SAASTE Technology/Activities/AND and OR Gates

Electrical System Grade 8 AND & OR Logic Gates There are two types of electrical systems, viz. Digital and Analogue. Digital systems operate on logic circuits. The logic state or logic level of a system can either be HIGH or LOW. This high and low state is referred to as ON or 1 to represent High and OFF or 0 to represent Low. We use logic gates in electrical systems to decide in a logical way our desired output. Understanding a logic level The table is called a truth table. It shows the possible logic levels of the circuit by using a 1 to indicate ON and a 0 to indicate OFF. This circuit can also be represented as a Systems Diagram as follows: Activity 1: Practical, truth table and systems diagram Practical Gather the necessary components and connect up the circuit shown below: Truth Table Complete the truth table alongside the circuit This is an AND circuit &shy the lamp will only light up if S1 AND S2 are closed. Systems Diagram Draw a systems diagram to represent the AND circuit. Activity 2: Practical and truth table Practical Gather the necessary components and connect up the circuit shown below: Truth Table Complete the truth table below: S1 S2 L1 0 0 0 (off) 1 0 0 1 1 1 This is known as an OR circuit &shy for the lamp to light up either S1 OR S2 need be closed Glossary: Switch: a device which allows or prohibits electricity to flow. Conductor: a material which allows electricity to flow through it. All metals are conductors. Circuit diagram: a drawing which uses circuit symbols to represent components. Truth Table: represents the functioning of a digital circuit. This table uses a `1' to indicate a closed switch (or an `on' lamp, motor etc.), and `0' indicates an open switch (or an `off' lamp, motor etc.). Logic state or logic level: tell us if the system is high or low or on or off. Analogue system: has a range of values within its limits Digital system: have discreet values within its limits `AND' gate: produces 1 or high when all of its inputs are 1 or high `OR' gate: produces 1 or high when any of its inputs is 1 or high Author: Ricardo Miller Contributions by Osman Sadeck Editor: Osman Sadeck