Electronic Systems Application and Selection | B3.4

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.

输入-处理-输出（IPO）模型是理解任何电子系统的基本框架。它将复杂产品分解为三个阶段：

• 输入——传感器检测环境变化（光、温度、压力、运动、声音、用户指令），并将其转换为电信号供处理阶段使用。
• 处理——微控制器、逻辑电路或嵌入式处理器接收输入信号，执行编程算法，并决定下一步操作。
• 输出——执行器、显示器、扬声器、电机或继电器作出响应——向用户传递信息或对环境进行物理控制。

电子系统现已嵌入几乎所有产品类别：家用电器（冰箱、洗衣机、微波炉）、娱乐设备（电视、游戏机）、通信工具（智能手机、计算机）、汽车（发动机控制单元、GPS、高级驾驶辅助）和可穿戴设备（智能手表、健身追踪器）。分析产品时，第一步是识别哪些组件属于IPO模型的哪个阶段。

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).

选择正确的仪器并正确连接与测量本身同样重要。例如，将电流表并联连接会使元件短路，并可能损坏仪表。

数字万用表（DMM）——最通用的手持仪器：

• 电压：与被测元件并联，无需断开电路。
• 电流：串联接入——需要断开电路并将仪表插入电路中，使电流流过仪表。
• 电阻：需将元件从电路中完全拆除，再连接到仪表的Ω端子。仪表通过内部小电流测量电压降来计算电阻值。

数字存储示波器（DSO）——随时间可视化电压波形（Y轴为电压，X轴为时间）。用于诊断：振铃（阻抗问题导致的阻尼振荡）、上升沿失真（元件缓慢或电容过大）和幅度异常（电压电平不正确，提示电源故障）。万用表无法揭示这些问题——它只能显示单一数值。

函数发生器——产生指定频率的测试信号（正弦波、方波、三角波）。常与示波器配合使用：发生器提供已知输入，示波器捕捉电路响应。

钳形表——无需断路即可测量电流，通过夹住导线来检测其周围的磁场。交流使用电流互感器；直流使用霍尔效应。

其他仪器：兆欧表（在高电压下测试绝缘电阻——数值下降趋势表明绝缘劣化）；功率计（测量实际功率P = VI）；LCR表（用交流信号测量电感、电容和电阻）；逻辑分析仪（同时捕捉多路数字信号，调试时序并解码通信协议）。

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.

欧姆定律：元件两端的电压等于通过它的电流乘以其电阻。

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

功率公式：电功率是能量转换的速率。三种等效形式：

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

选择能减少计算步骤的公式。若已知V和R但不知I，直接用P = V²/R，而无需先计算I。

单相电与三相电：

• 单相电——一个交流波形（一根火线）。用于家庭和小型企业。电压每个周期两次降至零，产生瞬时功率下降。
• 三相电——三个相位相差120°的交流波形（三根火线）。用于工业场合。三相叠加使总功率持续稳定——始终有一相接近峰值。对大型电机和大功率设备更高效。

IEC 60309工业插头颜色编码：黄色=100–130V，蓝色=200–250V，红色=380–480V。颜色编码防止设备连接到不兼容的电压。

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.

串联电阻——总电阻为所有电阻之和。每个电阻通过的电流相同。

R_total = R₁ + R₂ + R₃ + …

并联电阻——总电阻始终小于最小的单个电阻。每个电阻两端电压相同；电流在各支路间分配。

1 / R_total = 1/R₁ + 1/R₂ + 1/R₃ + …   （相等时：R_total = R / n）

RC电路——电阻（R）和电容（C）共同产生时间依赖的行为。电容通过电阻充电；时间常数τ = R × C（R单位Ω，C单位F时，τ单位为秒）决定电压上升或下降的速度。

低通滤波器：电阻串联，电容与输出并联。通过低频（慢速）信号；衰减高频（快速）信号。电容缓慢充电，平滑快速波动。

高通滤波器：电容串联，电阻与输出并联。阻断低频信号（电容阻断直流和极慢信号）；通过高频信号。

消除触点弹跳（抖动）：机械开关闭合时，触点在稳定前会多次弹跳，产生一系列快速的1和0。低通RC滤波器平滑这一前沿信号，使逻辑门接收到干净的单一跳变，而非一连串误触发。

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.

流程图使用标准化符号描述算法的步骤序列。在电子学中，流程图用于规划和传达微控制器如何响应输入。

标准流程图符号：

• 圆角矩形（椭圆）——起止框：标记程序的开始或结束。
• 矩形——处理框：计算或操作（如"开启风扇"、"计数器加1"）。
• 平行四边形——输入/输出框：数据进入或离开系统（如"读取温度传感器"、"在LCD上显示数值"）。
• 菱形——判断框：基于条件的是/否分支（如"温度 > 30°C？"）。有两条出路：是和否。

在编写代码之前先画流程图非常有用，因为它将系统的逻辑（做什么）与编程语法（如何编写）分开。一张绘制良好的流程图可以直接翻译成任何编程语言。

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.

设计师根据所需的详细程度和目标受众使用不同类型的图：

• 框图（功能图）——在高层面上显示产品的主要子系统及其连接方式。不含元件数值或符号——仅有带标注的方框和箭头。在设计电路之前用于规划和解释系统架构。
• 电路图（原理图）——使用标准化符号（电阻器、电容器、开关、二极管、晶体管、继电器、运算放大器、集成电路）显示所有元件及其逻辑连接，并标注数值。工程师用其搭建、排查和修改电路。
• 逻辑图——显示逻辑门（与、或、非）的排列及其连接方式。用于表示数字系统的决策或处理阶段。
• 流程图——如3.4.5所述，描述程序算法。这不是电路图——它表示行为，而非物理连接。

IB评估中使用所有四种类型。框图和流程图在概念层面上考查；电路图和逻辑图需要正确使用标准符号。

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).

传感器是IPO模型的输入阶段——它们将物理量转换为微控制器可读取的电信号。传感器的选择必须匹配被测物理量以及处理器所需的输出格式（模拟电压或数字信号）。

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.

嵌入式系统是专为在更大产品中执行特定功能而设计的专用计算机系统。与通用计算机不同，它运行存储在内存中的固定程序。

处理阶段的核心是微控制器（MCU），也称为可编程集成电路（PIC）。微控制器在单芯片上集成了：

• 处理器——执行程序指令
• 闪存（ROM）——永久存储程序
• RAM——在运行期间保存变量和数据
• 数字I/O引脚——读取数字传感器并控制数字输出
• 模拟输入（ADC）——将传感器模拟电压转换为数字值
• 定时器、PWM输出和通信接口（I²C、SPI、UART），用于与其他组件交互

Arduino（AVR/ARM微控制器）和Raspberry Pi（单板计算机）等教育平台让嵌入式系统原型开发变得更加容易。在工业中，专用MCU（如STM32、PIC、ATmega）因其尺寸、功耗和成本而被选用。

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.

所有数字系统都使用二进制表示数据——一种仅使用0和1（关和开）的二进制数系统。多个二进制位（比特）表示更大的值：8位=1字节，能表示256个值（0–255）。

布尔代数定义了如何使用逻辑运算组合二进制值。三种基本门：

• 与门（A · B）：仅当两个输入都为1时，输出为1。用于所有条件必须同时满足的情况。
• 或门（A + B）：当至少一个输入为1时，输出为1。用于任何一个条件触发输出的情况。
• 非门（Ā）：反转输入——0变为1，1变为0。用于反转条件。

真值表列出所有可能的输入组合及其对应输出。n个输入有2ⁿ行。

组合逻辑：输出仅取决于当前输入。无记忆——相同输入始终产生相同输出。例：与、或、非、与非、或非、异或门。

时序逻辑：输出取决于当前输入和之前状态。使用记忆元件（触发器）。例：计数器、寄存器、状态机——大多数微控制器的基础。

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

输出设备是IPO模型的第三阶段——将处理后的电信号转换为物理动作或可见/可听的通信。

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.

嵌入式系统通常需要与其他设备或网络通信。无线协议的选择取决于范围、速度、功耗和可用基础设施。

蓝牙——专为低功耗、短距离设备间通信设计。在2.4 GHz频段使用跳频技术减少干扰。典型范围：约10米。使用分层协议栈：控制器层（无线电、链路管理器、语音编解码器）通过HCI接口与主机层（GAP、GATT、ATT、SMP、RFCOMM）通信。GAP（通用访问配置文件）负责设备发现和连接建立。应用于：无线耳机、键盘、健身追踪器、医疗设备。

Wi-Fi——高速、中距离局域网络访问。将设备连接到路由器（进而连接互联网）。功耗高于蓝牙。室内范围约50米。应用于：笔记本电脑、智能家居设备、IP摄像头。

5G——第五代蜂窝技术。提供超高数据速度、超低延迟，以及同时连接大量设备的能力。不需要本地路由器——直接连接到蜂窝网络。应用于：自动驾驶汽车、智慧城市、大规模物联网部署。

案例研究——澳大利亚3G网络关闭（2024年10月）：许多4G手机被设计为回落到3G进行语音通话，因为4G语音需要一种名为VoLTE（基于LTE的语音通话）的独立技术。当澳大利亚通信与媒体管理局关闭3G网络后，非VoLTE手机失去了所有语音功能——包括紧急呼叫。甚至医疗警报和个人紧急响应设备也停止工作。对嵌入式系统设计师的启示：永远不要假设遗留基础设施将持续可用。应为前向兼容性而设计，并提供优雅的升级路径。