EXCEL DIGI LAB
Hemant Yashwant Satpute
Electronic Science Department, Fergusson College, Pune 4
[Affiliated to University of Pune]
India (Maharashtra) hys0671@rediffmail.com Abstract
Being a teacher, my aim is to always encourage students and other colleague teachers to make optimum use of PC machine which one has purchased and full functionality of the softwares available with that machine. As an example, here I am illustrating use of EXCEL to learn Digital Electronics. One can verify Truth tables and study the working of various logic gates (AND, OR, NOT, EXOR, EXNOR, NAND, NOR), Various combinational logic circuits like Half Adder, Full Adder, Controlled Inverter, Multi bit adder, Multi bit subtractor,
Multi bit adder Subtractor, Multiplexers, Demultiplexers, Shift Registers, Flip flops, Counters,
Parity Generators and checkers using EXOR gates, Encoders, Decoders, Controlled
Inverter using EXOR gates and their uses and many more, by entering inputs directly and verifying outputs at various intermediate stages. One can also study use of universal gates to build various logic functions with the help of this tool. These outputs are derived by using various functions built in EXCEL. This was demonstrated to teachers and students. This idea helps teachers to make subject more illustrative and interesting. It has been proved to be an excellent tool for innovative class room teaching. This can be used as a learning material for open source learning and distance learning and which can be further extended to any subject.
Keywords - Virtual laboratory, open source learning material, effective tool for class room teaching, digital electronics, Excel digital electronics

1

INTRODUCTION

According to my experience of about 20 years in teaching field, I found that the use of computer in education is limited. One can afford to buy a latest PC but after that forget to make an optimum use of that machine. Also many times the powers of the softwares installed with the PC are also underutilized or many times not used at all. MICROSOFT’s EXCEL is one of such softwares which is learnt just for the sake of data entry, or plotting graphs or creating data base and that’s all. So an idea came to my mind to educate the people with the help of EXCEL to learn Digital Electronics. Many of the topics in
Digital Electronics are such that they have a specific relation ship between input and output or if not at least the outputs follow a particular sequence with respect to time. So with the help of EXCEL it is very easy to make a teaching aid. Hence here is an attempt to illustrate the use of EXCEL to learn Digital
Electronics. The project known as “EXCEL DIGI LAB”.

1.1

System Requirements

Though here I have used Microsoft Office 2007, but really speaking this project can run in any version of office. The functions / commands or techniques used in this project are as follows. (1) Logical functions available in EXCEL viz. AND, OR, NOT (2) IF function (3) Conditional Formatting of cells (4)
Data validation for cells (5) Insertion of Image (6) Hyper linking the cell contents to a particular worksheet sheet in a single workbook (7) Renaming a worksheet (8) Format painter tool to keep uniformity in the complete project through various worksheets (9) Nesting of IF functions along with all the logical functions (10) Protection of worksheets and protection of cells so that the choice is given for the user to select only a few cells and then depending upon the choice of the user the outputs are to be calculated. (11) Uses of smart graphics and their alignments, formatting etc.

1.2

Truth Tables of Basic & Derived Gates

Here one has to begin with INDEX. A separate worksheet named index has been created which lists about 40 topics in a single column. In next column, in front of each topic there is a hyperlink associated with the words “show me” which leads the user to the respective topic. I have started with the truth tables of various basic gates and derived gates such as NOT, OR, AND (Basic Gates) and
NAND, NOR, EXOR, EXNOR (Derived Gates). For each of the gate, a separate worksheet is used.
For truth tables, though all possible combinations are listed out, the user can change the inputs and verify the corresponding outputs for all the gates and can compare them. All the outputs are derived with the help of formulas.

1.3

Working of Each LOGIC GATE

Now, after learning the truth tables of various logic gates, the individual logic gate has to be studied for all possible combinations of it’s inputs. Hence, each gate is allotted a single worksheet. Here the symbol of the gate has been drawn with the help of “Circuit Maker 5” software and then it is converted into a .jpeg image with the help of “PAINT” accessory software available freely with windows. The user has to select the inputs by clicking on it, and then choose the value of the input as either “1” or
“0”. The corresponding output is then displayed next to the output of the gate. The output cell is applied conditional formatting. So that the background filling of the cell changes as per the value of the output. (Green for 1 and Red for 0). On every worksheet “BACK” hyperlink is also provided to return to
INDEX worksheet.

1.4

NAND & NOR as universal Gates

After learning the working of each individual gates, now it’s time to learn, why NAND and NOR gates are called as “Universal Gates”. So the use of these gates to derive all the other basic gates has to be studied. Again, separate worksheet is allotted to the use of NAND for building NOT, AND, OR gates and also the use of NOR for building NOT, AND, OR gates. Once again, user has to select inputs by clicking on the input cells and selecting the proper value of the input from the list. The corresponding final outputs and intermediate outputs can then be observed in the respective cells. All the output cells have been given conditional formatting. They change colours as per the value of the output. Red for zero and Green for one)

1.5

EXOR gate and it’s uses

Now, there is a time to study how EXOR gate can be constructed. The EXOR logic has been illustrated first. After that EXOR using NAND & NOR gates is illustrated. Next comes the uses of
EXOR gates as a Even and Odd parity Generator and checker, as a Controlled Inverter to find one’s compliment of a given binary number which then can be used for binary subtraction. All these have been illustrated on separate worksheets. On every worksheet “BACK” hyperlink is also provided to return to INDEX worksheet.

1.6

DeMorgan’s Laws

Next, two important theorems in Boolean algebra named as DeMorgan’s Laws, have been illustrated in separate worksheets. Through these worksheets, students have to learn about the concept of equivalence of two logic gates. Here for the first time, uses of smart graphics have been made to indicate the exact position of the intermediate stage output and also to state the equivalence between the two circuits.

1.7

Implementation of Boolean Logic Equations

Now, here is the time to implement all the gates to realize the function stated with the help of a
Boolean Equation. The student has to learn what a Boolean equation is and how to implement is using logic gates studied so far. Two illustrations have been taken into consideration here. Though, there is no limit for this exercise. One can extend this to each and every Boolean equation.

1.8

Arithmetic Circuits using Logic Gates

Now, there is a time to learn the uses of logic gates for performing binary arithmetic. Here I have illustrated the concepts of Half adder and Full adder. Also the construction of Full adder using NAND gates alone is also been illustrated. Construction of Full adder without using EXOR gate, but only using basic gates has also been considered in a separate worksheet. Note that, in all the worksheets, input cells have been given Yellow colour filling and the final output cells will change their background filling colour depending upon the value of the output. (Red for 0 and Green for 1)

1.9

Combinational Logic circuits using Basic Gates

Next, the use of logic gates to construct various logic circuits (whose outputs depend upon the present status of inputs only) has been now illustrated. Here, as an example 4 to 1 Multiplexer, 1 to 4
DeMultiplexer, Decimal to BCD Encoder has been illustrated. For encoder, to get correct output, only one input should be kept on “1” at a time as it is not a priority encoder. For checking the working of
Multiplexer and DeMultiplexer, first control inputs have to be selected and then the verification should be done by changing the input data line.

1.10 Sequential Logic Circuits using Universal Gates
After this, time comes for studying the sequential circuits. Here the response of the circuit is decided by not only the present status of the inputs but also the previous status of inputs as well as outputs. As an illustration, the workings of RS and JK Flip flops have been taken into consideration. RS Flip flop has been constructed using NAND and NOR gates separately. JK Flip flop has been constructed by using NAND gates alone. For checking the truth tables of these flip flops a particular sequence has to be followed, which is as follows. First the Flip flop has to be SET and then RESET. Next Last State or
Previous State is to be verified and finally the Forbidden or Race condition is to be tasted. All these are mentioned in the truth tables for these flip flops.

1.11 Results and Conclusion
Outputs of all the logic circuits have been tasted according to their truth tables. The Project is very easy to handle and too simple to experiment with. Technical experise is not essential to understand the working. The outputs displayed for various circuits are shown in figures 01 to 40. This Project was demonstrated to the group of teachers. Teachers found this highly useful for class room teaching as well as learning the basic concepts in digital electronics. This Project can be demonstrated with the power point presentation on the subject by clipping the outputs for various input combinations with the help of Microsoft Office One Note software. This can also be used by individual students to study the preliminary digital electronics concepts virtually.

1.12 Future Development
This project can further be modified with verbal instructions and with addition of some exercises based on the concepts learned by the students through this project. Also True /False type questions, Fill in the blank type questions, Multiple choice with single / multiple correct answer questions can be designed and student’s knowledge acquired can be judged. This idea can further be extended to any subject and any topic.

1.13 Screen Shots
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References
[1] Applied & Digital Electronics: P. K. Patil, M. M. Chitnis. Phadke Prakashan, 12th Edition (April
2008)
[2] An Introduction to Digital Electronics by Jamieson Rowe , B.P.B. Publications
[3] T.P.S. Electronics II by Kinnary Prakashan , 3rd Revised Edition
[4] Digital Electronics by H. R. Arvind , Vision Publications for FYBSc (Computer Science), 2nd
Revised Edition
[5] 2000 Solved problems in Digital Electronics by S. P. Bali. Tata McGraw-Hill Publishing Company
Limited
[6] Digital Electronics Principles and Devices by Malvino & Leach, Tata McGraw-Hill Publishing
Company Limited, 4th Edition