Lesson Notes By Weeks and Term v4 - SHS 2
DIGITAL ELECTRONICS
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
DIGITAL ELECTRONICS
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Physics
Class: SHS 2
Term: 2nd Term
Week: 14
Grade code: 2.3.3.LI.2
Strand code: 3
Sub-strand code: 3
Content standard code: 2.3.3.CS.1
Indicator code: 2.3.3.LI.2
Theme: ELECTRIC FIELD, MAGNETIC FIELD AND ELECTRONICS
Subtheme: DIGITAL ELECTRONICS
This page supports the lesson note with a companion video and a short classroom-ready summary.
For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.
Welcome, future engineers and scientists! Today, we are diving into a fundamental concept in digital electronics that makes all our digital devices work reliably. Think about your phone, a TV remote, or even the prepaid electricity meter at home. When you press a button, how does the device know for sure that you've pressed it? What happens when you are *not* pressing the button? The answer lies in preventing a state of confusion called a "floating input." We will learn about two simple but powerful tools—pull-up and pull-down resistors—that electronic circuits use to ensure every input has a clear, default state (either HIGH or LOW).
A. The Problem: The "Floating" Input Pin
In digital electronics, we work with two simple states: HIGH (also called '1' or Logic 1), which usually represents a positive voltage like +5V or +3.3V. LOW (also called '0' or Logic 0), which usually represents zero voltage, or Ground (GND).
Imagine a digital input pin, like on a microcontroller that reads a switch. This pin needs to know if the switch is pressed or not. When the switch is closed: The input pin is directly connected to +5V. It clearly reads HIGH. No problem here. When the switch is open: What is the input pin connected to? Nothing! It's left "floating" in the air. It's not connected to +5V, nor is it connected to Ground.
This floating pin is like a flag on a pole with no rope. The wind can blow it high or low randomly. In a circuit, electrical noise from the environment (like from nearby mobile phones or fluorescent lights) can make the pin randomly switch between HIGH and LOW. This makes the circuit unreliable and unpredictable.