Input sends data in; output presents it out
An input device converts data from the outside world into binary and sends it into the computer (keyboard, mouse, microphone, touch screen, barcode/QR scanner, camera). An output device takes processed data from the computer and presents it in human-usable form (screen, projector, printer, speaker, actuator). Input is needed because the CPU cannot act on data it has not received; output because binary results are useless until presented to the user.
Sensor: an input device that measures
A sensor is an input device that continuously measures a physical (analogue) quantity and sends the data to a microprocessor. Sensors read conditions automatically, continuously and more accurately than a human. The 0478 syllabus lists 14 sensors (e.g. temperature, light, pH, level, gas, proximity) — see the note table for what each measures. Most give analogue output, so an ADC is needed before a digital microprocessor can use it.
Sensor + microprocessor control chain
A monitoring or control system uses a sensor and microprocessor: (1) the sensor measures the quantity; (2) the reading is digitised (ADC) and sent; (3) the microprocessor compares it with a stored pre-set value; (4a) a monitoring system displays or alarms but does not change conditions; (4b) a control system signals an actuator that changes conditions; (5) the loop repeats. Monitoring watches; control acts back on the process.
Drawn from real examiner reports.
Generic sensor + microprocessor answers
"How the sensor and microprocessor are used" answers are too generic — "the sensor sends data to the microprocessor" with no compare-to-stored-value step, no actuator action and no specific scenario. Name the sensor for the context, state the reading is compared with a pre-set value, and give the exact output action for that scenario.
November 2023 (w23) Q7(b) and June 2023 (s23): very few candidates gave a detailed, technical, context-specific response; most gave a generic description of a sensor/microprocessor system.
Wrong sensor for the context
Selection questions want the most suitable sensor for the context — a plausible-but-wrong sensor scores zero. Match the sensor to the quantity measured: soil acidity → pH (not moisture); a liquid's height → level (not infra-red); a person passing → proximity/infra-red; air quality → gas. Map the quantity word in the stem to the right sensor.
June 2023 (s23): infra-red was the most common UNSUITABLE sensor choice (level was correct). November 2022 (w22): moisture sensor wrongly chosen for soil acidity (a pH context).
Actuator is an output, not an input
An actuator is an output device — it receives a signal from the processor and produces a physical action (turning a motor, opening a valve, switching a heater). Candidates frequently mark it (and a register) as input. In a control system the actuator acts back on the conditions, so it sits at the output end of the chain, never the input end.
November 2022 (w22): the actuator was the most-missed correct output device and was most often wrongly marked as an input device.
Name the specific device precisely
Name devices specifically. Write "barcode scanner" or "QR code scanner", not just "scanner"; write "USB flash drive", not "USB". Also avoid devices not relevant to the context (e.g. a separate printer or external speaker for a built-in mobile device). A vague or off-context device name is a common, avoidable mark loss.
November 2023 (w23): "scanner" alone was too vague where "barcode scanner" was needed.
Two devices on a line: only first marked
If you write more than one device on a single answer line, only the first is marked. Writing "keyboard / mouse" hoping one is right can score zero if the first is wrong. Commit to a single device per answer line and make sure it is the strongest choice for the context.
November 2022 (w22): where more than one device was written on a single answer line, only the first was marked.
Monitoring watches; control acts
Both systems read sensors, but only one changes conditions. A monitoring system records/displays or alarms and leaves the process unchanged — a human decides what to do. A control system compares the reading with a stored value and signals an actuator that automatically changes conditions (e.g. a thermostat opening a valve).
Five-link sensor→actuator scaffold
For a sensor/microprocessor question, write five steps in context: sensor measures → reading digitised (ADC) → microprocessor compares with a stored value → decides → signals an actuator. Marks live in the compare and actuator steps.
Match the sensor to the quantity word
For "choose the most suitable sensor", underline the quantity word in the stem (acidity, height, brightness) and map it to the sensor that measures it. This blocks the traps — moisture for acidity (needs pH), infra-red for height (needs level).
Name the specific device and context
Name the specific device and tie it to the context: "barcode scanner" (not "scanner"), "USB flash drive" (not "USB"), and a device that fits the scenario. Give a reason linked to the stem, and write only one device per answer line so your best choice is marked.
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