31) Breadboard Circuit Design

8/13/2019 31) Breadboard Circuit Design

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CleveLabs Laboratory Course System Student Edition

Breadboard Circuit Design Laboratory

2006 Cleveland Medical Devices Inc., Cleveland, OH.

Property of Cleveland Medical Devices. Copying and distribution prohibited.

CleveLabs Laboratory Course System Version 6.0

Breadboard Circuit Design

Laboratory


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1

Introduction

Signal generators are electrical instruments that generate repeating electronic signals. These

signals are useful for testing, troubleshooting, and repairing electronic devices. Many common

signals are triangle, saw-tooth, sine and square wave. An example of how these signals are usedto test a circuit is shown in Figure 1. A signal sine wave is input into an amplifier circuit, and

from here an engineer can observe the output of the circuit on the oscilloscope. The amplifier

circuit should provide a gain to the known sine wave signal. Any distortion on the output besidesthe signal being amplified can inform the engineer that something is wrong with the amplifier

circuit.

Signals generators are also extremely useful in communication devices such as a radio or

medical telemetry system. For example, a sine wave can be use as carrier signal in themodulation of a signal on the transmitter side of the radio system. The sine wave carrier is then

demodulated on the receiver side of the radio system.

Figure 1:Sine wave signal input to an amplifier and output to an oscilloscope.

For this laboratory session, a breadboard will be needed. A breadboard is a thin white board onwhich a prototype circuit with numerous connections for circuit elements is constructed. Figure

2 is an example of a typical breadboard layout. The top and bottom row are linked (electricallyshorted together) horizontally across, and typically used as the power supply. A battery + and

terminal can be connected to these holes and it would be linked horizontally across. The other

holes are electrical shorted together vertically in blocks of 5, with no link across. A center gapon the breadboard allows you to place integrated circuits (ICs) such as transistors, operational

amplifiers or timing components onto the board.


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2

Figure 2:A layout of a typical breadboard.

In previous laboratories, the Test Pak was used to generate a 10Hz square wave into the

BioRadio 150. In this laboratory, different components such as resistors, capacitors, andoperational amplifiers (op-amps) will be used to build a signal generator. The signals can then

be input into the BioRadio 150 and observed in the laboratory course software.

Equipment Required:

CleveLabs Kit

CleveLabs Course Software

Breadboard Circuit Design Kit

Multi-Meter


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3

Background

Square and Triangle Wave Oscillator

The signals that will be generated in this laboratory session are a square, a triangle and a sine

wave. These signals can be generated using two different circuits. The circuit shown in Figure3 will be used to generate a square and a triangle wave. A square wave will be generated first.

After successfully achieving the square wave, you will add an integrator to the circuit that will

integrate the square wave signal, and as a result, produce a triangle wave at the output of theintegrator.

Equation 1 specifies a square/triangle wave oscillator at a particular desired frequency. The

desired frequency depends on the components of the circuit, particularly the resistors and the

capacitors. Equation 1 determines the component values of your circuit to generate the desired

frequency of your waveform.

)(]4

1[

2

1

13 R

Rx

CRF = Equation 1

Wien Bridge Oscillator

A Wien Bridge Oscillator is shown in Figure 4. A Wien Bridge Oscillator is a typical circuit

used to generate a sine wave. This circuit consists of a few resistors, capacitors and anoperational amplifier.

Figure 3:Square and triangle wave oscillator

R121

Triangle Wave Output

R321

0

R221

0

U1

OPAMP

+

-

OUT

VirtualGround

Square Wave Output

VirtualGround

C11 2

U2

OPAMP

+

-

OUT


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4

Figure 4:Wien Bridge Oscillator

The circuit layout of the Wien Bridge Oscillator can be assembled as shown in Figure 5. This

layout can easily be implemented on a breadboard using electronic components. Equation 2 willdetermine the frequency of the sine wave that is generated. Equation 2 should be used to design

the sine wave to the desired frequency by selecting the appropriate component values.

2211

02

1

CRCRf

= Equation 2

Figure 5:Wien Bridge Oscillator

0

Virtual Ground

R3

C3

0.1uF

R4

Sine Wave Output

C2

0.1uF

R1

R2

U1

OPAMP

+

-

OUT

0

Virtual Ground Virtual Ground

0


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5

If the values of the resistors are RRR == 21 and the values of the capacitors are CCC == 21 ,

then the equation can be simplified to Equation 3. The value of 3R must be 2 times greater than

4R to provide sufficient loop gain for the circuit to oscillate.

RCf

2

10 = with 2

4

3=

R

R Equation 3

Experimental Methods

Experimental Setup

In this laboratory, various components such as resistors, op-amps, and capacitors, will be used to

build different circuits that will generate useful output signals. First you will build up the signalgenerator circuits on the breadboard using the electrical components provided in your breadboarddesign kit. Next you will connect the output of your breadboard circuit to the input of your

BioRadio so that your signal can be observed in the CleveLabs software interface.

Breadboard Power Supply

The power supply used in this laboratory is a 9V battery. The op-amp, however, requires a

dual-voltage supply. This means that one pin, the +V pin, on the op-amp must be connected to a4.5V input and another pin, the V pin, must be connected to a -4.5 input. To create the dual

power supply we will first setup a voltage divider circuit:

Note: The inputs between A and E of each row are shorted together. The inputs between F and I

of each row are also shorted together, but are not connected to A-E.

1. Figures 6 and 7 shows the connection on the breadboard required to split the voltage of the9V battery to act as a dual-voltage power supply.

2. Connect a 10K resistor between the red terminal (Va) and row 1 of the breadboard in a holebetween A and E. Also connect the red side of the 9V battery connector to this terminal.

3. Connect another 10K resistor between the black terminal (ground) and row 1 of the

breadboard in a hold between F and J. Also connect the black side of the 9V batteryconnector to this terminal.

4. Now connect a jumper wire between row 1 (A-E) and row 1 (F-I) to complete the voltagedivider circuit.


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5. This row is the virtual ground in your circuit. You will need to connect other parts of thecircuit to virtual ground as we build it. Therefore, to allow more room for connections,

connect a jumper between an open spot on row 1 to somewhere on row 3. Then jumper

sections A-E and F-I together on row 3. This makes row 3 also your virtual ground andprovides many places to connect to as you build your circuit.

6. Now connect a jumper wire from the red terminal (Va) to one of the slots on the red +column of the breadboard circuit. This will allow you to tap into a + 4.5 volt supply the

entire +V column down when measured against the virtual ground.

7. Now connect a jumper wire from the black terminal (ground) to one of the slots on the blue -column of the breadboard circuit. This will allow you to tap into a - 4.5 volt supply the entire-V column down when measured against the virtual ground.

Figure 6:Dual-voltage power supply using 9V battery

Figure 7:Dual-voltage power supply on a breadboard.


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Procedure and Data Collection

Square and Triangle Wave

The first circuits will be a square and triangle wave oscillator shown in Figure 9.

1. Place two op-amps on the center gap of the breadboard. Figure 8 shows the pin layout ofan LM741 Operational Amplifier. For convenience, the first should be placed such that

there are about 5 empty rows between it and the virtual ground row. The second op-amp

should be placed about 5 rows below that one.

2. Connect the V+ to pin 7 and V- to pin 4 of each op-amp to provide power. Dont connectthe 9V battery yet, as this will be done later after the circuit is complete. To do this, you

can connect a jumper from the + column which provides the +4.5V supply to each op-

amp pin 7 and a jumper from the column which provides the -4.5V supply to each op-amp pin 4.

3. Use the following components, R1 = 19.5K Ohms, R2 = 10.5K Ohms, R3 = 232K Ohms,R4=232K Ohms, and C1 = 0.1uF, to connect the circuit shown in Figure 9.

4. The op-amp non-inverting (+) is pin 3 and inverting (-) is pin 2. All virtual groundsshould be connected to the virtual ground created by the dual-voltage power supply(between R1 and R2 of the dual-voltage power supply).

5. The first op-amp will generate a square wave at its output, while the second op-amp will

generate a triangle wave.

Figure 8:LM741 operational


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6. The voltage at the output of the op-amp is higher than the maximum input specificationsof the BioRadio. Therefore, the voltage output needs to be decreased by setting up a

voltage divider.

7. A voltage divider needs to be set up for the square wave output and for a triangle waveoutput. The output voltage of the square wave is +/- 4V. This needs to be reduced to less

than +/- 100mV. The voltage divider should consist of a R5=102K Ohms and R6=100Ohms resistor. Figure 10 shows the connection to be made between the output of the

square wave generator and the voltage divider.

Figure 9:Output of square wave oscillator through voltage divider.

Component Value

R1 19.5KOhm

R2 10.5KOhm

R3 232KOhms

R4 232KOhms

R5 102KOhm

R6 100Ohm

C1 0.1uFTable 1. Electronic component values for original 10 Hz square wave shown in Fig 9.

8. Now connect the 9V battery snap connection to the battery terminals.

Virtual Ground

R121

Triangle Wave Outp

R321

0

R221

R6

100

R5

102K0

0

U1

OPAMP

+

-OUT

Square Wave Output

Virtual Ground

VirtualGround

C1

1 2

U2

OPAMP

+

-OUT232K

R4

232K

19.5K

10.5K

0.1F


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9. Using the alligator clip lead, connect the output of the square wave signal generator fromthe breadboard to the channel 1 input of the BioRadio as shown in Figure 10.

10.On the BioRadio, connect a jumper between the blue GND input and the -1 input.

11.Using the alligator clip lead, connect the virtual ground of the circuit to the input of thejumper on the blue BioRadio GND input.

Figure 10:Electrical connection between the BioRadio and breadboard circuit.

12.Turn the BioRadio On.

13.Start the CleveLabs software interface and enter the Breadboard Circuit DesignLaboratory session under the Engineering Basics subheading.

14.Click on the green Start button. The BioRadio will be automatically programmed to theLabBreadboardDesign configuration when you start the lab session.

15.A square wave should be scrolling across the graph at a 3500 uV peak (7000 uV Peak-Peak). Click on the Spectral Analysis tab to verify the circuit is operating at a frequency

of approximately 10Hz. Change the data collection interval to 300ms to improve theresolution of the FFT.

16.To change the amplitude of the square wave signal, disconnect the alligator clip from theoutput. The amplitude of the output can be changed by adjusting the value of resistorvalue R6 of the voltage divider to a larger value. Change R6 to 1K and re-connect the


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alligator lead to the output of the circuit. Notice that the amplitude of the square wave is

now 70000uV (Peak-Peak). Click the Spectral Analysis tab. Notice that the frequency of

the square wave is still at 10Hz.

17.To change the frequency of the square wave, disconnect the alligator lead from the outputof the square wave. Change R6 of the voltage divider back to 100 Ohms. To increase the

frequency of the square wave to 50Hz, decrease the value over R3 and R4. Replace R3and R4, each with a value of 232K Ohms, to a 93 KOhms resistor. After the changes have

been made, re-connect the alligator lead back to the output.

18.Notice the change in the waveform as the square wave scrolls across at 70000uV (Peak-Peak). Click on the Spectral Analysis tab to observe the new frequency of the squarewave waveform. Since the frequency is above 10, the range of the frequency needs to be

changed to 100Hz. Notice that the frequency of this waveform is around 50Hz. The

frequency can be increased again to 100Hz by repeating this step, and replacing R3 andR4 to a 47.5 KOhms resistor.

19.You will now observe the second output of the circuit you have created. Disconnect thealligator clip lead from the output of the square wave. Change the resistor R3 and R4

back to 232K Ohms each. Wire the output of the second Op Amp to a circuit divider

consisting of R5=102K Ohms and R6=1K Ohms resistor. Figure 11 shows this setup.


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Component Value

R1 19.5KOhm

R2 10.5KOhm

R3 232KOhmsR4 232KOhms

R5 102KOhm

R6 1KOhm

C1 0.1uFTable 2. Electronic component values for original 10 Hz square wave shown in Figure 11.

20.Now observe the output of the triangle wave circuit. Connect the alligator clip lead to theoutput of the triangle wave output. Observe the signal on the CleveLabs software

interface. Notice a triangle wave scrolling across the screen with 36000uV Peak-Peak.

Click on the Spectral Analysis tab. The frequency should be around 10 Hz.

21.Disconnect the alligator lead from the output of the triangle wave output. Increase theamplitude of the waveform by increasing R5 of the voltage divider circuit. Change R5from 1K to 2.17K and re-connect the alligator lead to the output of the triangle wave

circuit. The amplitude of the triangle waveform should immediately change to 80000uV

peak-peak. The frequency should still be 10 Hz in the Spectral Analysis Tab.

Figure 11:Setup of Triangle Wave Oscillator

VirtualGround

U1

OPAMP

+

-

OUT

0

0

Virtual Ground

Triangle Wave Output

R1

21

R6

VirtualGround

0C1

1 2

R221

U2

OPAMP

+

-

OUT

R321

R5

R421

19.5K

10.5K

232 K 232 K

0.1F

102 K 1 K


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22.Disconnect the alligator lead from the output of the triangle wave output. Change thevalue of resistor R5 of the voltage divider network back to 1KOhms. Now change the

triangle waveform to a frequency of 50Hz. To do this, simply change resistor R3 from

462K Ohms to 93K Ohms. Re-connect the alligator clip lead back to the output of thetriangle output.

23.Note the change of the waveform as the frequency increases. On the Spectral Analysistab, increase the frequency range from 0Hz to 100Hz. The frequency of this circuit has

increased to 50Hz. To increase the frequency to 100 Hz, repeat this step and change R3

to 47K Ohms. The amplitude can be changed by increasing resistor R5 to 2.17k Ohms.

Sine Wave

To set up the sine wave oscillator:

1. Disconnect the circuit previously set up, but leave the dual-voltage supply intact.Disconnect the snap connector from the 9V battery.

2. Figure 13 shows the Wien Bridge Oscillator circuit. Place the 741 op-amps onto thebreadboard and connect the battery terminal V+ to pin 7 and V- to pin 4. Figure 8 shows

the pin layout of the 741 op-amps.

3. The first sine wave should have a frequency of approximately 8 Hz and 28000uV Peak-Peak. Connect the circuit shown in Figure 12. The components should equal

C1=C2=0.1uF, R1=R2=163K Ohms, R3=26K Ohms, R4= 10 KOhms. The output of the

op-amp (pin 6) is connected to a voltage divider network, consisting of R5 = 102K andR6 = 550 Ohms to limit the voltage to the range of the BioRadio 150. All virtual grounds

need to be connected to the virtual ground created by the dual-voltage power supply.


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4. Connect the 9V battery to the battery snap connector. The software should be runningand the BioRadio 150 should be ON. Connect -Channel 1of the BioRadio 150 to the

virtual ground of your circuit board and connect +Channel 1 to the output of the sine

wave output, which is the point between Resistors R4 and R5. The software interface

should show a sine wave with amplitude around 28000 uV Peak-Peak. Note that the

frequency of this sine wave is around 8Hz.5. Disconnect the output of the circuit from the BioRadio 150. To increase the amplitude of

the sine wave, the value of resistor R6 can be increased. To increase the amplitude of thesine wave from 28000uV peak-peak to 55000uV peak-peak, simply change resistor R6

from 550 Ohms to 1KOhms. Once this is complete, re-connect +Channel 1to the output

(Between R5 & R6) of the circuit. The amplitude of the sine wave now is around55000uV peak-peak. Click on the Spectral Analysis tab, and note that the frequency

remains the same. Disconnect +Channel 1 from the circuit and change the value of

resistor R6 back to 550 Ohms.

6. To increase the frequency of the sine wave of the Wien Bridge Oscillator, decrease

resistor R2 and R2. The output of the BioRadio 150 should be disconnected from theoutput terminal of the circuit. Replace R1 and R2 with two 32K Ohms resistors to

increase the frequency to 40 Hz. Re-connect the alligator clip lead from +Channel 1 to

the output of the circuit (Between R5 & R6).

7. A much faster sine wave should be scrolling across the screen. Since the frequency ofthe sine wave increased, increase the range of the frequency in FFT Analysis from 0Hz to

Figure 12:Wien Bridge Oscillator Circuit

0

R5

R3

Virtual Ground

Virtual Ground

C10.1uF

R1

Virtual Ground

R2

Virtual Ground0

0U1

OPAMP

+

-

OUT

R6

0

C2

0.1uF

R4

Sine Wave Output

163 K

163 K

102 K 550

26 K

10 K


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100Hz. The frequency of the sine wave is now around 40Hz. The frequency of the sine

wave can be further increased by decreasing the value of R1 and R2. If R1 and R2 are

changed to 16KOhms, the frequency will increase to 80Hz. The amplitude can also be

increased by changing the value of R6 to 1 KOhm. Remember to first disconnect theoutput of the circuit from the BioRadio 150 before making any component changes to the

circuit.


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References

1. Thomas R.E. and Rosa A.J. The Analysis and Design of Linear Circuits. Prentice Hall,Englewood Cliffs, New Jersey, 1994.

Documents

31) Breadboard Circuit Design