?

4. What are clock signals used for?

5. Using the formula f = 1.44/(RA+2RB)C, determine the frequency of a 555 IC timer

when the component values are as follows:

RA = 2K Ohms, RB = 15K Ohms, C = 0.1microF, f =..............

6. Suppose a frequency of 1100Hz is desired and a 0.001microF capacitor is available.

Using the chart in Figure 9-2, determine the required combined values of RA and RB.

7- What is the purpose of diodes D1, D2 and D3 in figure 9-3?

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Sep 18, 2020

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