Lesson Notes By Weeks and Term v4 - SHS 2

Lesson Video

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Performance objectives

• Identify and describe the function of electronic components.
• Design a basic fire alarm circuit.
• Construct a rain alarm circuit and explain its operation.
• Analyze and troubleshoot basic electronic circuits.
• Apply calculations to determine values in a circuit.

Lesson summary

Time: [Enter Time] Overview and Learning Objectives

Lesson notes

This lesson focuses on practical application. We will use a Simple Fire Alarm Circuit as our main example to understand how components work together.

A. The Building Blocks: Basic Electronic Components

Before we build the house (the circuit), we must understand the bricks (the components).

| Component | Schematic Symbol | Function | Role in Our Fire Alarm Circuit Example | | :--- | :--- | :--- | :--- | | Resistor (R) | | To limit or control the flow of electric current. Measured in Ohms (Ω). | - 470kΩ, 100kΩ: These are used as biasing resistors. They control the small amount of current going into the base of the transistors, keeping them "off" until a fire is detected. - 1kΩ: This is a current-limiting resistor for the alarm's output (like an LED or buzzer) to protect it from burning out. | | Capacitor (C) | | To store electrical energy temporarily in an electric field. Can also be used to filter signals. Measured in Farads (F). | - 2.2µF: This capacitor helps to filter out false triggers or electrical "noise", making the circuit more stable. - 100µF: This is a larger capacitor used for power supply smoothing, ensuring the circuit gets a steady voltage from the battery. | | Diode (D) | | Allows electric current to flow in only one direction. It acts like a one-way street for electricity. | - 1N4007: This is often used for reverse polarity protection. If you connect the battery backwards by mistake, the diode blocks the current and protects the other components from damage. | | NPN Transistor (Q) | | An electronic switch or amplifier. A small current at its Base (B) controls a much larger current flowing from the Collector (C) to the Emitter (E). | - BC547/AC128: We will use two transistors. The first one (Q1) acts as a high-sensitivity switch. When it detects a small signal from the sensor, it turns on. When Q1 turns on, it then switches on the second transistor (Q2), which is powerful enough to drive the alarm (buzzer/siren). This is called a Darlington pair arrangement for high amplification. | | Power Source (Battery) | | Provides the electrical energy (Voltage and Current) to power the entire circuit. | - 9V Cell: This is the "engine" of our circuit, providing the 9 Volts needed for all the components to work. | | Sensor (Thermistor) | | A special type of resistor whose resistance changes significantly with temperature. An NTC (Negative Temperature Coefficient) thermistor's resistance *decreases* as temperature *increases*. | *Note: This component is essential for a fire alarm, though not explicitly in the exemplar list. We will add it to make our design functional.* This is the "detector". In normal conditions, its resistance is high. When a fire starts, it gets hot, its resistance drops, and this change triggers the circuit. | | Output (Buzzer) | | A device that converts electrical energy into sound energy. | This is what alerts us. When the circuit is triggered, it sends power to the buzzer, making it produce a loud noise. |

Evaluation guide

• Apply knowledge of electronic components in designing circuits
• Proposed materials to be used:
• Fire alarm circuit:
• Resistors (470k ω,100kω,and 1kω)