Breadboard Circuit Design Student · CleveLabs Laboratory Course System – Student Edition...

CleveLabs Laboratory Course System – Student Edition

Breadboard Circuit Design Laboratory

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CleveLabs Laboratory Course System Version 6.0






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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 used to 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 besides the 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 the modulation 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 on which 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 (electrically shorted 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 gap on the breadboard allows you to place integrated circuits (ICs) such as transistors, operational amplifiers or timing components onto the board.





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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, and operational 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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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 Figure 3 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 the integrator.

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 RR

xCR

F = 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 an operational 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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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 will determine 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

π= 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 Ground0





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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

π21

0 = with 24

3 =RR

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 signal generator circuits on the breadboard using the electrical components provided in your breadboard design 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 a 4.5V 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 the

9V 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 hole

between 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 battery connector to this terminal.

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

divider circuit.





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5. This row is the virtual ground in your circuit. You will need to connect other parts of the circuit 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 and provides 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 of an 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. Don’t connect

the 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 grounds should 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 amplifier pin layout





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6. The voltage at the output of the op-amp is higher than the maximum input specifications of 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 wave

output. 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=100 Ohms 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 0.1uF

Table 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

R1 2 1

Triangle Wave Output R3

2 1

0

R2 2 1

R6

100� R5

102K 0

0

U1

OPAMP +

- OUT

Square Wave Output

Virtual Ground

Virtual Ground

C1

1 2

U2

OPAMP +

- OUT 232K

R4

232K

19.5K

10.5K

0.1µF





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9. Using the alligator clip lead, connect the output of the square wave signal generator from

the 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 the jumper 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 Design

Laboratory” session under the “Engineering Basics” subheading.

14. Click on the green “Start” button. The BioRadio will be automatically programmed to the “LabBreadboardDesign” 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 the resolution of the FFT.

16. To change the amplitude of the square wave signal, disconnect the alligator clip from the

output. The amplitude of the output can be changed by adjusting the value of resistor value 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 output

of 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 R3 and 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 square wave 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 and R4 to a 47.5 KOhms resistor.

19. You will now observe the second output of the circuit you have created. Disconnect the

alligator 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 232KOhms R4 232KOhms R5 102KOhm R6 1KOhm C1 0.1uF

Table 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 the output 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 the

amplitude of the waveform by increasing R5 of the voltage divider circuit. Change R5 from 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

Virtual Ground

U1

OPAMP

+

- OUT

0

0

Virtual Ground

Triangle Wave Output

R1 2 1

R6

Virtual Ground

0 C1

1 2

R2 2 1

U2

OPAMP

+

- OUT

R3 2 1

R5

R4 2 1

19.5K�

10.5K�

232 K� 232 K�

0.1µF

102 K� 1 K�





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22. Disconnect the alligator lead from the output of the triangle wave output. Change the value 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 the triangle output.

23. Note the change of the waveform as the frequency increases. On the Spectral Analysis

tab, 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 the

breadboard 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 and R6 = 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 running

and the BioRadio 150 should be ON. Connect -Channel 1 of 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 the sine 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 1 to the output (Between R5 & R6) of the circuit. The amplitude of the sine wave now is around 55000uV 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 the output 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 of

the 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

C1 0.1uF

R1

Virtual Ground

R2

Virtual Ground 0

0 U1

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 the output 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.

Breadboard Circuit Design Student · CleveLabs Laboratory Course System – Student Edition...

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