Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

This page supports the lesson note with a companion video and a short classroom-ready summary.

For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.

Performance objectives

• Define a system and its components with South African examples.
• Explain and differentiate between open-loop and closed-loop control systems.
• Describe the concept of processing in technological systems.
• Identify processing devices like microcontrollers.
• Design a simple system to solve a community problem.

Lesson summary

This week, we will be revising and consolidating key concepts covered in Grade 7 Technology so far. Technology plays a vital role in our lives, from the cellphones we use to communicate to the infrastructure that provides us with electricity and clean water. Understanding these principles helps us to be informed citizens, innovative problem-solvers, and potential future inventors who can contribute to South Africa's development. By revisiting these topics, you'll strengthen your foundation for future technology studies. This week's focus is on Systems and Control, and Processing.

Lesson notes

2. 1. Systems A system is a set of interacting or interdependent components forming a complex whole. Systems are all around us, from the water cycle to a simple bicycle. They take inputs, process them, and produce outputs. Crucially, they often involve feedback.

Input: The resources or signals that enter the system.

Examples: electricity, water, raw materials.

Process: The action or series of actions that transform the input.

Examples: refining oil, cooking food, manufacturing a product.

Output: The result of the process.

Examples: petrol, a cooked meal, a manufactured car.

Feedback: Information about the output that is sent back to the input to adjust the process. This helps to maintain desired results and stability.

Example: A thermostat sensing room temperature and adjusting the heater accordingly. South African

Example: Consider a community water purification system.

Input: Raw water from a river or dam.

Process: Filtration, chemical treatment, and disinfection.

Output: Clean, potable water.

Feedback: Regular water quality testing ensures the output meets health standards, adjusting the treatment process if necessary. 2.

2. Control Systems A control system regulates the behaviour of a system.

There are two main types: Open-loop control system: The output has no influence on the control action. The system runs based on pre-set parameters without feedback.

Example: A toaster. You set the timer (input), and the toaster heats the bread for that amount of time (process), resulting in toasted bread (output). There's no sensor to check if the bread is actually toasted to your liking; the process runs regardless.

Closed-loop control system: The output is measured and fed back into the system to adjust the control action. This creates a feedback loop, allowing the system to respond to changes and maintain a desired state.

Example: A geyser with a thermostat. The thermostat measures the water temperature (feedback). If the water is below the set temperature, the heating element turns on (process). Once the water reaches the desired temperature (output), the thermostat turns off the heating element. 2.

3. Processing Processing refers to the transformation of inputs into outputs within a system. It involves the application of energy, information, or materials to alter the state or characteristics of the input. Processing occurs through various mechanisms, including mechanical, electrical, chemical, and computational processes. In technological systems, processing often involves a central processing unit (CPU), microcontroller, or other device that executes instructions to manipulate data or control physical processes.

Example 1: In a car, the engine processes the fuel (input) and air to create motion (output).

Example 2: In a computer, the CPU processes data (input) to display information on the screen (output). 2.

4. Processing Devices: Microcontrollers A microcontroller is a small, integrated circuit that contains a processor core, memory, and programmable input/output peripherals. They are commonly used to control electronic devices, such as washing machines, traffic lights, and industrial equipment.

How they work: Microcontrollers are programmed with instructions that tell them how to respond to inputs and control outputs. They can read data from sensors, perform calculations, and activate actuators to achieve a desired result.

Example: In a solar-powered water heater, a microcontroller can monitor the water temperature and solar panel output. When the solar panel is generating sufficient energy, the microcontroller can activate a pump to circulate water from the storage tank to the solar panel for heating. If the water temperature reaches the set point, the microcontroller deactivates the pump to prevent overheating. Guided Practice (With Solutions)

Question 1: Identify the input, process, and output in a maize grinding mill.

Solution: Input: Maize kernels Process: Grinding the maize kernels using mechanical force.

Output: Maize meal (mealie meal)

Commentary: This question helps students identify the basic components of a system within a familiar South African context.

Question 2: Is a security gate that automatically closes after a certain time an open-loop or closed-loop system? Explain your answer.

Solution: This is an open-loop system. The gate closes after a pre-set time, regardless of whether someone is still passing through. There's no feedback mechanism to sense if the gate needs to stay open longer.

Commentary: This question tests understanding of the difference between open- and closed-loop control. The example is relevant to South African learners' daily lives, given the prevalence of security gates.

Question 3: Describe how a closed-loop control system could be used to regulate the temperature in a greenhouse.

Solution: A temperature sensor inside the greenhouse measures the air temperature (feedback). The sensor sends the temperature reading to a controller (e.g., a microcontroller).