Lab Report on Logic Circuits (Lab Report Sample)

Student’s Name
Teacher’s Name
Course Title
Date
Lab Report
Abstract
This laboratory report was done mainly for the study of the logic gates. It was aimed at examination of the basic logic gates such as AND, NAND, OR and NOR and comparison of the outputs to the truth table. The experiment was also aimed at study of the behavior of the gates such as 74xx series TTL gates by using voltage range of 0 and +5. This lab was finally based on laying out the simple test circuit on the on the prototype board and identification and testing of the output level of the gates using LEDs.
Introduction
Logic gates always have one output and two or more inputs. They bond with the digital basic levels on the input which make them provide digital basic level output. This depends entirely on the applied input to the gate and the logic gate type used. In this experiment, AND, OR and NOT gates are used to determine the combination of binary inputs and there corresponding output. Other complicated logic gates such as NOR, X-NOR, and NAND gates are constructed from the basic logic gates. Input and output combinations are shown in a truth table. Combination of more than one gate is possible hence this can give a desirable output.
Some of the equipment that were used during the experiment are;
* DC power supply with variable voltage
* 2 DVM’s
* Chip extraction tool
* Prototype board (with 5 V supply) jumper kit
* LED + 470 Ω current- limiting resistor and digital chips (AND-7408, OR-7432, NOT-404, NAND-7400, NOR-7402).
Procedure
The output voltage of an AND gate was measured when one of the inputs was zero and the other was a zero or a one. One of the AND inputs was grounded or set to "0" and variable voltage applied in the range of 0V – 5V to the next input. LED and a 470 Ω resistor were used on the AND output to test if "0" or "1" states exist and this followed with determination of minimum and maximum input voltage that was required to turn the output from a "0" a "1”. The purpose of the resistor is to limit the amount of current through the LED to avoid burning the light emitting diode (LED). The lights when the output is 1 (logic 1) and does not light when output is 0 (logic 0)
AND gate
0K (output)
1
After the above procedures, determination of which pins on one the SPDT switch was connected for each of the switch states that were connected then one switch on each input was used to switch between +5V. Identification of the truth tables of the standard gates followed whereby the five chips in the basic TTL series were obtained and the measurement of truth tables in the IC chips there were present. Construction of XOR using and XNOR gates using AND, OR and NOT gates only was done and determination of the truth tables at the output and at many intermediate points in the constructed circuit. Finally XOR gate was constructed using the NAND gates only. The following are mathematical formulas for determining output from a given set of inputs in logic gates.
Logic Gate

Formula for output (X), (where A, B, or C are binary inputs-0 or 1)

AND

X = A. B. C (multiplication) read as A AND B AND C

OR

X = A + B + C (addition) read as A OR B OR C

NOT

X = A-1(Inversion)

NAND

X equals NOT (A AND B AND C)

XOR

X equals NOT (A OR B)

XNOR

It complements XOR

Truth table for OR gate
A

B

X

0

0

0

0

1

1

1

0

1

1

1

1

Truth table for AND gate
A

B

X

0

0

0

0

1

0

1

0

0

1

1

1

Truth table for NOT gateTruth table for NAND gate
A

A-1

X

0

1

1

1

0

0

A

B

C

X

0

0

0

1

0

0

1

1

0

1

0

1

0

1

1

1

1

0

0

1

1

0

1

1

1

1

0

1

1

1

1

0

(Source: BooRan)
Results of the experiment
After the experiments the results were collected and conclusion drawn. All the logic gates have one output and two or more inputs. AND is the same as the product in mathematics and it gives only a result of logic 1 output provided all the gate inputs are at logic 1 and logic 0 outputs for all other input combinations. NAND is a complement of the AND function whereby the inversion occurs on the output. It gives only logic 0 at the output even if both inputs are logic 1 and for the entire combined diagram it gives logic 1 output. OR function is also just like addition and the analysis of its output can be calculated using the addition law. If all the outputs are logic 0 then definitely the inputs must be logic 0 given that the input is also logic 1 .Combination of NAND gates inputs or that of NOR gate gave out a NOT function which is also called an inverter. It was found That XOR gate is the inverse of XNOR gate. Its output is 1 provided both of its output is 0 of 1. XNOR provides no output if the inputs are at the opposite logic level. The XOR gates are present always as the basic components and it functions the same way equivalent to AND, OR, and NOT gates. The XNOR gate also performs the same function equal to AND, OR and NOT gates. It’s applied mostly in digital system application. Both XOR and XNOR are used in detection of both similar and dissimilar inputs. TTL are being designed using transistors which are combined differently to produce a switching circuit. In this kind of combination the transistor acts as a switch because if the bias voltage is applied the transistor switches on and it switches off if the bias voltage is removed. For a better functionality the transistor should operate under low voltages not under high voltages this is to reduce the power consumption. This is
Below is the truth table.
Truth table
A

B

K

0

0

1

0

1

0

1

0

0

1

1

0

1 Boolean equation gives K= A+B
K is the output.
A, B represents the input.
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