Lesson Notes By Weeks and Term v4 - SHS 1
Sensors & Actuators
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Sensors & Actuators
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Subject: Robotics
Class: SHS 1
Term: 1st Term
Week: 14
Grade code: 1.1.3.LI.2
Strand code: 1
Sub-strand code: 3
Content standard code: 1.1.3.CS.1
Indicator code: 1.1.3.LI.2
Theme: Principles of Robotic Systems
Subtheme: Sensors & Actuators
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Welcome, learners! Think about how you know if it's hot or cold, bright or dark, or if something is close to you. You use your senses: your skin feels temperature, your eyes see light, and you can hear or see how far things are. Robots also need to understand their environment to do their jobs. They use special electronic components called sensors to act as their "senses." Today, we will explore what sensors are, how they work by looking at the science behind them, and how they are used right here in Ghana to solve problems. Understanding sensors is the first step to building intelligent machines that can help our communities.
A. The Basic Robotic System: Sense, Think, Act
Every useful robot follows a simple cycle: Sense: The robot gathers information about its surroundings using sensors. (e.g., "Is there an obstacle in front of me?") Think: A computer or a small chip called a microcontroller (like the "brain") processes the information from the sensors and decides what to do based on its programming. (e.g., "If there is an obstacle, I must stop.") Act: The robot carries out the decision using actuators, which are the parts that create movement or action (like motors, lights, or speakers). (e.g., "Stop the wheels from turning.") Sensor: A device that detects or measures a physical property (like light, heat, or distance) and converts it into an electrical signal that a computer can understand. Sensors are the inputs of a robot. Actuator: A device that converts an electrical signal from the computer into a physical action or movement. Actuators are the outputs of a robot. Examples include electric motors, LEDs (lights), buzzers (sound), and hydraulic pistons.
Today's lesson focuses on the first step: SENSE. B. How Do Sensors Work? Exploring the Scientific Principles
Let's investigate three common sensors you will likely use in your robotics projects. For each one, we will look at the scientific principle that makes it work. The Light Sensor (Light Dependent Resistor - LDR) What it Measures: Light intensity (how bright or dark it is). Scientific Principle: Photoconductivity. This is a scientific property of certain materials where their ability to conduct electricity changes when they are exposed to light. How it Works: An LDR is made of a special semiconductor material (like Cadmium Sulphide). In the dark, this material has very few free electrons, so its resistance is very high. It's difficult for electric current to flow through it. When light (photons) shines on the material, the light energy knocks electrons loose. With more free electrons, the material can conduct electricity much more easily, so its resistance drops significantly. In simple terms: More Light -> Lower Resistance Less Light (Darkness) -> Higher Resistance A microcontroller can measure this change in resistance and determine if it is bright or dark. Limits/Boundary Values: An LDR has a minimum resistance value in very bright light and a maximum resistance value in complete darkness. For example, it might range from 50 Ohms (Ω) in direct sunlight to 10,000,000 Ohms (10 MΩ) in total darkness. These are its boundary values. The Ultrasonic Distance Sensor (e.g., HC-SR04) What it Measures: The distance to an object. Scientific Principle: SONAR (Sound Navigation and Ranging). This principle involves sending out a sound wave and measuring how long it takes for the echo to return. Bats and dolphins use a similar natural method called echolocation. How it Works: The sensor has two parts: a transmitter (like a speaker) and a receiver (like a microphone). Step 1 (Transmit): The transmitter sends out a short burst of high-frequency sound (ultrasound), which humans cannot hear. It also starts an internal timer. Step 2 (Echo): The sound wave travels through the air, hits an object, and bounces back as an echo. Step 3 (Receive): The receiver detects the returning echo and immediately stops the timer. Step 4 (Calculate): The microcontroller reads the time the sound wave was travelling. Knowing the speed of sound in air (approximately 343 meters per second), it can calculate the distance. The Calculation: The time measured (`t`) is for the sound to go *to the object and back*. So, the time to reach the object is `t / 2`. The formula for distance is: `Distance = Speed × Time` Therefore, for the sensor: Distance = (Speed of Sound × Total Time) / 2