Operational Amplifier - olsjdt | Our lady and St. John … · Web viewOne possible circuit is shown...

BTEC NATIONAL EXT DIPLOMA IN ENGINEERING

LEARNER NAME ASSESSOR NAME

N. Hodgson

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P4 (part) - build and test two different types of analogue circuit using operational amplifiers

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Internal Verifier ANTHONY SPICER

Signature A J Spicer Date

27/07/2012

Our Lady & St John Catholic College Engineering 1

UNIT 35 – Principles and Applications of Electronic Devices and Circuits (K/600/0300)

ASSIGNMENT THREE – INVESTIGATING THE OP AMP


Assessor's commentsQualification Edexcel Lev 3 National Diploma in

EngineeringAssessor name N. Hodgson

Unit number and titleUnit 35 – Principles and Applications of Electronic Devices and Circuits (K/600/0300)

Learner name

Assignment title ASSIGNMENT THREE – INVESTIGATING THE OP AMP

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P4 - Build and test two different types of analogue circuit using operational amplifiers

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Assignment Task 1 Task 1 - Temperature Controlled Sensor P4 - To Build and Test Operational Amplifier Based Analogue Circuits

Circuit Diagram –Temperature Controlled Sensor

Prototype / Breadboard Layout

Assembly1. Build the circuit shown above onto a prototyping board.

2. Use a +6v supply and a -6v supply to provide a dual power supply.

3. Set a voltmeter between the Non inverting input (pin 3) and 0v. Whilst adjusting the 100K Potentiometer record what is the maximum and minimum voltage?

Maximum voltage =___________ Minimum voltage =_____________

4. Adjust the 100K Potentiometer so that the voltage reads approximately zero.



5. Set a voltmeter between the Inverting input (pin 2) and 0v. What is the voltage reading at the current room temperature?

Voltage at Room temperature = __________________

6. Hold your fingers across the thermistor. What happens to the voltage now?

The voltage ____________ when the thermistor heats up

7. Allow the thermistor to cool back to room temperature. What happens to the voltage now?

The voltage _____________ when the thermistor cools.

8. Compare the voltages between question 4 and question 5. Which is higher?

____________________________________________________________

9. Which LED is lit? ________________

10. When the thermistor is at room temperature adjust the 100K potentiometer until the LED switches onto the other.

11. Measure the voltages at the inverting and the non-inverting input again. Which is higher now? ___________________________



The voltage at pin 6 will be either ________________ or ________________.

When the voltage is positive the _______ colour LED glows. When it is negative

the ___________ colour LED glows.

If the voltage at the Inverting input (Pin 2) is higher than the voltage at the Non-Inverting input (Pin 3) then the Output (pin 6) will be ___________________

If the voltage at the Non Inverting input (Pin 3) is higher than the voltage at the Inverting Input (Pin 2) then the Output (pin 6) will be ___________________

SummaryProduce a report that includes the following summary criteria. Attach the report to your completed assignment when you submit it.

A. What type of operational amplifier circuit have you built? Explain what an operational amplifier is and what it can do. Use reference research to show your understanding

B. Draw a block diagram of the circuit.

C. Draw the circuit diagram and identify what the main components used are.

D. Record and summarise your method of construction. (breadboard / prototype)

E. Use photographic evidence to demonstrate your completed investigation.

F. Identify why there may have been differences in the results between the simulated and the prototyped methods of building the op amp circuit.

This concludes the Task 1 investigation into the operational amplifier.



Assignment Task 2

Task 2 - MICROPHONE

To Build and Test Operational Amplifier Based Analogue Circuits

This assignment will satisfy part of the criteria for P4

P4 Build and test two different types of analogue circuit using operational amplifiers

Activity Tasks

1. You are going to build and test a Microphone circuit that will amplify a voice and plot the resultant output waveform on an oscilloscope

2. You will build and test a 741 analogue Operational Amplifier circuit that uses the microphone circuit as an input.

This assignment uses resources that can be found on

http://www.doctronics.co.uk/scope.htm - circuit 3 Accessed March 2013


http://www.doctronics.co.uk/scope.htm#circuit%203


Microphone Input

This part of the Practical is an investigation of microphones, audio signals and amplifiers, intended to develop your prototype board skills and giving you experience of using the oscilloscope to monitor signals in a simple circuit.

The diagram shows an easily available type of microphone, called a cermet microphone:

The microphone has separate + and 0 V connections. Can you see that the 0 V connection is connected to the metal case? Check these connections on the real component.

To get the microphone to work, you need to provide a voltage across it using a voltage divider circuit:

From the voltage divider formula, the voltage expected across the microphone is:

Build the Voltage Divider Circuit on a breadboard. Use a Voltmeter to :-

Measure the voltage between the resistors.

Voltage = ________________

How closely does the measured value agree with the calculated one?

Voltage Difference = _______



Possible Reasons for a Difference in Results.

Small differences in expected results can arise if you have not provided the power supply voltage to exactly 9 V and also because the resistors may not have precisely their marked values. Remember, resistors are manufactured to a tolerance, usually ±5%, so that their values are not exact.

Addition of the Microphone

Now add the microphone to the circuit, taking care to get its + and 0 V connections the right way round:

When the microphone is added, this results in a small decrease in the voltage divider voltage, because the microphone is now in parallel with the 1 resistor. In other words, Rbottom from the Voltage Divider formula is reduced. Another way of explaining this is to say that some of the current flows through the microphone, leaving a little less flowing through the 1



Adding the 4.7 uF Capacitor

Check the polarity of a 4.7 µF or 10 µF capacitor (longer leg positive, stripe negative) and connect this as indicated below

Now in this circuit, the capacitor blocks DC voltages, but allows AC voltages, including audio signal, to pass

Setting up the Oscilloscope to Trace the Microphone Signal

The arrangement outlined below is a very convenient way of setting up an oscilloscope to make measurements from the prototype circuit:

Once the crocodile clip corresponding to the black lead has been connected to 0 V, it can be ignored. This leaves the test probe which can be connected to any point in the circuit to monitor the signals present.

Connect the test probe to the prototype circuit as indicated. Increase the sensitivity of the VOLTS/DIV control by rotating it clockwise until you can see changes on the oscilloscope screen when you talk into the microphone. Adjust TIME/DIV until the shape of the signals is clear.


Oscilloscope


Results of Oscilloscope Test for the Microphone

In the space below, make a drawing to represent the V/t graph of an audio signal:

How large is your signal in mV, peak-to-peak amplitude?

What sort of signal is produced if you clap your hands within range of the microphone?



This concludes the measurement of the microphone circuit using an oscilloscope



Operational Amplifier

When you talk into the microphone, the signals you get are small. To make them bigger, you need an amplifier. One possible circuit is shown below. This uses a 741, one of a large family of integrated circuits called operational amplifiers, or op-amps

The internal circuit of a 741 is quite complicated but it is easy to use the device simply as an amplifying subsystem.

It is cheap and easily available. As you can see, the 741 is manufactured in a small plastic package, with 8 connecting pins. These are in a dual in line, or DIL arrangement.

With the index mark at the top, pin 1 is on the left and pins are numbered down the left hand side and back up on the right.

Often, there is an additional circular mark next to pin 1. This numbering convention is followed on other integrated circuits, whether there are 8, 14, 16, or more pins.


Figure 1:- 741 Op Amp schematic and 8 pin Integrated package


Build the Operational Amplifier Circuit

Place the 741 across the central gap in the prototype board. Check that pin 1 is correctly located. Now complete the circuit, as follows:

Dual Power Supply

The +9 V, 0 V, -9 V dual power supply required can be made using two PP3 batteries, connected to the prototype board as shown:-



Testing the Operational Amplifier

Check back with your prototype board and make sure that you have linked the SENSOR subsystem to the AMPLIFIER with a wire link.

Monitor the final output of the system using the oscilloscope. The signals should have increased in magnitude.

Gain Calculation

The voltage gain of the amplifier is given by:

The way in which this particular op-amp circuit works allows you to choose the voltage gain according to:

The minus sign appears because this is an inverting amplifier circuit, that is, the output waveform has the same shape as the input waveform, but is turned upside down, or inverted, compared with the input waveform. What matters here is that the amplitude of the waveform is increased.



The voltage gain of the circuit is calculated from:

Vout is inverted and the amplitude of the signal is increased by 47 times.

Vout after the amplifier should be 47 times larger than the signal from the microphone subsystem

Do your observations using the oscilloscope confirm these changes?

Produce a summary of your observations. Include a measurement of the average peak to peak amplitude of the amplified signal if you clap your hands within range of the microphone?



Use this page to attach photographic evidence of your build and testing of the circuits on breadboard. Include photographs of

measuring the circuit output using the oscilloscope

This concludes the Task 2 investigation into the operational amplifier.



Appendix

The Operational Amplifier comparator circuit converts a ‘changing’ analogue input signal into a digital output signal. The analogue input signal could be ‘heat’, ‘light’, or ‘moisture’, etc.

A small change in the changing input signal provides a large change in output. The output signal can be +VE Voltage or –VE Voltage. This could be used to switch on a forward biased LED or a reverse biased LED.

The Operational Amplifier operates using a ‘Dual Power Supply’. This allows a voltage range to be used in a positive or negative direction and measurements to be set in between the limits of the values. (Vs+ and Vs-)

The Output voltage (pin 6) of an Operational Amplifier (Op-Amp) is affected by the voltages of its two inputs.

The inverting input V- (pin 2)

The Non-inverting input V+ (pin 3)

When the voltage at pin 2 is bigger than the voltage at pin 3 then the output voltage (pin 6) should be low.

When the voltage at pin 3 is bigger than the voltage at pin 2 then the output voltage (pin 6) should be high.

The Operational Amplifier circuit makes good use of the Potentiometer.

Variable resistors used as potentiometers have all three terminals connected.


INPUT PROCESS OUTPUT

TEMP. CHANGING VOLTAGE (at Pin 2)

COMPAREOUTPUT High or low voltageREFERENCE

VOLTAGE (at Pin 3)


This arrangement is normally used to vary voltage, for example to set the switching point of a circuit with a sensor, or control the volume (loudness) in an amplifier circuit. If the terminals at the ends of the track are connected across the power supply then the wiper terminal will provide a voltage which can be varied from zero up to the maximum of the supply.

Datasheet

http://www.national.com/ds/LM/LM741.pdf

Revision Link

http://www.kpsec.freeuk.com/components/vres.htm#presets

http://www.technologystudent.com/elec1/opamp1.htm

http://www.techitoutuk.com/knowledge/electronics/buildingblocks/opamp/index.html


http://www.techitoutuk.com/knowledge/electronics/buildingblocks/opamp/index.html

http://www.technologystudent.com/elec1/opamp1.htm

http://www.kpsec.freeuk.com/components/vres.htm#presets

http://www.national.com/ds/LM/LM741.pdf

Operational Amplifier - olsjdt | Our lady and St. John … · Web viewOne possible circuit is shown...

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