Electronic Systems Application and Selection | B3.4

Students must be able toAnalyse simple electronic products and circuits to identify the main component parts that enable them to perform a specific function.

The Input–Process–Output (IPO) model is the fundamental framework for understanding any electronic system. It breaks a complex product into three stages:

• Input: sensors detect changes in the environment (light, temperature, pressure, motion, sound, user commands) and convert them into electrical signals for the process stage.
• Process: a microcontroller, logic circuit, or embedded processor receives input signals, applies a programmed algorithm, and decides what to do next.
• Output: actuators, displays, speakers, motors, or relays respond, communicating information to a user or physically controlling the environment.

Electronics are now embedded in almost every product category: home appliances (refrigerators, washing machines, microwaves), entertainment (TVs, game consoles), communication (smartphones, computers), automotive (engine control units, GPS, advanced driver assistance), and personal wearables (smartwatches, fitness trackers). When analysing a product, the first task is to identify which components serve which stage of the IPO model.

Students must be able toDescribe how to use basic electronic measuring apparatus, including multi-meters on voltage, current and resistance ranges, and oscilloscopes to observe waveforms.

Choosing the right instrument (and connecting it correctly) is as important as the measurement itself. Using a current meter in parallel, for example, will short-circuit the component and may destroy the meter.

Digital multimeter (DMM), the most versatile handheld instrument:

• Voltage: connect in parallel across the component. No circuit interruption needed.
• Current: connect in series: the circuit must be broken and the meter inserted into the path so current flows through it.
• Resistance: the component must be removed from the circuit entirely, then connected to the meter's Ω terminals. The meter applies its own small current and measures the voltage drop.

Digital storage oscilloscope (DSO): visualises voltage waveforms over time (voltage on Y-axis, time on X-axis). Indispensable for diagnosing: ringing (damped oscillations indicating impedance problems), distorted rising edges (slow component or excessive capacitance), and amplitude problems (incorrect voltage levels indicating a faulty supply). A multimeter cannot reveal any of these: it only shows a single numerical value.

Function generator: produces test signals (sine, square, triangle waves) at a chosen frequency. Frequently used alongside a DSO: the generator provides a known input, the DSO captures the circuit's response.

Clamp meter: measures current without breaking the circuit by clamping around the conductor. For AC it uses a current transformer; for DC it uses the Hall effect (detecting the magnetic field produced by the current).

Other instruments: Megohmmeter (tests insulation resistance at high voltage: a downward trend indicates insulation breakdown); Wattmeter (measures real power P = VI); LCR meter (measures inductance, capacitance and resistance using AC test signals); Logic analyser (captures multiple digital signals simultaneously to debug timing and decode communication protocols such as I²C, SPI, UART).

Interactive Tool

Macropad Builder

Plan the switches, wiring and components for a real macropad, then generate downloadable code to build it with an ESP32.

Students must be able toCalculate power, voltage, current and resistance in a circuit, considering V = IR and P = VI by rearranging equations and substituting values.

Ohm's law: the voltage across a component equals the current through it multiplied by its resistance.

V = I × R    →    I = V / R    →    R = V / I

Power formulas: electrical power is the rate of energy conversion. Three equivalent forms:

P = V × I    =    I² × R    =    V² / R

Use whichever form avoids an intermediate calculation step. If you know V and R but not I, use P = V²/R directly rather than calculating I first.

Single-phase vs three-phase power:

• Single-phase: one AC waveform (one active wire). Used in homes and small businesses. Voltage rises and falls to zero twice per cycle, producing a momentary dip in power.
• Three-phase: three AC waveforms staggered 120° apart (three active wires). Used in industrial settings. The phases combine so that total power delivery is constant: one phase is always near its peak. More efficient for large motors and high-power equipment.

IEC 60309 industrial plug colour coding: yellow = 100–130 V, blue = 200–250 V, red = 380–480 V. Colour coding prevents incorrect connection of equipment to incompatible voltages.

Worked examples

Students must be able toCalculate resistance and capacitance in series and parallel in a circuit.

Resistors in series: total resistance is the sum of all resistors. Current is the same through each.

R_total = R₁ + R₂ + R₃ + …

Resistors in parallel: total resistance is always less than the smallest individual resistor. Voltage is the same across each; current splits between branches.

1 / R_total = 1/R₁ + 1/R₂ + 1/R₃ + …    (for equal R: R_total = R / n)

RC circuits: a resistor (R) and capacitor (C) together create time-dependent behaviour. The capacitor charges through the resistor; the time constant τ = R × C (in seconds when R is in Ω and C is in Farads) determines how quickly voltage rises or falls.

Low-pass filter: resistor in series, capacitor in parallel with the output. Passes low-frequency (slow) signals; attenuates high-frequency (fast) signals. The capacitor charges slowly, smoothing rapid fluctuations.

High-pass filter: capacitor in series, resistor in parallel with the output. Blocks low-frequency signals (capacitor blocks DC and very slow signals); passes high-frequency signals.

Contact bounce (chatter) elimination: when a mechanical switch closes, the contacts bounce and produce multiple rapid 1s and 0s before settling. A low-pass RC filter smooths this leading edge, so the logic gate receives a clean single transition rather than a burst of false triggers.

Worked examples (resistor networks)

For combination circuits, always resolve the parallel branches first, then add the series elements, just as you would apply BODMAS to arithmetic.

Students must be able toConstruct flow diagrams (using appropriate symbols) to model a programmable system that controls an electronic device.

A flow diagram (flowchart) maps the sequence of steps in an algorithm using standardised symbols. In electronics, flowcharts are used to plan and communicate how a microcontroller will respond to inputs.

Standard flowchart symbols:

• Terminator (rounded rectangle or oval): marks the Start or End of the program.
• Process (rectangle): a calculation or action (e.g., "Turn fan ON", "Increment counter").
• Input / Output (parallelogram): data entering or leaving the system (e.g., "Read temperature sensor", "Display value on LCD").
• Decision (diamond): a yes/no branch based on a condition (e.g., "Temperature > 30°C?"). Two paths exit: one for Yes, one for No.

Flow diagrams are useful before writing code because they separate the logic of what the system must do from the syntax of how to code it. A well-drawn flowchart can be translated directly into any programming language.

Students must be able toConstruct diagrams for simple circuits that use resistors, capacitors, switches, relays, diodes, transistors, operational amplifiers, integrated circuits, and input and output devices.

Designers use different diagram types depending on the level of detail needed and the audience for the drawing:

• Block diagram (functional diagram): shows the major subsystems of a product and how they connect at a high level. No component values or symbols: just labelled boxes and arrows. Used to plan and explain system architecture before designing circuits.
• Circuit diagram (schematic): shows every component and its logical connection using standardised symbols (resistor, capacitor, switch, diode, transistor, relay, op-amp, IC). Values are specified. Used by engineers to build, troubleshoot and modify circuits.
• Logic diagram: shows the arrangement of logic gates (AND, OR, NOT) and their interconnections. Used to represent the decision-making or processing stage of a digital system.
• Flow diagram: as described in 3.4.5, maps the program algorithm. Not a circuit diagram; it represents behaviour, not physical connections.

All four types are used in IB assessment. Block and flow diagrams are expected at a conceptual level; circuit and logic diagrams require correct use of standard symbols.

Mapping a Smoke Detector

One tiny circuit, four completely different diagrams.

Read case study →

Students must be able toDetermine the use of sensors to collect and input information into a digital system, including accelerometer (motion), ultrasonic (distance or proximity), photoresistor (light), voltage (moisture), hygrometer (humidity and air temperature), pressure (barometric), microphone (sound) and infrared (radiation or heat).

Sensors are the input stage of the IPO model: they convert a physical quantity into an electrical signal that a microcontroller can read. The choice of sensor must match the physical quantity being measured and the output format the processor expects (analog voltage, or digital signal).

Students must be able toCreate simple circuits that use microcontrollers as a programmable integrated circuit (PIC) with appropriate software to carry out a predetermined task.

An embedded system is a dedicated computer system designed to perform a specific function within a larger product. Unlike a general-purpose computer, it runs one fixed program stored in its memory.

The heart of the process stage is a microcontroller (MCU), also referred to as a programmable integrated circuit (PIC). A microcontroller integrates on a single chip:

• A processor: executes the program instructions
• Flash memory (ROM): stores the program permanently
• RAM: holds variables and data during operation
• Digital I/O pins: read digital sensors and control digital outputs
• Analog inputs (ADC): convert analog sensor voltages to digital values
• Timers, PWM outputs, and communication interfaces (I²C, SPI, UART) for interacting with other components

Educational platforms such as Arduino (AVR/ARM microcontrollers) and Raspberry Pi (single-board computer) make it accessible to prototype embedded systems. In industry, dedicated MCUs (e.g., STM32, PIC, ATmega) are chosen for their size, power consumption and cost.

Students must be able toDescribe digital systems in terms of the binary number system, Boolean algebra, logic gates (AND, OR and NOT), combinational logic circuits and sequential logic circuits, and construct truth tables for a digital circuit.

All digital systems represent data using binary: a base-2 number system using only 0 and 1 (off and on). Multiple binary digits (bits) represent larger values: 8 bits = 1 byte, capable of representing 256 values (0–255).

Boolean algebra defines how binary values are combined using logical operations. Three fundamental gates:

• AND (A · B): output is 1 only when both inputs are 1. Used for conditions that must all be true simultaneously.
• OR (A + B): output is 1 when at least one input is 1. Used when any one of several conditions triggers an output.
• NOT (Ā): inverts the input: 0 becomes 1, 1 becomes 0. Used to reverse a condition.

A truth table lists every possible combination of inputs and the corresponding output. For n inputs there are 2ⁿ rows.

Combinational logic: the output depends only on the current inputs. No memory: the same input always produces the same output. Examples: AND, OR, NOT, NAND, NOR, XOR gates.

Sequential logic: the output depends on current inputs AND previous states. Uses memory elements (flip-flops). Examples: counters, registers, state machines: the basis of most microcontrollers.

Truth tables (AND, OR, NOT)

Students must be able toDetermine appropriate output devices to communicate information or physically control an environment, including motors (including servos and pumps), LCD display, buzzer and relay.

Output devices are the third stage of the IPO model: they convert the processed electrical signal into a physical action or visible/audible communication.

When selecting an output device, consider three things: the type of action needed (motion, information, sound), the voltage and current required by the device, and whether the microcontroller can drive it directly or needs an amplifying component (transistor, relay, or motor driver IC).

Students must be able toCompare the protocol embedded systems used to communicate with other systems (Wi-Fi vs Bluetooth vs 5G).

Embedded systems often need to communicate with other devices or networks. The choice of wireless protocol depends on range, speed, power consumption and the infrastructure available.

Bluetooth: designed for low-power, short-range device-to-device communication. Operates at 2.4 GHz using frequency hopping to reduce interference. Typical range: ~10 m. Uses a layered protocol stack: the Controller layer (Radio, Link Manager, Voice CODEC) communicates with the Host layer (GAP, GATT, ATT, SMP, RFCOMM) via the HCI interface. GAP (Generic Access Profile) governs device discovery and connection setup. Used in: wireless earbuds, keyboards, fitness trackers, medical devices.

Wi-Fi: high-speed, medium-range local area network access. Connects devices to a router (and thus the internet). Higher power consumption than Bluetooth. Range: ~50 m indoors. Used in: laptops, smart home devices, IP cameras.

5G: fifth-generation cellular technology. Offers ultra-high data speeds, ultra-low latency, and the ability to connect massive numbers of devices simultaneously. Does not require a local router: connects directly to the cellular network. Used in: autonomous vehicles, smart cities, large-scale IoT deployments.

Case study (Australia's 3G shutdown, October 2024): Many 4G phones were designed to fall back to 3G for voice calls because 4G voice required a separate technology called VoLTE (Voice over LTE). When Australia's ACMA shut down the 3G network, non-VoLTE phones lost all voice capability, including emergency calls. Even medical alarms and personal emergency response devices stopped working. The lesson for embedded systems designers: never assume that legacy infrastructure will remain available. Design for forward compatibility and include graceful upgrade paths.