Experiment EB2: IC Multivibrator Circuitsfoe.mmu.edu.my/lab/lab sheet/TRIM2/BETA/EEE1026-EB1,EB2... · Web viewExperiment EB2: IC Multivibrator Circuits Learning Outcomes LO4: Analyze

EEE1026 Electronics II: Experiment Instruction

Experiment EB2: IC Multivibrator Circuits

Learning Outcomes

LO4: Analyze the operation of JFET, MOSFET and BJT amplifiers and switching circuits.

1.0 Objectives To measure the frequency and duty cycle of an astable 555 timerTo measure the pulse width and duty cycle of a monostable 555 timerTo measure the frequency and duty cycle of a voltage-controlled oscillator

2.0 ApparatusEquipment required Components requiredPower Supply – 1 Timer IC 555 – 2Oscilloscope – 1 Resistor 10k (1/4W) – 2Multimeter – 1 Resistor 100k (1/4W) – 1Breadboard – 1 Resistor 33k (1/4W) – 1Function Generator – 1 Resistor 68k (1/4W) – 1

Resistor 47k (1/4W) – 1Resistor 1k (1/4W) – 2Mylar Capacitor 0.01F – 4Potentiometer (1k) – 1

3.0 Introduction

Multivibrators are circuits that are designed to have zero, one, or two stable output states. The 555 timer is one of the most popular general purpose IC multivibrators. It can be used in a variety of applications requiring accurate time delays, oscillation, and pulse conditioning. Signetics Corporation first introduced it as SE555 timer, which is an 8-pin IC that can be connected with external components for either astable or monostable operation. Figure 1 shows the simplified block diagram of a 555 timer. The circuit’s name is derived from the use of an internal voltage divider between VCC and ground using three 5k resistors. This divider chain is used to set a pair of reference voltages for two comparators that drive the set and reset inputs of an R-S flip-flop.

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Figure 1: Block diagram of 555 Timer

Refer to Figure 1, a logic high voltage (+V0) applied to the set S input and a logic low (0V) to

the reset R input forces the output Q to high (VCC) and Q̄ low (0V). This is referred to as the set condition of the flip-flop. A high reset R and low set S causes the output to switch to a low

Q and a highQ̄ . This is referred to as the reset condition of the flip-flop. The circuit latches in either of the two states. In other words, a high S input sets Q to high; a high R input resets Q to low. Output Q remains in a given state until triggered into the opposite state.

The comparators are simply Op-amps. Note that the upper comparator has a threshold input (pin 6) and a control input (pin 5). In most applications, the control input is not used, so that the control voltage equals +2VCC/3. However, applying an external voltage to this pin provides some control over the reference voltages for both comparators. When the voltage of pin 6 exceeds the control voltage, the high output from the Op-amp will set the flip-flop. The high Q output from the flip-flop will turn on transistor Q1 and discharge the external timing capacitor connected to pin 7. The complementary signal (logic low) of the flip-flop goes to pin 3, the output.

When the external reset (pin 4) is grounded, it inhibits the device. This ON-OFF feature is useful sometimes. In most applications, however, the external reset is not used and pin 4 is tied directly to the supply voltage. The inverting input of the lower comparator is called the trigger (pin 2) and its noninverting input has a fixed voltage of +VCC/3 developed by the three 5k voltage divider. When the trigger input voltage is slightly less than +VCC/3, the Op-amp output goes high and resets the flip-flop. Lastly, pin 1 is the chip ground, while pin 8 is the power supply pin. The 555 timer will work with any supply voltage between 4.5 and 16V.

Monostable Operation

Figure 2a shows the 555 timer connected for monostable (one-shot) operation. It produces a single, fixed voltage, output pulse each time a trigger pulse is applied to pin 2 (Figure 2b).

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8

Q1

RESET

+VCC

THRESHOLDCONTROL

GROUND

TRIGGER

DISCHARGE

OUTPUT3

7

2

5

6

41

5k

5k

5k

Q

_QR

S+_

+_


(a)

(b)Figure 2: (a) Monostable operation; (b) ideal waveforms

The trigger input is a narrow pulse with a quiescent value of +VCC. When the trigger input is slightly less than +VCC/3, the lower Op-amp has a high output and resets the flip-flop. This cuts off the transistor, allowing the capacitor to start charging up. As the capacitor charges, the voltage at pin 6 increases. Eventually, the voltage becomes slightly greater than the control voltage (+2VCC/3). The output of the upper Op-amp then goes high, forcing the RS flip-flop output to be set. As soon as Q goes high, it turns on the transistor and this quickly discharges the capacitor. As a result, we get a triangular pulse at pin 6 & 7.

The capacitor C is charged through resistance R. For a larger RC time constant, the capacitor will take longer time to charge to +2VCC/3. In other words, the RC time constant controls the width of the output pulse. Solving the exponential equation for capacitor voltage gives the formula for its pulse width as

W =1. 1 RC (1)

Astable OperationFigure 3a shows the 555 timer connected for astable or free-running operation. The output is a square-wave signal. When Q is low, the transistor is cut off and the capacitor is charged

through (RA+RB ). Because of this, the charging time constant is( RA+RB)C . When the voltage at pin 6 is slightly greater than +2VCC/3, the upper Op-amp has a high output and this sets the flip-flop. With Q high, it turns on the transistor and grounds pin 7. Now the capacitor

discharges throughRB . The discharging time constant isRBC . When the capacitor voltage drops slightly below +VCC/3, the lower Op-amp has a high output and this resets the flip-flop.

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5k

5k

5k

R

6

7 8

32

1

C

TRIGGERVout

+VCC

Q

_QR

S+_

+_

(pin 3)

0

(pin 6 & 7)

(pin 2)

+VCC

+2VCC/3

+VCC

0

0


(a)

(b)Figure 3: (a) Astable operation; (b) ideal waveforms

Figure 3b illustrates the waveforms; the timing capacitor has an exponentially rising and

falling voltage and the output of Q̄ is a rectangular wave. Since the charging time constant is longer than the discharging time constant, the output is not symmetrical; the high state lasts longer than the low state. To specify how unsymmetrical the output is, we can define duty cycle as

D=WT

×100 %(2)

Depending on the resistances RA andRB , the duty cycle is between 50 and 100 percent. The mathematical solutions of the charging and discharging equations give the following formulas. The output frequency is

f = 1.44( RA+2 RB)C (3)

and the duty cycle is

D=RA+RB

RA+2 RB×100 %

(4)

If RA is much smaller thanRB , the duty cycle approaches 50 percent.

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RB

5k

5k

5k

RA

6

7

8

32

1

CVout

+VCC

Q

_QR

S+_

+_

(pin 3)

(pin 2 & pin6)

+VCC

TW

+VCC/3

+2VCC/3

0


Voltage-Controlled Oscillator (Pulse Position Modulator)The free-running multivibrator can be modified to become a voltage-controlled oscillator (VCO). Recall that pin 5 (control) is connected to the inverting input of the upper Op-amp. Normally, the control voltage is +2VCC/3 because of the internal voltage divider. In VCO, however, the voltage from an external potentiometer overrides the internal voltage. In other words, by adjusting the potentiometer, we can change the control voltage level. If we increase Vcontrol, the capacitor will take a longer time to charge and discharge; therefore, the frequency decreases. As a result, we can change the frequency of the circuit by varying the control voltage.

4.0 ProceduresA. Astable 555 Timer1. Refer to the 555 timer circuit shown in Figure 4-1. The schematic diagram does not show

the op-amps, flip-flop, and other components inside the 555 timer, but only the pins and external components.

2. Notice that pin 5 (control) is bypassed to ground through a small capacitor, typically 0.01F. This provides some noise filtering for the control voltage.

3. Based on equations (3) and (4), calculate and record the frequencies (fcal) and duty cycles (Dcal) for the resistances listed in Table 4-1 in Appendix D2.

4. Connect the circuit of Figure 4-1 on a breadboard with RA = 10k and RB = 10k. Measure and record the supply voltage VCC(meas) with a multimeter.

5. Using an oscilloscope (set CH1 and CH2 to DC coupling and trigger source to CH1), and connect the probes at pin 3 (CH1) and pin 6 (CH2), measure the waveforms Vout (at CH1) and Vpin-6 (at CH2). If the circuit is functioning properly, these waveforms will be similar to those in Figure 3(b).

6. Align the ground levels of CH1 and CH2 as indicated on Graph 4-1 in Appendix D2. Adjust Volts/div and Time/div to display the waveforms on the screen as big as possible with one to two cycles. Sketch Vout and Vpin-6 waveforms on Graph 4-1.

7. Measure and record the period, T and the high portion of the pulse width, W. Determine the frequency f and duty cycle D from the measurement results.

8. Repeat steps 5 through 7 for the other resistances of Table 4-1. 9. For RA = 100 k and RB = 10 k case, measure and record the maximum and minimum

voltage levels of Vout and Vpin 6 waveforms.10. Ask the instructor to check all of your results. You must show the last oscilloscope

waveforms to the instructor.

SE/NE555

Figure 4-1: Astable 555 Timer Circuit (TOP VIEW)

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Vout

C2=0.01FC1=0.01F

5RB

RA

12

555Timer

7

6

84

3

VCC=+5V

6

5

7

8

3

4

2

1


B. Monostable 555 Timer*Do not remove the circuit from the previous part. The connection of IC U1 is similar with Part A.

1. IC U2 of Figure 4-2 is a 555 timer connected for monostable operation. Calculate the pulse width for each resistance value R listed in Table 4-2. Record the results under Wcal.

2. IC U1 of Figure 4-2 is the astable multivibrator circuit of Part A. It is used here to provide the trigger input to the monostable circuit (U2).

3. Connect the circuit of Figure 4-2 with resistance R = 33k. Measure and record VCC(meas).4. Using an oscilloscope, measure the waveforms at pin 2, Vpin2 (at CH1) and pin 3, Vout (at

CH2) of the monostable circuit (U2). Set CH1 and CH2 to DC input coupling and trigger source to CH1. Align the ground levels of CH1 and CH2 as indicated on Graph 4-4. Set Time/div to display the waveforms with one to two cycles on the screen. Set Volt/div to display the waveforms as big as possible but not overlapping. Sketch the waveforms.

5. Measure and record the pulse width, W, at the output of U2.6. Repeat steps 4 to 5 for the other resistances R in Table 4-2.7. For R = 68 k case, connect CH2 to pin 6, measure and record the maximum and

minimum voltage levels of pin 6 waveform.8. Ask the instructor to check all of your results. You must show the last oscilloscope


Figure 4-2: Monostable 555 Timer Circuit

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0.01F0.01F

510k

100k

12

U1555Timer

7

6

843 Vout

0.01F

0.01F

5

R

12

U2555Timer

7

6

843

VCC=+5V


C. Voltage-Controlled Oscillator

1. Connect the voltage-controlled oscillator (VCO) of Figure 4-3 (refer to Appendix A for the potentiometer legs). Measure and record VCC(meas).

2. Measure the output, Vout (CH1) and pin 6, Vpin 6 (CH2) waveforms with an oscilloscope. Set CH1 and CH2 to DC input coupling and trigger source to CH1. Align the channel ground levels as indicated on Graph 4-5. Adjust Volts/div to display the waveforms on the screen as big as possible.

3. Vary the 1-k potentiometer and notice the changes in the waveforms. Adjust Time/div if necessary.

4. Turn the potentiometer to get the minimum frequency. Adjust Time/div to display the waveforms with one to two cycles on the screen. Sketch Vout and Vpin 6 waveforms.

5. Measure and record T, W, Vpin 6 (max) and Vpin 6 (min). Measure and record the DC voltage at pin 5, Vpin 5 with a multimeter. Calculate the frequency and duty cycle.

6. Turn the potentiometer to get the maximum frequency. Repeat steps 4 and 5. 7. Ask the instructor to check all of your results. You must show the last oscilloscope


Figure 4-3: Voltage-Controlled Oscillator Circuit

Report Submission

You must obtain the signature of the Instructor after completing each section of the experiment. Submit your report together with the Rubric assessment form to your Lab Instructor, immediately after your experiment session.

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B

AVar

1k

1kVout

C1=0.01F

5100k

10k

12

555Timer

7

6

84

3

1k

VCC=+5V

The Resistor color code chart

ABC

AB x 10C pF

.abc

0.abc F

Capacitance

Potentiometer

A Var B


APPENDIX A

Log Scale The distance in a decade of the log scale in the figure below is x mm. Since log 101 = 0, it is used as a refernce point (0 mm) in the linear scale. Then, the reading 10 is located at x mm and the reading 0.1 is located at –x mm. For a reading F, it is located at [1og10(F)]*x mm. E.g.: Reading 0.25 is located at [1og10(0.25)]*x mm = -0.602x mmReading 2.5 is loacted at [1og10(2.5)]*x mm = 0.398x mmReading 25 is located at [1og10(25)]*x mm = 1.398x mm (not shown in the figure)Reading 250 is located at [1og10(250)]*x mm = 2.398x mm (not shown)

Conversely, a point at z mm location is read as 10z/ x.

E.g.: -0.3x mm is read as 10(-0.3x/x)

= 0.5010.6x mm is read as 10(0.6x/x)

= 3.981.5x mm is read as 10(1.5x/x)

= 31.6 (not shown)2.7x mm is read as 10(2.7x/x)

= 501 (not shown)

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8764

0.90.8

0.70.60.4

-0.3x

0.501 3.98

0.6x-0.602x 0.398x

2.50.25

Log scale (unit)

Linear scale (mm)

x0-x

10 5 3210.50.30.20.1 9

EEE1026 Electronics II

Internal connections

Internal connections

0.1 F

General mistakes:The legs of the resistors and the transistor are shorted by the breadboard internal connections.

8 7 6 5

1 2 3 4

555

0VGND

+VCC

Horizontally connectedHorizontally connected

Vertically connected

Vertically connected

Appendix B: Breadboard Internal Connections

EEE1026 Electronics II

Appendix D2Experiment EB2: IC Multivibrator Circuits

Lab Report(Together with Rubric form, Submit your report on the same day immediately after the

experiment)

Name: ________________________ Student I.D.: _______________ Date: __________

Majoring: ____________________ Group: ____________ Table No.: ____________

4. Astable 555 Timer

VCC(meas) = _________V

Table 4-1: Astable Operation for various RA and RB

RA (k) RB (k) f cal Dcal T W f D10 1010 100100 10

For RA = 100 k, RB = 10 k case (Step 9):

Vout (max) = ______ V VCC(meas) – Vout (max) = ______ V

Vout (min) = ______ V

Vpin 6 (max) = ______ V Vpin 6 (max) / VCC(meas) = ______

Vpin 6 (min) = ______ V Vpin 6 (min) / VCC(meas) = ______

Graph 4-1: Astable Operation for RA = 10 k, RB = 10 k

Time base : ______ s/div, CH1 (Vout) : ______ V/div, CH2 (Vpin 6) : ______ V/div

CH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 ground

EEN1026 Electronics II Experiment EB2





* Note: Ask your instructor to verify your results before you proceed to Part B.

Signature: ______________ Time: ___________ Remarks _________________

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CH1 & CH2 ground

CH1 & CH2 ground

CH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 ground

CH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 ground


B. Monostable 555 Timer

VCC(meas) = _________V

Table 4-2: Monostable Operation for various R

R (k) Wcal W334768

For R = 68 k case (Step 7):

Vpin 6 (max) = ______ V Vpin 6 (max) / VCC(meas) = ______

Vpin 6 (min) = ______ V

Graph 4-4: Monostable Operation for R = 33 k

Time base : ______ s/div, CH1 (Vpin 2) : ______ V/div, CH2 (Vout) : ______ V/div

* Note: Ask your instructor to verify your results before you proceed to Part C.


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CH1 ground

CH2 ground



VCC(meas) = _________V

Graph 4-5: Voltage-Controlled Oscillator at minimum frequency


Voltage-Controlled Oscillator at maximum frequency

* Note: Ask your instructor to verify your results.


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T = ________s

W = ________s

Vpin 6 (max) = ________V

Vpin 6 (min) = ________V

Vpin 5 = ________V

f = ________Hz

D = ________%

T = ________s

W = ________s

Vpin 6 (max) = ________V

Vpin 6 (min) = ________V

Vpin 5 = ________V

f = ________Hz

D = ________%

CH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 groundCH1 & CH2 ground


Discussion

A. Astable 555 Timer

1. Explain the difference between the calculated fcal and the measured f.

________________________________________________________________________

________________________________________________________________________

2. Compare the calculated Dcal to the measured D, and justify their difference.

________________________________________________________________________

________________________________________________________________________

3. Identify how the voltages Vout and Vpin 6 are related in the three graphs.

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

4. Compare between voltages VCC(meas) and Vout (max) and explain their difference.

________________________________________________________________________

5. Evaluate how WL, f and D changes when RA and/or RB are varied. Propose the expected

minimum and maximum duty cycle values.

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

B. Monostable 555 Timer

1. Identify how the voltages Vout and Vpin 3 are related in the three graphs.

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

2. Describe how W changes when R is varied.

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

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1. With the help of Figure 1 and Figure 3, compare and evaluate the relationships between

voltages Vpin 6 (max) and Vpin 5, as well as Vpin 6 (min) and Vpin 5. Include numerical calculations in

your answer.

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

2. Describe how W, f and D changes when the value of Vpin 5 is varied.

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

3. What is the voltage at pin 6 before the output of a monostable 555 timer changes from

ON state to OFF state? Why?

________________________________________________________________________

________________________________________________________________________

4. Why does the trigger pin 2 is pulled low only for a short period of time? How long can

pin 2 be maintained at low? What will happen if pin 2 is kept low indefinitely?

________________________________________________________________________

________________________________________________________________________

Conclusion___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

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EEE1026 Electronics II Experiment EB2STUDENT'S NAME:ID NO:

SUBJECT CODE AND TITLE: EEE1026 ELECTRONICS 2EXPERIMENT TITLE: EB2 – IC Multivibrator CircuitsEXPERIMENT DATE: TIME:

Criteria 1 (Need Improvement) 2 (Satisfactory) 3 (Good) 4 (Excellent)Rating Awarded by Assessor

Constructing the circuits and performing data collection using lab equipment1 Ability in constructing the

IC Multivibrator Circuits: Monostable, Astable and Voltage-Controlled Oscillator

Unable to demonstrateproper steps to construct the IC Multivibrator Circuits and not asking for help

Able to demonstrate basic steps required to construct the IC Multivibrator Circuits with some help

Able to demonstrate goodknowledge on the construction of the IC Multivibrator Circuits with minimum help

Able to demonstrate full knowledge on the construction of the IC Multivibrator Circuits without help

2 Ability in performing data collection using lab equipment such as DC power supply, digital multimeter, oscilloscope and function generator

Unable to record data, and no effort is shown

Able to provide adequatedata, and show some efforts in getting the data

Able to record most of the data correctly

Recorded all data neatly and correctly

3 Ability to determine and draw the time domain waveform for input and output voltages of the amplifier circuits

Not able to determine, and draw the time domain waveform for input and output voltages (no effort was also shown)

Able to at least determine and draw the time domain waveform for input and output voltages and show some efforts in the calculation

Able to determine and draw the time domain waveform for input and output voltagesand solve the calculations partiall

Completed all the drawing and calculations correctly

Conclusions4 The ability to present

results and summarise final outcomes which answers the objectives of the lab

Unable to present resultsclearly and no attempt was made to summarise final outcomes

Able to present results and summarise adequate final outcomes and reasonably relating them to the objectives

Able to present results and summarise mostly to the final outcomes and answered most of the objectives of the lab

Able to present results very clearly and excellent summary of final outcomes which answer the objectives of the lab

5 Ability to answer the questions in by Oral Assessment

Not able to answer the question, no attempt was made to answer

Able to answer questions with some basics answers and demonstrate some attempts to refer to the text books, notes, lab sheet

Able to answer most part of the questions, with some explanations and elaborations and demonstrate some attempts to refer to text books, notes or lab sheet

Answered all correctly with proper explanations and elaborations, without a need to refer to any references.

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Documents

Experiment EB2: IC Multivibrator Circuitsfoe.mmu.edu.my/lab/lab sheet/TRIM2/BETA/EEE1026-EB1,EB2... · Web viewExperiment EB2: IC Multivibrator Circuits Learning Outcomes LO4: Analyze