Grade 11 Computing: Signals Overview

Signal Types

• Analogue signals are continuous signals with infinite possibilities, while digital signals represent information using a pattern of bits (0s and 1s).
• Analogue signals are depicted by sine waves, whereas digital signals are represented by square waves.

Characteristics Comparison

• Analogue signals utilize a continuous range of values, making them suitable for audio and video transmission.
• Digital signals employ discrete data, making them ideal for computing and digital electronics.

Examples of Signals

• Examples of analogue signals include the human voice, natural sounds, FM radio signals, and analogue devices like temperature sensors and photocells.
• Digital signals can be found in computers, optical drives (CDs and DVDs), and electronic components like pushbuttons and LEDs.

Arduino and Signal Processing

• Arduino can process digital signals but requires digitalization to read analogue signals.
• Digitalization involves representing infinite values with finite numbers.

Analogue Output with Arduino

• Arduino generates analogue signals using Pulse Width Modulation (PWM), which uses digital pulses to create an analogue effect.
• The width of the pulse is defined by its 'on' time, and modifications to the pulse width create a perception of an analogue signal.

Duty Cycle and Frequency

• The duty cycle (D) represents the ratio of 'on time' to the time period (T), with values ranging from 0% to 100%.
• Frequency (f) is the number of complete cycles per second, measured in hertz (Hz) and is inversely related to the time period (f=1/T).

PWM Signal Generation

• The PWM signal can simulate voltages between 0V (off) and 5V (on) by adjusting the duty cycle.
• In Arduino, duty cycle values are scaled from 0 to 255, where 255 represents 100% duty cycle.
• The function analogWrite(pin#, Value) is used for generating PWM signals, where pin# is a designated pin on the Arduino.

Calculating PWM Values

• To derive the PWM value for a specific duty cycle:
  PWM Value = (desired duty cycle * 255) / 100
• Example: For 50% duty cycle, calculate PWM Value = (50 × 255)/100 resulting in approximately 127 (rounded).

Controlling LED Brightness

• LEDs can be controlled with both digitalWrite and analogWrite functions.
• The digital function sets LEDs to either fully on or off, while the analogue function allows for varying brightness levels.
• To set an LED to half brightness, use analogWrite(pin#, 127).

Practical Application

• Students will write code to manipulate the voltage across an LED to control its brightness directly from Arduino, applying concepts learned about PWM and duty cycles.

This quiz explores the key differences between analogue and digital signals, focusing on their characteristics and applications. Students will also learn how to read and generate these signals using a microcontroller-based board. Get ready to enhance your understanding of signal processing!