What do output subsystems do, and how do microcontrollers and programming control a product?
Output devices (LEDs, lamps, buzzers, motors, solenoids, relays), driving outputs with transistors and relays, microcontrollers and programmable interface controllers, flowchart programming, and how programmable control makes products flexible and responsive.
A focused answer to Eduqas A-Level Product Design on programmable and output systems: output devices such as LEDs, buzzers, motors, solenoids and relays, driving outputs with transistors and relays, microcontrollers and programmable interface controllers, flowchart programming, and the benefits of programmable control.
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What this dot point is asking
Eduqas wants you to know the output devices in an electronic system, how they are driven by transistors and relays, and how microcontrollers (programmable interface controllers) and flowchart programming control a product. This completes the input, process, output model and explains how modern products are made flexible and responsive, so it is examined as recall, as the driver reasoning, and as a discussion of programmability.
Output devices
Driving outputs: transistors and relays
Microcontrollers and programmable control
Flowchart programming and the whole system
A microcontroller's program is often planned and written as a flowchart: a diagram of the sequence of decisions and actions using standard symbols (a terminal for start/stop, a process box for an action, a decision diamond for a yes/no test, arrows for flow). A flowchart for a night light might read: start, read the light sensor, is it dark? if yes turn the LED on, if no turn it off, then loop back. The flowchart makes the logic clear before it is coded, and it shows how the microcontroller ties the whole input, process, output system together: it reads inputs, decides in software, and drives outputs. A strong answer can sketch this loop and explain how programmable control replaces fixed wiring with flexible, updatable software, which is the modern way products are controlled.
Exam-style practice questions
Practice questions written in the style of WJEC Eduqas exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Eduqas 20204 marksExplain why a transistor or a relay is used to connect a small electronic control circuit to a high-power output such as a motor, rather than connecting the output directly.Show worked answer →
A Component 1 short-answer question. Marks for the current-handling reason and the isolation point.
A control circuit (a logic gate, microcontroller pin or comparator) can only supply a very small current, far too little to drive a motor, lamp or solenoid directly, and trying to do so would damage it. A transistor or relay acts as a switch driven by the small control signal but switching the large output current from a separate supply. A relay also gives electrical isolation between the low-power control side and the high-power (or mains) output side, which improves safety.
Award marks for the current-handling reason (the control cannot supply enough current) and, for a relay, the isolation/safety point. A common dropped mark is not explaining why the output cannot be driven directly.
Eduqas 20216 marksDiscuss the advantages of using a microcontroller (a programmable interface controller) to control a product, compared with a fixed circuit of separate components. Use an example to support your answer.Show worked answer →
A Component 1 extended question marked by levels of response. Reward the advantages of programmability with an example.
A microcontroller is a single programmable chip that reads inputs and controls outputs according to a program. Advantages: one cheap chip replaces many components, so the circuit is smaller, lighter and cheaper to assemble; the behaviour is set in software, so it can be changed or updated without rewiring; complex logic, timing, counting and decisions are easy; and the same hardware can do many jobs. For example, a washing machine controller runs different programmes from one chip.
Drawbacks to weigh: it needs programming skill and a programmer, and it can be overkill for a very simple task. A top answer explains the advantages (fewer parts, flexible software, complex control), gives an example, weighs the drawbacks, and concludes that programmable control suits products needing flexible or complex behaviour.
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Sources & how we know this
- Eduqas A Level Design and Technology specification (Product Design) — Eduqas (2017)