Electronic and Pneumatic Control
AdvancedControl can be mechanical, electrical, electronic or pneumatic: batteries, switches, sensors, LEDs and relays build electronic control, while cylinders and directional valves turn compressed air into action. When building systems, safety measures always come first.
- Control tasks can be realised mechanically, electrically, electronically or pneumatically
- Electrical components carry and act; electronic components sense and judge
- Series circuits stop everywhere when one link breaks; parallel branches run alone; LEDs need limiting resistors
文體小知識：科技知識說明文逐一介紹元件的功能與電路原理，配合安全守則與設計流程，令讀者能建構簡單控制系統。
§Text Passage
1One control task, several technologies: mechanical, electrical, electronic or pneumatic — the engineer's craft lies in choosing well. Electronics excels at sensing and judging, pneumatics at exerting force, and the two often cooperate: sensors gather information, control circuits decide, cylinders or motors act — together forming a complete automation system.
2Each entry-level electronic component has its craft: resistors limit current, light-emitting diodes signal status, light-dependent resistors and thermistors sense light and temperature, relays let small currents command large ones. Circuit theory is equally plain: current needs a complete loop; series offers one path, parallel gives each branch independence — the pattern of every home's wiring.
3Pneumatic systems draw power from compressed air, routed by directional valves to push pistons in strong, crisp strokes. Bus doors and factory grippers often move by cylinder. Air is free, harmless when it leaks, and so pneumatics is a fixture of industrial automation — its price being the compressible air that limits fine positioning.
4When building control systems, safety comes before everything: low-voltage supplies and disconnected wiring for electronics; locked fittings, rated pressure and exhaust pointed away for pneumatics; emergency stops reserved for computer control. Design with the input–process–output frame, draw the blocks, then choose parts block by block. With these methods, your ideas can become working creations — safely.
1Summary 重點摘要
Control can be mechanical, electrical, electronic or pneumatic: batteries, switches, sensors, LEDs and relays build electronic control, while cylinders and directional valves turn compressed air into action. When building systems, safety measures always come first.
2Vocabulary cards Vocabulary
Parts that carry current and act, such as batteries, switches and motors.
Parts that sense, judge and process signals, such as resistors and relays.
The complete path that current flows around.
Components chained in one path, with a single route for current.
A component that glows when current flows forward, often a status indicator.
A sensor whose resistance changes with light level.
A sensor whose resistance changes with temperature.
An electromagnetic switch in which a small current controls a large one.
Technology that uses compressed air as its power.
An actuator where compressed air drives a piston to push in a line.
3Step by step Steps
- Four ways to controlOne control task can be realised in several technologies, commonly four: mechanical control through levers and cams; electrical control through motors and transmission parts; electronic control through components that process signals; and pneumatic control, where compressed air drives cylinders. Choose by force needed, response speed, environment and cost. For example, an automatic door might be foot-levered, motor-driven or cylinder-pushed; a supermarket picks a motor with a sensor for speed and easy maintenance, while factory grippers often go pneumatic for simple, powerful action.
- Basic electrical componentsElectrical components form the pathway and the muscle of a circuit: batteries or power supplies give energy; wires carry current; switches open and close the circuit; bulbs turn electricity into light; motors turn it into rotation; buzzers turn it into sound. Together they form the simplest control outputs. For example, a torch circuit already holds battery, switch, wires and bulb; swap the bulb for a motor and it drives a small fan or a model car — the embryo of a control task.
- Basic electronic components and sensingElectronic components let a circuit sense and judge: resistors limit current and protect parts; light-emitting diodes glow only when current flows forward, serving as status indicators; light-dependent resistors drop their resistance in bright light, thermistors change with temperature — the everyday sensors; relays use a small current to switch a large one, letting a weak signal command motors and other power devices. For example, an automatic night light uses a light-dependent resistor to sense the room: darkness raises resistance and triggers the lamp, dawn switches it off — automatic, with no hand needed.
- Simple circuit theoryCurrent flows only in a complete loop: from the positive terminal through components back to the negative — break anywhere and it stops. In a series circuit the parts chain into one path, so one failed bulb stops everything; in a parallel circuit each branch runs independently, which is why home appliances are wired in parallel — switching off the TV never stops the fridge. A light-emitting diode must be paired with a suitable series resistor or excess current destroys it. For example, old series-wired fairy lights died wholesale when one bulb failed; parallel sets keep the rest glowing.
- An introduction to pneumaticsPneumatic systems use compressed air as power: a compressor pressurises, stores and filters air; pipes carry it to a directional control valve; the valve routes it to a cylinder, whose piston drives out in a forceful reciprocating stroke, giving push or pull. Pneumatics is strong, quick and simple, and leaking air pollutes nothing; its cost is the compressibility of air, which limits positioning accuracy compared with mechanical transmission. For example, the grippers on factory lines and the doors of buses are often cylinder-driven — decisive, durable action.
- Safety measures for building control systemsBuilding electronic, pneumatic and computer control systems carries strict safety measures. Electronics: experiment only at low voltage, disconnect before wiring, check insulation and polarity, never alter a live circuit. Pneumatics: lock fittings firmly, inspect before admitting air, keep pressure within component ratings, never point exhaust at anyone. Computer control: verify the program before connecting actuators and always provide an emergency stop. For example, when testing a pneumatic gripper, run it first at reduced pressure and step up only after the action proves sound — one more check is cheaper than any burst hose.
- From concept to system: designing a control schemeDesign with the input–process–output frame: define the task and what must be sensed (input); decide which components will judge and compare (process); choose how the action is performed (output); and attach safety measures to every stage. Draw the system as a block diagram with signal arrows, then select electronic or pneumatic parts block by block — the scheme gains a clear track. For example, an automatic fish feeder: a timer as input, a control circuit comparing time as process, a motor turning a feed drum as output — powered by low-voltage batteries inside a waterproof case.
5Worked example Example
Example: the family is away for the weekend and nobody will feed the fish. Design an automatic feeder's control scheme with input–process–output, listing component choices and safety measures.
- Input → a timer or real-time clock module that fires a trigger signal at preset times, twice daily
- Process → an electronic control circuit receives the signal, compares it with the setting and issues a short start command
- Output → a motor turns the feed drum, dropping a measured portion onto the water; an LED flashes to confirm feeding
- Safety measures → low-voltage battery power, waterproof casing fixed to the tank lid, wires kept off the water, a covered drum opening to keep feed dry
- Answer: The scheme pairs a timer input, an electronic circuit process and a motor-and-drum output — a simple open loop: feeding needs no sensing or correction, so timed portions meet the task cheaply and reliably. For finer control, add a light-dependent resistor so feeding happens only in daylight, or a counter to block repeated triggers. Safety rests on low-voltage batteries, waterproofing and dry wiring, so the device sits safely above the tank. The lesson: define the task's needs first, then choose the control technology and components — the design then follows naturally.
6Common mistakes Mistakes
7Quick check Quick check
Q1What powers a pneumatic system? A. springs B. compressed air C. electromagnets
Q2Which component lets an automatic night light sense brightness, and how does it work?
Q3Why are home appliances wired in parallel?
Q4What safety checks on connections come before operating a pneumatic device?
Q5What role does a relay play in a control system?
8Recap Recap
- Control tasks can be realised mechanically, electrically, electronically or pneumatically
- Electrical components carry and act; electronic components sense and judge
- Series circuits stop everywhere when one link breaks; parallel branches run alone; LEDs need limiting resistors
- Pneumatics drives cylinders with compressed air — strong, fast, simple
- Safety first: low-voltage supply, disconnect before wiring, locked hose fittings, rated pressure