Analog to Digital Converter Experiment in Remote Laboratory

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Analog to Digital Converter Experiment in Remote Laboratory

Aditya Prasanna Murthy

Dept. of Electronics and Telecommunication Engineering, Siddaganga Institute of Technology, Tumkur-03

Amrutha M

Dept. of Electronics and Telecommunication Engineering, Siddaganga Institute of Technology, Tumkur-03

Shilpa G S

Dept. of Electronics and Telecommunication Engineering, Siddaganga Institute of Technology, Tumkur-03

Suchitra V

Dept. of Electronics and Telecommunication Engineering, Siddaganga Institute of Technology, Tumkur-03

K C Narasimhamurthy

Dept. of Electronics and Telecommunication Engineering, Siddaganga Institute of Technology, Tumkur-03

AbstractThis paper describes the development and conduction of Analog to Digital Converter experiment based on IC 0808 that can be accessed remotely online. In this paper, performance analysis of ADC using remote laboratory is presented. Remote laboratory system has the option of selecting eight different analog inputs and obtain the equivalent digital output and measure the conversion error and conversion time. User has the control to change the clock frequency and instant of conversion as well as desired analog input. Remote laboratory system for oscillations is built using Aurdino ATMEGA-2560, National instruments (NI) Analog discovery kit and indigenously developed Printed Circuit Board. User has the freedom to conduct the experiment any number of times from anywhere with anyone.

Keywords Analog Discovery-2, ADC0808, Conversation time, Conversion error, Waveforms, Remote Lab, Disruptive Learning.

  1. INTRODUCTION

    Engineering education is all about experiential learning. Undergraduate Electronic engineering has many courses that are circuit/system design oriented. All these courses have an associated laboratory in the curriculum. Out of these few courses deal with Analog electronic circuits. The Concepts of these courses will be better understood by visualizing the concepts. There are many of visualizing these concepts: by using SPICE simulation integrated courses, project based learning. The Visualization can also be achieved by conducting theory classes in laboratories or creating a laboratory setup in the classroom itself. However, these above two options pose lots of financial constraints. One of the possible way is to use portable laboratory using Analog Discovery Module (AD Kit), a product of National Instruments Inc. AD Kit has necessary equipment to conduct Electronic circuits, like oscilloscope, Signal generator, Bode analyzer, spectrum analyzer, Digital IOs etc. However, this interrupts the class to a great extent, because students need to Rig up the circuit, get the output and take the readings to understand the concepts. One of the feasible option for experiential learning is to use Remote laboratory as a platform to bridge the gap between the theory and laboratory classes [1- 7]. In this paper an innovative approach of Remote laboratory for experiential learning of one of the important concept of Analog to Digital conversion is discussed.

    Economic pressures on universities and the emergence of new technologies have spurred the creation of new systems for developing engineering laboratories, in particular simulations and remote-access laboratory systems. These laboratories are similar to simulation techniques in which they require minimal space and time, because the experiments can be rapidly configured and run over the Internet from any place of the world. While accessing the virtual laboratory, the authorized user can select the desired circuit, vary the available parameters and observe the stimulated output. The simulated output is obtained as per the models files that are being used in the simulators and most of the cases the output differs from the real time outputs. This is because the models of the circuit components may not be representing many real time parameters.

    Data converters are important concepts to be learnt in engineering that includes Digital to Analog converters and Analog to Digital Converters. Both the converters are part of the Remote Laboratory system. In the conventional labs due to time constraints, complexity of the circuit and lack of experience, the important phase of learning: analysis of ADC will not be carried out. Important features of the IC0808, such as multiplexed analog input selection, measurement of conversion error and time are not usually measured. Only one or two analog signals at the same input channel will be measured. In this paper, details of the implementation of ADC in Remote lab with access to key parameters of the circuits, response of the circuit for those parametric variations are presented. In section 2 the description of development of ADC circuit for remote laboratory access is discussed. In further section the results are discussed and finally the paper is concluded.

  2. DEVELOPMENT OF ADC CIRCUIT FOR REMOTE LAB SYSTEM

    1. Bloak diagram of Remote Lab system

      The block diagram of remote laboratory system is shown in Fig. 1. Authorized user can login to remote laboratory and perform experiments on the circuits at anytime from anywhere. The remote laboratory system can be accessed using computer or Smartphone and it doesnt require any special software for accessing.

      Fig. 1. Block diagram of Remote Laboratory system

      Analog to digital converter is one of the important and challenging concept to understand. It is very essential students visualize them in during its introductory classes itself otherwise they think its difficult. As there are many types of ADCs in Remote lab system, one of the widely used Successive approximation type of ADC using IC 0808 is being implemented. Concepts like resolution, 1LSB, conversion time, errors in conversion can be determined quickly and efficiently.

      As the conduction of ADC experiment using IC 0808 is little complex in conventional labs, and students used to do mistakes in applying inputs and measuring many important parameters. In remote lab there are options to remote lab for Analog to Digital Converters has been developed to aid the authorized students by providing them immediate access to the ADC circuitry at anytime from anywhere. This paper describes how remote lab can help students to perform ADC experiment and obtain the results.

    2. Implementation of ADC circuit for Remote Lab system

    IC 0808 an ADC with 8:1 multiplexed input with giving 8 bit digital output. It also needs signals like: clock, start signal (SoC), address select input, address latch. IC gives End of conversion (EoC) signal indicating the 8 bit digital output D0- D7 are available as shown in Fig. 2

    Fig. 2. ADC IC0808 pin details

    The circuit implemented in the remote lab is shown in Fig. 3. Eight analog input are derived using potential divider network using nine resistors of equal value. Eight analog input voltage varies from Vcc/9 to 8Vcc/9 with an increment of Vcc/9.

    Fig. 3. Circuit diagram of ADC IC 0808 implemented in remote Lab system.

    The clock and Start of conversion & Address Latch Enable (ALE) signal are controlled by square waveform of Analog discovery channel 1 and channel 2 respectively. Digital output is observed using LEDs in the static IO option of AD kit and End of Conversion is observed on the scope, it is done to measure the conversion time of the ADC for different clock frequency and different analog input.

    Fig. 4. Prototype circuit of ADC implementation in Remote Laboratory

    Eight analog inputs of the ADC experiment is derived using series of resistors between +Vcc (5V) and round and are indicated as IN0 to IN7 as shown in Fig. 4. Eight digital outputs D0-D7 are also seen in Fig. 4 along with EoC and SoC signals using LEDs.

    The printed circuit board of the Remote laboratory system with ADC circuits developed indigenously is shown in Fig. 5. The circuit has many other analog electronic experiments like Amplitude modulator &demodulator, Frequency modulator & demodulator, II order Filters, RC & LC oscillators and others. The ADC IC 0808 used for experiment is also shown in Fig.

    5. All these circuits are controlled using an Arduino and analyzed using AD kit.

    Fig. 5. Printed Circuit Board of Remote Lab system and ADC experiment

    in particular.

    The GUI necessary to provide the online access to remote user is developed Users can apply any desired analog inputs by choosing any one from eight combinations from 000 to 111 as shown in Fig. 6. The GUI is implemented using the Python code. The implementation of selection of analog inputs is done using CMOS switches that are controlled by Arduino board.

    Fig. 6. GUI flow to conduct ADC experiment in Remote lab

    Through the Remote Lab welcome page, user can start the online access of experiments. User can choose the desired experiment from the dropdown menu. On selecting ADC experiment, user can select the desired analog input by choosing one of the eight combinations. Along with this user has the option of choosing the desired clock frequency and instant of starting the Data conversion through the wavegen of AD kit as shown in fig. 7. The user can apply the clock signal and Start & ALE signal using square wave with amplitude of

    2.5 V and offset 2.5 V that results in TTL compatible 0-5V signal. User must study the timing diagram of ADC 0808 before conducting experiment. As this Remote laboratory is not Plug and Play, user need to have the working knowledge of the ADC IC for verifying its performance. The advantage of the Remote Laboratory system is that, all the experiments are designed and connected in such a way that upon applying suitable input the user will surly get the output. Later do the parametric variations for the circuit analysis.

    Fig. 7. Wavegen option of the AD kit for clock and start signal variation

  3. RESUTS AND DISCUSSIONS

The Remote access of the ADC experiment provides an opportunity to the user to explore important performance analysis of ADC IC 0808. User can determine the conversion time for various clock frequencies and verify whether it take 64 clock cycles for data conversion as claimed in the datasheet or not. Error in conversion can also be verified by comparing the output with the theoretical values.

Fig.7. Digital Equivalent of the analog voltage observed on Static IO of Analog Discovery Kit.

The digital equivalent of the analog input is observed on the static IO of the Analog discovery kit. The same is shown in Fig. 7. Lower row of the static IO 0 to 7 shows the 8 bits digital equivalent of the input analog signal and three switches 8, 9 and 10 in the above row indicate the input select contol with 8 being the LSB of 3 bit select line.

The summary of the data conversion of eight different input analog signal from Vcc/9 to 8Vcc/9 to the corresponding eight bit binary output is shown in Table I. Table I shows the analog input being applied from the bank of resistors and the corresponding digital output and the conversion error compared to the ideal values. The table clearly shows that except for one analog input of 2.22 V, the error is within

+ ½LSB error as specified in the datasheet.

Address

Analog input and Digital output and error

Analog input

Digital output

Conversion error (LSB)

000

550mV

00011101

+ ½

001

1.11 V

00111001

– ½

010

1.66 V

01010101

0

011

2.22 V

01110010

+ 1½

100

2.77

10001110

0

101

3.33 V

10101010

– ½

110

3.88 V

11000111

+ ½

111

4.45 V

11100100

+½

Address

Analog input and Digital output and error

Analog input

Digital output

Conversion error (LSB)

000

550mV

00011101

+ ½

001

1.11 V

00111001

– ½

010

1.66 V

01010101

0

011

2.22 V

01110010

+ 1½

100

2.77

10001110

0

101

3.33 V

10101010

– ½

110

3.88 V

11000111

+ ½

111

4.45 V

11100100

+½

TABLE I. ADC INPUT, OUTPUT AND CONVERSION ERROR

One more performance parameter of the ADC is conversion time of the circuit. Remote lab provides an option to measure the same. The scope of the Analog Discovery kit is used to measure the same by displaying Start signal and EoC (End of Conversion) signal on to channel 1 and 2 of the scope respectively. Fig. 8 shows the same with cursors places from start of conversion to end of conversion.

Fig. 8. Start and EoC waveforms to measure the conversion time

Similarly the conversion time of the ADC IC 0808 for various clock frequencies is observed to verify the does the conversion time varies with the input analog magnitude or not. Its observed that the conversion time is independent of the input analog voltage magnitude because ADC IC 0808 uses successive approximation architecture. Table II shows that for various clock frequencies, obviously the conversion time changes, however its observed that the ADC IC takes 64 cycles to give the digital equivalent. These are all some key observation that can be done in quick time.

TABLE II. ADC CLOCK FREQUENCY AND CONVERTION TIME AND THE NUMBER OF CLOCK FOR DATA CONVERION

Clock

Frequency KHz

Conversion time

Number of cycles

10

6.48 ms

64

50

1.28 ms

64

100

64.2 µs

64

500

128.92 µs

64

CONCLUSION

Analog to Digital Converters are one of the important and complicated experiments at Engineering Undergraduate level. In this paper, implementation of ADC using IC 0808 in a remote environment is explained. The procedure to conduct the experiment and process of analysis of conversion error and measurement of conversion time is discussed. Its found that the conversion error for most of the input is within the limit of

+ ½LSB and the conversion time is 64 cycles of the clock.

ACKNOWLEDGMENT

Authors of this paper express their gratitude for all those who helped in developing the Remote Laboratory system. We also thank officials of Siddaganga Institute of Technology (SIT), Tumakuru, the Management, Director, CEO and Principal for their support in establishing Remote Laboratory system.

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