Computer Hardware and Logic Circuits: Question 8

Worked solution

Part (a): Converting the sensor’s analogue signal

Physical quantities such as temperature vary continuously, so a temperature sensor produces an analogue signal. A processor can only store and process digital (binary) data, so this signal must first be converted. The component that performs this conversion is an analogue-to-digital converter, abbreviated ADC. [2 marks]: [1] for naming the correct component (analogue-to-digital converter), [1] for the correct abbreviation, ADC.

Part (b): The steps of one control cycle

Working through the system in the order the description gives:

1. The temperature sensor takes a reading of the current air temperature inside the greenhouse, producing an analogue signal.
2. The ADC converts this analogue reading into digital data that the processor can work with.
3. The processor compares the digital temperature reading against the target temperature value already stored in the system’s memory.
4. Based on this comparison, the processor makes a decision: if the reading is below the target, it sends a signal that switches the heater on; if the reading has reached or exceeds the target, it sends a signal that keeps (or switches) the heater off.

[4 marks]: [1] mark for each of the four steps above, in a logically correct order (take reading; convert with ADC; compare with stored target; decide and act on the heater).

Part (c): Why this is a feedback system

The heater’s action (switching on) changes the very quantity the sensor is measuring: it raises the air temperature in the greenhouse. That new, changed temperature is then picked up by the sensor as its next reading, which is fed back into the same comparison-and-decision process described in part (b).

Because each cycle’s output (the temperature change the system itself caused) becomes the input to the next cycle, the system is continuously adjusting its own behaviour in response to the results of its own previous actions. This looping relationship between output and input is what is meant by feedback. [2 marks]: [1] for identifying that the heater’s effect on temperature becomes the sensor’s next reading, [1] for explaining that this creates a continuous loop where the system’s own output affects its own future input/behaviour.

Part (d): Classifying the heater

The heater is an output device. [1 mark] It does not sense or supply any data about the environment to the processor; instead, it receives a control signal from the processor and converts that signal into a physical effect (heat) in the greenhouse. Producing a physical effect from a processor’s signal, rather than supplying data to the processor, is the defining role of an output device (here, more specifically, an actuator).

Final answers

• (a) Analogue-to-digital converter (ADC).
• (b) Sensor takes a reading; ADC converts it to digital; processor compares it with the stored target temperature; processor switches the heater on (if below target) or off (if at/above target).
• (c) The heater’s effect changes the temperature the sensor next measures, so the system’s own output becomes its next input, forming a continuous feedback loop.
• (d) Output device. It receives a control signal and produces a physical effect (heat) rather than sensing or supplying data.