Design and Applied Technology | Systems and control

Design and Applied Technology: Systems and Control

Hey everyone! Welcome to your study notes for Systems and Control. Don't worry if this topic sounds a bit technical. We're going to break it down into simple, easy-to-understand parts. Think of it like learning the secret rules of how everyday gadgets work, from your phone to a washing machine. Understanding systems is a superpower for any designer or engineer, and by the end of this, you'll be able to see the world in a whole new, systematic way!

The Basic Building Block: Input-Process-Output (I-P-O)

Almost everything that is designed to perform a task can be understood as a simple system. The most basic way to think about this is using the Input-Process-Output (I-P-O) model. It's a simple three-step flow that describes how a system works.

Let's use an everyday analogy: Making toast!

• Input: You put a slice of bread into the toaster and push the lever down. The inputs are the bread, electricity, and your action of pushing the lever.
• Process: The toaster's internal heating elements get hot and toast the bread for a set amount of time. This is the "action" or "thinking" part.
• Output: The finished toast pops up! The output is the toasted bread and heat.

Here’s the official breakdown:

• Input: The energy, material, or information that the system needs to start working. It's the "what you put in".
• Process: The action or change that the system performs on the input. It's the "what it does".
• Output: The result or product that comes out of the system after the process is complete. It's the "what you get out".

We can draw this as a simple block diagram:
[ INPUT ] ---> [ PROCESS ] ---> [ OUTPUT ]

Real-World Examples from the Syllabus

1. A Hair Dryer

• Input: Electricity from the wall socket, pressing the 'on' switch.
• Process: An electric motor spins a fan, and a heating coil gets hot.
• Output: A stream of hot air.

2. A Washing Machine

• Input: Dirty clothes, water, detergent, electricity, pressing the 'start' button.
• Process: The machine fills with water, the drum rotates to wash the clothes, the dirty water is drained, and the drum spins fast to remove excess water.
• Output: Clean, damp clothes.

What about Complex Systems? Sub-systems!

Very complex products are made of many smaller systems working together. We call these sub-systems. Think of a car. The whole car is the main system, but the engine is a sub-system, the braking is a sub-system, and the air conditioning is another sub-system. They all have their own I-P-O but work together to make the car run.

For example, the MTR system is a huge system. It includes mechanical sub-systems (the trains and rails), electronic sub-systems (the Octopus card readers and signals), and even pneumatic sub-systems (the air-powered doors).

Key Takeaway for I-P-O

The Input-Process-Output model is a fundamental tool to analyse and understand how any product or system works. If you can identify the I-P-O of a device, you're already thinking like a designer!

Making Decisions: Logic Gates

How does an electronic system "decide" what to do? The answer lies in logic gates. These are the simplest decision-makers in electronics. They work with binary signals: 1 (ON or TRUE) and 0 (OFF or FALSE).

A logic gate takes one or more binary inputs and produces a single binary output based on a simple rule. For the DSE, you need to know three basic ones: AND, OR, and NOT.

The AND Gate

Rule: The output is 1 only if ALL inputs are 1.

Analogy: Think of a microwave oven. For it to start (Output=1), the door must be closed (Input A=1) AND you must press the start button (Input B=1). If either one is not done, the microwave won't start.

Truth Table: (A table showing all possible input combinations and the resulting output)

Input A     Input B     Output
    0             0               0
    0             1               0
    1             0               0
    1             1               1

The OR Gate

Rule: The output is 1 if AT LEAST ONE input is 1.

Analogy: Think of a doorbell in a flat with two doors. The bell will ring (Output=1) if someone presses the button at the front door (Input A=1) OR the button at the back door (Input B=1). It doesn't matter which one, as long as one is pressed.

Truth Table:

Input A     Input B     Output
    0             0               0
    0             1               1
    1             0               1
    1             1               1

The NOT Gate (or Inverter)

Rule: The output is the OPPOSITE of the single input.

Analogy: Think of an emergency light that turns on automatically when the power fails. When there is mains power (Input=1), the light is OFF (Output=0). When the power fails (Input=0), the light turns ON (Output=1).

Truth Table:

Input     Output
    0             1
    1             0

Key Takeaway for Logic Gates

Logic gates are the fundamental building blocks of all digital electronics. AND, OR, and NOT gates make simple logical decisions that, when combined, can perform incredibly complex tasks.

Getting Things Moving: Mechanical Systems

Mechanical systems use forces and movement to accomplish a task. They are all about gears, levers, and linkages. In DAT, we often think about them in the context of changing one type of motion into another, for example, when designing a mechanical toy.

Common Motion Conversion Mechanisms

• Linkage: A system of connected rods that can be used to transfer or change the direction of motion. Example: The mechanism that makes a rubbish bin lid open when you step on the pedal.


• Cam and Follower: A specially shaped rotating piece (the cam) pushes another part (the follower) up and down or back and forth. This creates a repeating, specific pattern of movement. Example: In an automaton toy, a cam can make a character's arm wave as a handle is turned.


• Slider-Crank: This mechanism converts rotary motion (spinning) into reciprocating motion (back and forth in a straight line), or vice versa. Example: The piston and crankshaft in a car engine, or the wheels and coupling rods of an old steam train.


• Rack and Pinion: A circular gear (the pinion) meshes with a flat, toothed bar (the rack). When the pinion rotates, the rack moves in a straight line. Example: The steering system in most cars. Turning the steering wheel (pinion) moves the rack to turn the car's wheels.


• Ratchet and Pawl: A useful device that allows motion in only one direction and prevents it from moving backward. Example: A zip tie – you can pull it tighter, but you can't loosen it. Another example is a socket wrench that clicks when you turn it one way but grips when you turn it the other.

Key Takeaway for Mechanical Systems

These simple mechanisms are the building blocks for almost all machines. By understanding how to convert motion, you can design products that move in interesting and useful ways.

Staying Strong: Physical Structure

A product isn't just about what it does; it's also about how it holds together under different forces. This section is about making sure our designs are strong and stable.

Forces and Strength

Structures must be able to withstand forces (pushes and pulls). A strong design distributes these forces so that no single part is overloaded. Using shapes like triangles in a framework (called a truss) is a classic way to create very strong, yet lightweight, structures. Think of bridges or crane arms!

Stability and Balance

Stability is a structure's ability to resist being knocked over. This is mainly determined by two things:

1. Centre of Gravity (CG): The imaginary "balance point" of an object. The lower the centre of gravity, the more stable the object.
2. Base of Support: The area of the object that is in contact with the ground. The wider the base of support, the more stable the object.

Analogy: Imagine a pyramid and a tall, thin drinking glass. The pyramid has a very wide base and a very low CG, making it incredibly stable. The glass has a narrow base and a higher CG, making it easy to knock over. When designing a product like a table lamp or a floor fan, you should always aim for a wide, heavy base to keep it stable.

Key Takeaway for Physical Structure

Good design isn't just functional; it's also structurally sound. Always consider the forces a product will face and design for stability by using a wide base and a low centre of gravity.

The Power of Electrons: Basic Electronics

This is where we bring everything together! Basic electronic systems use the I-P-O model we learned earlier. You'll often build simple circuits like these using electronic learning kits.

A simple electronic control circuit has three main parts:

• Input (Sensors): These components "sense" the world around them. Examples: A Light Dependent Resistor (LDR) detects light levels, a thermistor detects temperature, and a push-button switch detects a press.


• Process (Control): This is the "brain" of the circuit that makes a decision. It could be a simple circuit with a few transistors or logic gates, or a more complex micro-controller. This part decides what to do based on the information from the sensor.


• Output (Actuators): These components "do" something. They create an effect like light, sound, or movement. Examples: A Light Emitting Diode (LED) lights up, a buzzer makes a noise, or a motor spins.

A Simple Example: Automatic Night Light

Let's design a simple automatic night light using our I-P-O and electronics knowledge.

• Input: An LDR (Light Dependent Resistor) to detect when it gets dark.
• Process: A simple processing circuit (perhaps using a NOT gate logic!) that says: "IF the LDR detects darkness, THEN send a signal to turn on the light".
• Output: An LED (Light Emitting Diode) that turns on and produces light.

Working with electronic learning kits is the best way to see these principles in action. It's really satisfying to build a circuit that responds to its environment!

Key Takeaway for Basic Electronics

Simple electronic systems follow the Input-Process-Output model, using sensors to gather information, a processing circuit to make a decision, and an actuator to produce an output.