The objective of this experiment is to explore the basic logic gates in order to determine the behavior of the logic gates. The experiment is basically about the familiarization of the basic logic gates, their corresponding IC configuration and observing their behavior after inputting combinations of logic 1’s and 0’s.
Components and Materials Required
To carry out this experiment, we used the following:
14 pin Integrated Circuit
DC power supply
IC data sheet
In electronics, logic gates are the elementary building blocks of digital circuits. There different types of logic gates with each having its own distinct characteristics. Logic gates have input and output terminals. Some have a single input and also a single output e.g the NOT gate while others have two input and one output e.g AND gate. The input or output signals are discrete signals and they are characterized by either a logical one (high) or logical zero (low) depending on the voltage level. This experiment is only concerned with the following basic logic gates: NOT gate, AND gate OR gate, NOR gate and NAND gate.
The characteristics of the NOT gate is such that it ONLY produces an output when there is NO signal at its input. This characteristic is as shown in the truth table below. With this experiment, I intend to confirm its behavior.
This logic gate returns a logical zero (Low) when both inputs are low (logical zero) or either input are low. Its output will only be high (logical one) when both inputs are high (logical 1). Again, this can be shown in its truth table.
NAND gate (Not AND)
This gate has an output that is normally high (that is logic 1) and only goes low (logic level zero) when all of its inputs are high. Essentially, it is the opposite of AND gate. It is equivalent to the AND and NOT gate combined.
This gate produces an output signal if there is a signal on both or either of it inputs. That is, the output will only be high if one or both inputs is high. The output is ONLY low when both inputs are low. This characteristic is depicted in its truth table shown below.
This gate is also referred to as negated OR. This implies that it will have a high output ONLY when both inputs are low. Apart from this, any other combination of logic inputs will give a low at the output. It is essentially a combination of OR and NOT gate.
The procedure involves the use two IC’s, a NOT gate and one each of two input AND, OR, NOR and NAND integrated circuits. A typical 14 pin IC inverter and its pin designation is as shown below
+V power supply
Typical NOT gate IC
The notch on the IC is used as a guide to locating pin 1.
I was able to successfully wire up the breadboard and run the test. I tested all possible combination of inputs for each basic gate by applying the appropriate voltage that signifies logic 1’s (VIH) and 0’s(VIL) as specified by the IC data sheets.
As the different input combination is applied, I observed the output indicated by the LED. I also measured and recorded the corresponding output voltage levels. The circuit functioned properly with no glitch. The input voltages of 0 volt and +4.97 Volts were mapped to the Boolean values of 0 (LOW) and 1 (HIGH) as given by the data sheet.
The result is as tabulated below.
Discussion of Result and Conclusion
After careful observation of the results, I was able to verify that the truth table for each of the logic gates agreed with the theoretical truth table for each gate that was described in the background section of this report. I was excited by the outcome of this experiment. It was thrilling knowing that I actually created a functional digital circuit that operated as expected for each of the basic logic operators.