EG1122 chapter3 Signal conditioning methods AttenuationADC (1)

Introduction to Signal Conditioning Methods

• Signal Conditioning: The process of manipulating a signal to meet the requirements for further processing.

Topics Covered in Lecture 3

• Introduction to signal conditioning methods

• Signal conditioning method 1: Attenuation with voltage dividers

• Signal conditioning method 2: Analogue to Digital Converters (ADCs)

• Working principles and parameters of ADCs

• Different types of ADCs

• Integration of ADCs in Arduino boards and basic coding examples

Intended Learning Outcomes (ILOs)

• Understand the significance of signal conditioning methods.

• Grasp the working principle and applications of voltage dividers.

• Learn the fundamentals of ADCs including their basic functionality and important parameters.

• Familiarize with Flash and SAR ADC types and their advantages.

Signal Conditioning Methods Overview

• Signal conditioning converts signals from transducers to electrical signals usable by Digital Processing Units (DPUs).

• Key Methods:

  1. Attenuation: Utilizing voltage dividers.

  2. Analogue to Digital Conversion (ADC).

  3. Linealisation.

  4. Amplification: Using operational amplifiers (op-amps).

  5. Filtering: Employing passive and active filters.

  6. Electrical stimulus: Via Wheatstone bridges and voltage dividers.

  7. Electrical isolation.

Resistance and Resistor Values

• Resistance (R) is dependent on the shape and composition of materials.

  • Formula: R = ρ (L/A)

  • Resistance Categories:

    • Conductors: Low resistivity.

    • Semiconductors: Mid-range resistivity.

    • Insulators: High resistivity.

• Standard Resistor Values:

  • Notable values from 1Ω to 9.1MΩ with +/- 5% tolerance are often used in circuits.

Attenuation with Voltage Dividers

• Voltage Divider: Reduces input voltage via resistors.

  • Formulae:

    • V at R1 = Vin * (R2 / (R1 + R2))

    • V at R2 = Vin * (R1 / (R1 + R2))

Analogue to Digital Converters (ADCs)

• ADC: Key in interfacing analog signals with digital processors.

• Conversion Steps:

  1. Sampling.

  2. Holding: Capturing the sampled signal value.

  3. Quantizing: Assigning integer values to sampled voltages.

  4. Encoding: Converting these values to binary form.

• Key Parameters:

  • Range: Voltage levels ADC can digitize (e.g., -5V to 5V).

  • Sampling period: Time between samples.

  • Sampling frequency (fs): Must be > 2 * maximum frequency in the signal (Nyquist theorem).

  • Resolution: Represented by 2^n where n is the number of bits, determining the discrete levels achievable.

  • Quantisation Interval: The difference in outputs between two adjacent values.

Types of ADCs

• Common types:

  • Flash ADC

  • Successive Approximation Register (SAR) ADC

  • Sigma-Delta ADC

• Performance comparison:

  • Flash: High speed but low resolution.

  • SAR: Moderate speed and resolution.

  • Sigma-Delta: High resolution but lower speed.

Examples and Calculations

• Example of 8-bit ADC:

  • Range: 0 to 5V, Quantization interval: 19.5mV.

• Quantisation Error:

  • Difference between actual voltage and estimated voltage from ADC output.

Arduino Integration

• Arduino's ADC Specifications:

  • 10-bit resolution, utilizing SAR type ADC.

• Basic coding structure for reading analog inputs and controlling digital outputs.

  #define SENSOR_PIN A0
  float AnalogueRead;
  void setup() { Serial.begin(9600); pinMode(SENSOR_PIN, INPUT); } 
  void loop() { AnalogueRead = analogRead(A0); Serial.println(AnalogueRead); }