DIGLAB5 - Control of Analog to Digital Converters Aug 28

8/18/2019 DIGLAB5 - Control of Analog to Digital Converters Aug 28

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THE UNIVERSITY OF THE WEST INDIES

ST. AUGUSTINE, TRINIDAD & TOBAGO, WEST INDIES

FACULTY OF ENGINEERING

Department of Electrical & Computer Engineering

1

ECNG 2004

LABORATORY & PROJECT DESIGN IIhttp://myelearning.sta.uwi.edu/course/view.php?id=1678

Semester I, 2009/2010

1. GENERAL INFORMATION

Lab #: DIGLAB5

Name of the Lab: Control of Analog to Digital Converters

Lab Weighting: 5 % [TOTAL = 28 marks] Estimated total

study hours1:

5

Delivery mode: Lecture

Online Lab

Other

Venue for the Lab: Electronics Laboratory

Lab Dependencies2 The theoretical background to this lab is provided in ECNG 1014

Theoretical content link: http://myelearning.sta.uwi.edu/

Pre-Requisites – None

Recommendedprior knowledge

and skills3:

Course Staff Position/Role E-mail

Phone

Office Office

Hours

Marcus L George Instructor [email protected] ext3164 Electronics

Lab Office

Fridays

10am - 1pm


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THE UNIVERSITY OF THE WEST INDIES

ST. AUGUSTINE, TRINIDAD & TOBAGO, WEST INDIES

FACULTY OF ENGINEERING

Department of Electrical & Computer Engineering

2

2. LAB LEARNING OUTCOMES

Upon successful completion of the lab assignment, students will be able to: Cognitive

Level

1. Understand the concept of analog to digital conversion. C

2. Perform analog to digital conversion using the ADC08040 A/D Converter

IC.

C, Ap

3. Analyze the characteristics of the ADC08040 A/D Converter IC. An


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DIGLAB5: Control of Analog to Digital Converters

3. PRE-LAB

3.1. Required Reading Resources

Digital Design Principles and Practices, by John F. Wakerly

3.2. A/D Conversion Calculations

Digital computers and microcomputers are digital information processing systems, but

information quite often is in the analog form (eg. Speech, music and video signals). To process

this information with digital techniques it must first be converted from its analog to digital form.

The device that does this is known as an analog-to-digital-converter.

Analog to digital conversion is the process of converting analog signals to a digital

representation (please research analog to digital conversion to find out more information). In this

process a reference voltage, VREF must be specified. This is used by the analog to digital

converter to determine what binary value between 0 and 2n-1 that should be used to represent the

input analog signal to be converted to digital format. In this case ‘n’ represents the number of

bits used to represent the analog signal. For example if an analog signal must be represented in 8

bits then ‘n’ in this case will be 8. Therefore the range of possible values that the incoming

analog signal must be represented by is 0 – [28-1].

Due Date: • Must be submitted with the post-lab report. Make sure it is

properly attached to the post lab report

• The student’s name, ID number and group letter (E,F,G,H) must

be clearly stated on the cover of the pre-lab submission

Submission

Procedure:• Must be submitted with the post-lab report. Make sure it is

properly attached to the post lab report

Estimated time to

completion:

2 hours


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If we are required to calculate the 8-bit representation for an analog value, we are first required

to calculate the smallest change of the analog signal that corresponds to a bit-change in the

digital representation. For example, if the reference voltage is 5V and the input analog value

must be represented in 8-bits then the ‘smallest change’ in the voltage is given as follows:

Smallest change, ∆V = 5 / 2n = 0.0195 (to 4 decimal places)

Therefore we can use this approach to calculate the 8-bit binary representation of any analog

value. Hence the 8-bit binary representation of 2.4V is found as follows:

8-bit representation of 2.4 := [(2.4 / 5) × 2n] - 1= 122

= 122 corresponds to the 8-bit binary value 01111010

Therefore the 8-bit representation of 2.4 is 01111010

Exercise: Using the information obtained above and information obtained from other reading

material, fill out the tables below for VREF = 3V and VREF = 4.5V.

Table 1: Pre-lab table corresponding to a reference voltage of 3V

VREF / V VIN / V8-bit binary representation

Calculations Answer0.0 00000000

0.3

0.6

0.91.2

1.5

1.8

2.1

2.4

2.7

3 3.0


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Table 2: Pre-lab table corresponding to a reference voltage of 4.5V

VREF / V VIN / V8-bit binary representation

Calculations Answer0.0

0.40.8

1.2

1.6

2.0

2.4

2.8

3.2

3.6

4.0

4.5 4.5 11111111

V REF = reference voltage

V IN = input analog voltage

3.3. Reading Exercise

Download the datasheet for the ADC0804(you can also search for ADC0801) analog to digitalconverter. Thoroughly examine the datasheet, paying special attention to the following sections:

1. Connection Diagram

2. Absolute Maximum Ratings

3. AC Electrical Characteristics

4. Timing Diagrams

5. Functional Description


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4. IN-LAB

Allotted Completion

Time:

2 hours

Required lab

Equipment:

1 printed copy of the digital lab5 manual (students must bring to the lab)

1 - DC dual power supply

1 - Fluke Multimeter

1 - 1 small breadboard

1 - ADC08040 A/D Converter IC8 – LEDs(4 yellow LEDs & 4 red LEDs)

1 - 10k Ω Potentiometer

1 - 1.2k Ω resistor pack1 - 10k Ω resistor

2 – 1k Ω resistors

1 - 10μF capacitor1 – 150pF capacitor2 – 0.1μF capacitors

Connecting wires

1 - Pliers/Wire Cutter/Wire Nippers (students must bring to the lab)


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4.1.

In-Lab Procedure

ADC0804

10kΩ

10μF

150μF

0.1μF

0.1μF

A GND

D GND

START

1.2kΩ resistor pack

10kΩ

VREF

VREF

1

2

3

4

5

6

7

8

9

10

20

19

18

17

16

15

14

13

12

11MSB

LSB

VREF / 2

Location A

Wire X

1kΩ 1kΩVREF

Figure 1: Schematic for ADC control configuration ( based on figure 9 of ADC0804.pdf )


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4.1.1. Using the equipment provided for the lab, implement the system given in figure 1

above. Set up the circuit as shown figure 1 above. All analog and digital grounds must

be tied together. The four yellow LEDs will be connected to pin 11 - 14 of the AD0804,

while four red LEDs will be connected to pins 15 - 18.

4.1.2. Have your circuit checked by your instructor/teaching assistant before continuing.

4.1.3. Set VREF as 3V.

4.1.4. Connect wire X to ground for approximately 1 second and then disconnect and leave

unconnected.

4.1.5. By varying the resistance of the 10k Ω POT we vary the input voltage to the A/D

converter. Hence a new value is represented by the LEDs. You need to supply the inputvoltage to the A/D converter and observe the 8-bit value of the voltage displayed. Fill

out the table 3 below. ( Remember to use the Fluke Multimeter to obtain the actual

value of the voltage to the A/D converter). Record all observations made in the

discussion.

4.1.6. Show the functional system to your instructor/teaching assistant.

4.1.7. Set VREF as 4.5V and repeat section 4.1.2 to 4.1.6 above using table 4 below.


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DIGLAB5: Cont

For VREF = 3V

VIN / VStatus of LEDs( 1 or 0 ) 8-b

corresponLED7(MSB) LED6 LED5 LED4 LED3 LED2 LED1 LED0(LSB)

0.0

0.4

0.81.2

1.6

2.0

2.4

2.8

3.0Table 3: In-lab exercise results table(reference voltage = 3V)

For VREF = 4.5V

VIN / VStatus of LEDs(ON or OFF) 8-b

corresponLED7(MSB) LED6 LED5 LED4 LED3 LED2 LED1 LED0(LSB)

0.0

0.6

1.2

1.8

2.4

3.0

3.64.2

4.5Table 4: In-lab exercise results table(reference voltage = 4.5V)


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4.2.

Assignment:

4.2.1. Explain the process of analog to digital conversion as done by the ADC0804. [4 marks]

4.2.2. List all digital control inputs of the ADC0804 ADC. [1 mark]

4.2.3. How can we restart the A/D conversion process if currently in a cycle of A/D conversion?

[1 mark]

4.2.4. Calculate the 8-bit digital representation of the voltage 6.2V. In this case assume the

reference voltage(VREF) is equal to 8V. Show all calculations. [2 marks]


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4.2.5. After pre-lab calculations, a student discovered that a 4.3V is represented by the 8-bit

binary value ‘10011101’ when a VREF is equal to 7V. After testing the same scenario in the

lab, he obtained an 8-bit binary value of ‘10011111’.

a.

What is the most likely reason for the difference in the calculated and actual values

obtained? [1 mark]

b. Suggest a solution to the problem encountered. [1 mark]

4.2.6. Compare the results of the post lab exercise with pre-lab exercise.

a. Is there any difference between the 8-bit binary representation obtained in both the post

lab exercise and the pre-lab exercise? ______(Yes or No)

b. If any difference is found, then state the difference and explain possible reasons for this

difference.

4.2.7. Examine the schematic of figure 1 above. What is the significance of connecting pin 3 to

pin 5? [1 mark]

4.2.8. How can the accuracy of the 8-bit digital representation of analog inputs for this laboratory

exercise be improved using the same ADC pin assignments as used in this lab exercise?

Explain. [2 mark]


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4.2.9. As seen in the schematic of figure 1 above, the system consists of both analog and digital

grounds. Ideally we should not directly connect both analog and digital grounds together.

a. Why? [1 mark]

b. Explain with the aid of a well labeled diagram how we should set up the circuit of

figure 1, ensuring that all grounds(analog and digital) are correctly tied

together.(you don’t need to draw the entire schematic of figure 1) [2 marks]

4.2.10. Measure the voltage at location A stated on the schematic of figure 1 below, for V REF =

4.5V.

a. What is the value of this voltage? _______ [1 mark]

b. Sometimes the voltage of part(a) may be too small to register a logic ‘1’ on a pin of

the FPGA development board. Suggest and explain a solution to this problem. [2

marks


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c.

Using the blank space below, draw the modified circuit corresponding to the solution

suggested in part(c). Remember to attach this sheet of paper to the lab script. [3

mark]

Proceed to post-lab exercise.


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5. POST-LAB

A signed plagiarism declaration form must be submitted with your assignment.

Due Date: The deadline for submission of report for this laboratory exercise is as

follows:

All Groups: Monday 2nd

November 2009 at 12 noon

Feedback on Lab Feedback for this laboratory exercise will be given by Mr. Marcus

George on Friday 6th

November 2009 in the Electronics Laboratory

during office hours. Students’ lab marks will be made available.

Submission

Procedure:

Submit reports to designated graduate assistant in the Electronics

laboratory. Students must also fill out a report submission receipt and

have it signed or stamped by the graduate assistant.

Deliverables: Submit an informal report consisting of the responses to the post-lab

exercises in addition to a lab discussion and conclusion.

[1] Discussion of the lab should include: [3 mark]

a. Relate design to the results obtained.

b. If design was successful then explain why it works. If not

successful then explain why design did not work along with and

possible solutions.

c. Include and explain all observations made.

d. Design decisions made and justification for decisions made.

e. Problems faced and how were they dealt with.

[2] Conclusion of the lab should include: [1 mark]

State briefly, but clearly, what you have gained from this laboratory.

Outline aspects that you have noted within the experiment outside of the

questions asked. Make comments on the procedure of the lab - Is thereanything that you could have done differently? How did you split the

work between group members? Did you have a plan of action? What else

would you suggest that should be added to this lab session?

End of Lab #5: Control of Analog to Digital Converters

DIGLAB5 - Control of Analog to Digital Converters Aug 28

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