Lesson Notes By Weeks and Term v4 - SHS 3
ELECTRONIC COMPONENTS AND CIRCUITS
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ELECTRONIC COMPONENTS AND CIRCUITS
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Subject: Applied Technology
Class: SHS 3
Term: 2nd Term
Week: 17
Grade code: 2.5.2.LI.7
Strand code: 4
Sub-strand code: 2
Content standard code: 2.5.2.CS.1
Indicator code: 2.5.2.LI.7
Theme: ELECTRICAL AND ELECTRONIC TECHNOLOGY
Subtheme: ELECTRONIC COMPONENTS AND CIRCUITS
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This lesson introduces learners to the fundamental building blocks of all digital devices: logic gates. We will explore how these simple components make "decisions" based on logical rules. Everything from the smartphone in your pocket used for Mobile Money (MoMo) transactions to the traffic lights in Accra and Kumasi, and even complex computers, operates on the principles of logic gates. Understanding them is the first step to understanding how the digital world works.
A. What are Logic Gates? A logic gate is a basic building block of a digital circuit. Think of it as a tiny electronic decision-maker. It takes one or more binary inputs and produces a single binary output based on a specific logical rule. Binary System: Digital electronics work with two states: HIGH (or ON, True), represented by the number 1. LOW (or OFF, False), represented by the number 0. Analogy: Imagine a security guard at a gate. The guard has rules. For example, "Let the person in ONLY IF they have an ID card AND they are on the guest list." This is a logical decision, just like an AND gate makes. B. Truth Tables A truth table is a chart that shows every possible input combination for a logic gate and the corresponding output for each combination. It is the clearest way to describe how a logic gate behaves. C. Boolean Expressions A Boolean expression is an algebraic way to represent the function of a logic gate. It uses variables (like A, B, C) for inputs and symbols for logical operations. It's a shorthand for the gate's rule. D. The Basic Logic Gates
We will explore seven fundamental logic gates. The AND Gate Function: The output is HIGH (1) only if ALL its inputs are HIGH (1). Analogy: A series circuit with two switches. A light bulb will only turn on if Switch A AND Switch B are both closed (ON). Symbol: Boolean Expression: `Q = A . B` (Read as "Q equals A and B") Truth Table (2-input): | Input A | Input B | Output Q | | :---------: | :---------: | :----------: | | 0 | 0 | 0 | | 0 | 1 | 0 | | 1 | 0 | 0 | | 1 | 1 | 1 | The OR Gate Function: The output is HIGH (1) if AT LEAST ONE of its inputs is HIGH (1). Analogy: A parallel circuit with two switches. A light bulb will turn on if either Switch A OR Switch B (or both) are closed (ON). Symbol: Boolean Expression: `Q = A + B` (Read as "Q equals A or B") Truth Table (2-input): | Input A | Input B | Output Q | | :---------: | :---------: | :----------: | | 0 | 0 | 0 | | 0 | 1 | 1 | | 1 | 0 | 1 | | 1 | 1 | 1 | The NOT Gate (Inverter) Function: The output is always the OPPOSITE of the single input. It inverts the input. Analogy: A simple switch that controls a "Power On" light. When the switch is OFF (0), the light is ON (1). When the switch is ON (1), the light is OFF (0). Symbol: Boolean Expression: `Q = Ā` (Read as "Q equals NOT A" or "A bar") Truth Table (1-input): | Input A | Output Q | | :---------: | :----------: | | 0 | 1 | | 1 | 0 | The NAND Gate (NOT-AND) Function: It is an AND gate followed by a NOT gate. The output is LOW (0) only when ALL inputs are HIGH (1). Symbol: An AND gate symbol with a small circle (bubble) at the output. Boolean Expression: `Q = A . B` with a bar over the top ( `Q = Ā.B` ) Truth Table (2-input): | Input A | Input B | Output Q | | :---------: | :---------: | :----------: | | 0 | 0 | 1 | | 0 | 1 | 1 | | 1 | 0 | 1 | | 1 | 1 | 0 | The NOR Gate (NOT-OR) Function: It is an OR gate followed by a NOT gate. The output is HIGH (1) only when ALL inputs are LOW (0). Symbol: An OR gate symbol with a bubble at the output. Boolean Expression: `Q = A + B` with a bar over the top ( `Q = Ā+B` ) Truth Table (2-input): | Input A | Input B | Output Q | | :---------: | :---------: | :----------: | | 0 | 0 | 1 | | 0 | 1 | 0 | | 1 | 0 | 0 | | 1 | 1 | 0 | The XOR Gate (Exclusive-OR) Function: The output is HIGH (1) only if the inputs are DIFFERENT. Analogy: A staircase light switch. You can turn the light on or off from either the top or bottom of the stairs. The light is ON when the two switches are in different positions. Symbol: Boolean Expression: `Q = A ⊕ B` Truth Table (2-input): | Input A | Input B | Output Q | | :---------: | :---------: | :----------: | | 0 | 0 | 0 | | 0 | 1 | 1 | | 1 | 0 | 1 | | 1 | 1 | 0 | The XNOR Gate (Exclusive-NOR) Function: It is an XOR gate followed by a NOT gate. The output is HIGH (1) only if the inputs are the SAME. It's sometimes called the "equality gate". Symbol: An XOR gate symbol with a bubble at the output. Boolean Expression: `Q = A ⊕ B` with a bar over the top (`Q = Ā⊕B`) Truth Table (2-input): | Input A | Input B | Output Q | | :---------: | :---------: | :----------: | | 0 | 0 | 1 | | 0 | 1 | 0 | | 1 | 0 | 0 | | 1 | 1 | 1 |
Guided Practice (With Solutions)
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