A3.4 / Introduction to Electronic Systems 

An electronic system is a set of interacting components designed to achieve a specific goal, typically involving the manipulation of electrical signals or data.

All electronic systems can be described in terms of four functional stages:

• Input: The component that gathers information or data from the outside world (e.g., a sensor, switch, or keyboard).

• Process: The component that interprets, calculates, or manipulates the input data based on programmed instructions (e.g., a microcontroller or processor).

• Output: The component that translates the processed information back into an action or display for the user or environment (e.g., an LED, speaker, or motor).

A feedback loop is the signal path from the output back to the input, allowing the system to check and adjust its performance relative to a desired state (e.g., a thermostat using a temperature sensor to check if the heater output achieved the set temperature).

Analogue and digital are the two main ways that electronic systems represent, process, and transmit information (signals).

Designers use SI Multipliers to manage the large range of values encountered in electronics:

• Mega (M), 10^6: A resistance of 1 MΩ (Megaohm) is 1,000,000 Ohms.

• Kilo (k), 10^3: A resistor value of 5 kΩ (Kiloohm) is 5,000 Ohms.

• Milli (m), 10^{-3}: A small current could be 100 mA (milliampere), which is 0.100 Amperes.

• Micro (μ), 10^{-6}: A capacitor might have a value of 10μF (microfarad).

• Nano (n), 10^{-9}: An even smaller capacitor value is 20 nF (nanofarad).

• Giga (G), 10^9: Modern microprocessors operate at speeds often measured in GHz (Gigahertz).

Electronic systems achieve their specific function through the interaction of various components, categorized broadly as passive (components that do not introduce power gain) and active (components capable of power gain or control). Understanding the specific purpose of each component is vital for system design and analysis.

Passive Electronic Components

Passive components control the flow and storage of energy within a circuit.

• Fixed Resistors:

  • Limit the flow of electrical current and to divide voltage in a circuit. They have a specific, unchanging resistance value (measured in Ohms, Ω).

• Variable Resistors (Potentiometers and Rheostats):

  • Provide a changeable resistance that can be adjusted manually (e.g., volume control in audio equipment) or by environmental factors (e.g., LDRs changing resistance based on light).

• Capacitors:

  • Store electrical energy in an electric field. They are used for filtering out noise (smoothing voltage), coupling signals, and timing circuits (measured in Farads, F).

• Switches:

  • Make or break an electrical connection (open or close a circuit) to control the flow of current manually.

• Relays:

  • An electrically operated switch. They use a low-power control signal to switch a much higher-power circuit, providing electrical isolation between the control signal and the high-power load.

Active Electronic Components

Active components can control the flow of current, introduce power gain, and perform complex logic operations.

• Diodes:

  • Purpose: To allow electric current to flow effectively in only one direction. They are fundamental for converting alternating current (AC) into direct current (DC) in power supplies (rectification). A Light-Emitting Diode (LED) is a special type that produces light.

• Transistors:

  • Purpose: As the most fundamental active component, a transistor acts primarily as an electronic switch or a signal amplifier. A small current or voltage applied to one terminal controls a much larger current flowing through the other two, enabling all modern digital logic and amplification circuits.

Input devices act as the sensing element of an electronic system. Their role is to identify a change in the environment and convert that physical change into a usable electrical signal for the processing unit. They are categorized as either digital or analogue.

Digital Input Components (Switches)

Digital inputs have only two discrete states: ON or OFF (High or Low). They signal a binary state change.

• Switches: Used to make or break an electrical connection based on a physical action. They provide a clear, binary (0 or 1) signal to the processing stage.

Analogue Input Components (Sensors)

Analogue inputs produce a continuously variable and proportional output signal in response to a physical quantity.

• Light Sensor (e.g., LDR): Measures the intensity of ambient light. Its resistance changes smoothly as light level changes.

• Temperature Sensor (e.g., Thermistor): Measures the heat level of the environment. Its resistance or voltage output changes continuously with temperature.

• Humidity Sensor: Measures the amount of water vapor in the air. Its electrical output changes continuously as relative humidity fluctuates.

• Sound Sensor (e.g., Microphone): Measures vibrations/pressure waves (sound). It converts sound waves into a fluctuating, continuous analogue electrical voltage.

Processing devices form the central control unit of any electronic system, taking the electrical signal from the input stage and manipulating it according to design requirements to drive the output stage. Processing functions are categorized based on whether they handle continuous analogue signals or discrete digital data.

Analogue Processing: Signal Conditioning

Analogue processing involves maintaining the continuous nature of a signal while modifying its characteristics, such as strength or quality.

• Signal Conditioning: This term describes a necessary process used to prepare a raw analogue input signal (e.g., from a temperature sensor) so that it is suitable for either direct use by an analogue output or for conversion by a digital component (ADC).

• Function: Signal conditioning typically involves:

  • Amplification: Increasing the signal's magnitude (voltage or current) if the raw signal is too weak.

  • Filtering: Removing unwanted noise or frequency components from the signal to improve clarity.

  • Buffering: Isolating the input stage from the processing stage to prevent the latter from interfering with the former.

• Components: Operational Amplifiers (Op-Amps) and filters built from resistors and capacitors.

Digital Processing: Program Control

Digital processing works with discrete values (binary 0s and 1s) and is fundamentally about decision-making, logic, and sequential operations.

• Program Control: This refers to the ability of a digital circuit to execute a sequence of stored instructions (a program) to determine the output based on current and historical inputs.

• Function: Program control involves:

  • Logic Operations: Using gates (AND, OR, NOT) to make decisions (e.g., turn a light on only if it is dark and a motion sensor is triggered).

  • Timing: Using clocks and counters to ensure actions occur in the correct sequence and duration.

  • Data Manipulation: Performing calculations or moving data using memory.

• Components: Microcontrollers (MCUs), Microprocessors, and various Logic Gates (ICs).

Output devices, or actuators and indicators, form the final stage of an electronic system. They take the processed electrical signal and convert that energy back into a usable physical change—such as light, motion, sound, or a display—to fulfill the system's function. They are classified based on whether they require a continuous (analogue) signal or a discrete (digital) signal to operate.

Digital Output Components (Discrete Action)

Digital outputs are activated by simple ON/OFF signals (binary 1 or 0) from the processing unit.

• Lights/Light-Emitting Diode (LED): Used for visual indication (e.g., power status or warnings). An LED switches ON when current flows and OFF when it stops.

• Buzzers: Used to provide audio feedback or an alarm using a simple ON/OFF tone.

• Relays: Function as an electrically operated switch, allowing a low-power control signal from the processor to switch a much higher-power external circuit (e.g., turning on a large motor).

• Liquid Crystal Display (LCD) / Braille Display: These are display devices that receive digital data streams (e.g., character codes or pixel maps) to present visual or tactile information.

Analogue Output Components (Variable Action)

Analogue outputs require a continuous, variable electrical signal to control their function, resulting in a proportional physical effect.

• Motors: Convert electrical energy into mechanical rotational motion. The speed and direction of the motor are typically controlled by varying the voltage or current (an analogue action).

• Speakers / Headphones: Convert the fluctuating electrical signal (representing sound waves) back into audible sound (vibrations in the air). The volume and frequency are determined by the analogue properties of the signal.

• Haptic Devices: Create tactile feedback (e.g., vibrations in a phone or controller). The intensity of the vibration is often controlled by an analogue signal.

• Printers / Plotters: Complex devices that translate digital data from the processor into physical output (text or graphics on paper). While the data is digital, the movement of the motors and the intensity of the print head mechanisms are precisely controlled via analogue principles.

An operational amplifier (op-amp) is a versatile, active IC that is a core building block of analogue circuits. It is a high-gain voltage amplifier with two inputs (differential) used to control voltage signals.

Common Applications of Op-Amps

The op-amp's main role is analogue signal conditioning—preparing weak signals for the processing stage.

• Analogue Signal Amplification: Op-amps are primarily used to amplify the very weak voltage signals produced by sensors (e.g., temperature, light). This amplified signal is strong enough for the digital microcontroller's Analogue-to-Digital Converter (ADC) to read accurately.

• Digital Signal Amplifiers (Comparator): An op-amp can be configured as a voltage comparator. It compares two input voltages and outputs a simple High or Low signal, effectively converting an analogue value into a digital decision (e.g., turning a light on when a certain voltage threshold is crossed).

Op-Amps in IoT Home Appliances

In Internet of Things (IoT) home appliances (like smart coffee makers or environmental sensors), op-amps are essential for reliable sensing.

• Sensor Interfacing: In a smart thermostat, an op-amp amplifies the minute voltage change from the temperature sensor.

• Noise Reduction: They are used as active filters to eliminate electrical noise picked up by long sensor cables, ensuring the data received by the digital processor is clean and accurate.

An embedded system is a specialized computer system designed to perform one or a few dedicated functions, often in real-time, within a larger mechanical or electronic device. Unlike a general-purpose computer (like a laptop), an embedded system is integrated into the product it controls and is not easily programmable by the end-user. It typically consists of a microcontroller or microprocessor, along with the necessary memory and dedicated input/output peripherals.

Role in Augmenting Everyday Products

Embedded systems are responsible for providing the "smart" functionality found in almost every modern consumer product. Their implementation augments products in three key ways:

1. Functionality: They add features that discrete logic circuits cannot provide. For example, in a modern car, embedded systems manage everything from the anti-lock braking system (ABS) to navigation, significantly enhancing the vehicle's core capabilities.

2. Efficiency: They optimize the operation of a product, reducing power consumption and resource use. In an inverter air conditioner, an embedded system precisely monitors room temperature and adjusts the compressor speed incrementally, consuming far less power than a traditional ON/OFF unit.

3. Automation: They allow the product to perform complex tasks automatically based on sensed data without continuous human intervention. For instance, a smart camera uses an embedded system to perform image recognition and automatically track a subject or send alerts when motion is detected.

The fundamental role of embedded systems is to allow different digital (and analogue) parts of a device to communicate and cooperate to perform a specific, complex task with high reliability and minimal resources.

An electronic circuit is an assembly of components interconnected to perform a specific function. This complex assembly is universally represented by a circuit diagram, which is a stylized, two-dimensional graphical representation of the actual circuit.

Purpose and Use of Circuit Diagrams

Circuit diagrams are essential tools for designers, engineers, and technicians, as their primary function is to communicate the operational principles and connectivity of an electronic system, rather than its physical layout.

• Communication: Diagrams use standardized symbols recognized internationally. This ensures that any engineer, regardless of native language, can understand the circuit's function and components.

• Analysis and Debugging: They allow for the systematic analysis of the circuit's behavior, particularly the signal flow and logical sequence. When a circuit malfunctions, the diagram is used to trace connections and identify faulty components, greatly simplifying the debugging process.

• Design and Planning: Diagrams are the blueprint for the design process. They are used to plan the integration of components (such as fixed and variable resistors, diodes, and microcontrollers) before a physical prototype is built, ensuring the desired function is achievable.

• Documentation: They serve as official documentation for manufacturing, maintenance, and future modifications of the electronic product.

The Role of Symbols

The specific symbols used for components (resistors, transistors, op-amps, etc.) act as a universal language. Each symbol represents the electrical function of the component, not its physical appearance. This allows the designer to focus solely on the flow of power and information when mapping out the circuit, making the diagram a clear, concise tool for functional representation.