An automated greenhouse uses sensors and a microprocessor to control growing conditions. (a) State the purpose of the ADC (Analogue-to-Digital Converter) in...

(a) Purpose of the ADC (Analogue-to-Digital Converter): [2]

The ADC converts the analogue (continuous) signals produced by the temperature and humidity sensors into digital signals that the microprocessor can process. [1] Sensors produce varying voltage levels that change smoothly and continuously, but the microprocessor can only work with discrete binary values (0s and 1s). [1]

(b) Why an ADC is needed: [2]

Sensors produce analogue data: continuous electrical signals whose voltage varies smoothly with the physical quantity being measured (temperature, humidity). [1] The microprocessor is a digital device that processes data as binary numbers. Without the ADC to bridge between the analogue sensor world and the digital processing world, the microprocessor would be unable to interpret the sensor readings. [1]

(c) Role of the microprocessor: [2]

The microprocessor receives digital data from the sensors (via the ADC) and compares the readings against pre-programmed threshold values stored in its memory. [1] Based on the comparison results, it sends control signals to the actuators (heater and water spray) to maintain the desired growing conditions. For example, if the temperature is below the threshold, it activates the heater. [1]

(d) What an actuator is: [1]

An actuator is a device that receives a control signal from the microprocessor and performs a physical action in response. Examples include motors, valves, heaters, and pumps. In this system, the heater converts electrical energy to heat, and the water spray mechanism opens a valve to release water.

(e) System response when temperature falls below the threshold: [3]

The temperature sensor continuously takes readings of the greenhouse temperature, and the ADC converts these analogue readings to digital values. [1] When the digital reading falls below the set threshold (e.g. 18 degrees), the microprocessor sends a signal to turn on the heater. [1] The sensor continues monitoring the temperature. As the heater warms the greenhouse, the temperature rises. When it reaches or exceeds the threshold, the microprocessor sends a signal to turn the heater off. This continuous cycle of monitoring, comparing, and adjusting is a feedback loop. [1]

(f) Two differences between RAM and ROM: [1]

• RAM is volatile (loses contents when power is turned off) while ROM is non-volatile (retains contents without power)
• RAM can be read from and written to during normal operation, while ROM can only be read from (contents are fixed during manufacture or by special programming)