1 INTRODUCTION

The NOT gate has only one input and one output. It provides an output that is inverse of the input i.e. it changes a 1 at its input to a 0 at the output and vice-versa. The Boolean expression for NOT is expressed as a bar or a single prime (apostrophe) over the variable. If input A passes through two NOT gates, the result is 'double NOT A', which equals the input A. The NOT operation is called a unary operation since it operates upon only one variable. Conversely, the OR and AND operations are binary operations as two or more variables are involved.

1.1 NOT GATE

Description	Produces a HIGH output if the input is LOW and vice versa.
Symbol
Truth Table

1.2 APPLICATION: FUEL LEVEL INDICATOR

To indicate whether the fuel level in a tank has reached the minimum (reserve) level, a simple NOT gate along with a digital output level sensor can be used.

1.3 CONCEPT:

When the fuel level drops below the reserve/minimum level (1/4 th level of tank), the level- sensor gives output as logic HIGH. The NOT gate produces a LOW output, and the RED LED glows to indicate this fuel shortage status. To simulate the variation in the fuel level in the tank, a slider is provided.

Figure 1 Concept of Fuel Level Indicator