Lesson Notes By Weeks and Term v4 - SHS 2
Sensors & Actuators
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Sensors & Actuators
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Subject: Robotics
Class: SHS 2
Term: 1st Term
Week: 18
Grade code: 2.1.3.LI.2
Strand code: 1
Sub-strand code: 3
Content standard code: 2.1.3.CS.1
Indicator code: 2.1.3.LI.2
Theme: Principles of Robotic Systems
Subtheme: Sensors & Actuators
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Welcome, future engineers and innovators! Look around you. Your smartphone knows when to rotate its screen. Streetlights in Accra automatically turn on when it gets dark. A security light at home switches on when someone passes by. How do these devices "see" or "feel" the world? They use sensors. Sensors are the eyes, ears, and skin of any smart device or robot. Understanding how they work is the first step to building our own amazing creations. In Ghana, from improving our farms with smart irrigation to making our homes safer, sensors are becoming more and more important. Today, we will learn how to categorise these important components, which is a key skill for any robotics enthusiast.
This lesson focuses on two key ways to classify sensors. Think of it like classifying students in a school: you can classify them by their *grade level* (SHS1, SHS2) and also by their *house* (Aggrey, Bota). A sensor also has two "classifications" we can assign to it at the same time. Classification Axis 1: Active vs. Passive (How it Senses)
This classification is based on whether the sensor needs to produce its own energy to detect something.
A. Passive Sensors: A passive sensor is like your ears. It simply detects energy that is already present in the environment. It "listens" or "waits" for a signal like light, heat, or sound to come to it. It does not send out any energy of its own to perform its measurement. Analogy: A passive sensor is like a market woman sitting at her stall, waiting for customers to come to her. She doesn't go out to find them. Key Idea: It measures ambient (existing) conditions. Example 1: Light Dependent Resistor (LDR) An LDR detects the amount of light falling on it. It doesn't produce its own light. It just reacts to the sunlight or room light that is already there. The more light, the lower its resistance. This is why it's used in automatic streetlights that turn on only when it gets dark (low ambient light). Example 2: Passive Infrared (PIR) Motion Sensor This sensor detects the infrared radiation (body heat) that is naturally emitted by warm bodies like humans and animals. It doesn't send out any beams. It passively waits to detect a change in the heat signature in front of it.
B. Active Sensors: An active sensor is like a bat using echolocation. It emits its own energy (like a sound wave or a light beam) and then measures how that energy is reflected or changed by the environment. Analogy: An active sensor is like a "trotro mate" calling out for passengers. He is actively sending out a signal (his voice) to get a response (passengers). Key Idea: It sends a signal (probes the environment) and detects the response. Example: Ultrasonic Distance Sensor (HC-SR04) This sensor has two parts: a "speaker" (transmitter) and a "microphone" (receiver). It sends out a high-frequency sound pulse (which humans cannot hear). This pulse travels, hits an object, and bounces back. The sensor measures the time it takes for the echo to return. Because it *generates the sound itself*, it is an active sensor.