Chapter 4 - Control circuits

What is a microcontroller?

A programmable integrated circuit that can be loaded with software to carry out different tasks

Give examples of devices that use microcontrollers.

Microwave ovens, washing machines, refrigerators, cameras, cars, toys, security systems

What are the key parts inside a microcontroller?

Program memory, data memory, bidirectional input/output ports, clock oscillator—all in one IC

What are two types of control systems (besides microcontrollers)?

On-off control (e.g. thermostats), sequential control (e.g. traffic lights with timers and logic)

What is meant by 'hardwired' when talking about control systems?

System’s function is determined by fixed connections and components, can only change by rewiring

What is the advantage of a microcontroller-based control system?

Can be reprogrammed for different tasks, more flexible, more compact than hardwired equivalents

What is the main disadvantage of using a microcontroller?

Generally more expensive IC, requires computer + programming software

How do you program a microcontroller?

Write program (usually using flowcharts or a high-level language) on computer, convert to machine code, download via cable to microcontroller

Will a microcontroller keep its program if turned off?

Yes, it has program memory that stores code even without power

What does 'interfacing' mean in digital control?

Connecting input circuits (sensors) and output devices (e.g. LEDs, motors) to the microcontroller’s pins

Can you connect an LED directly to a microcontroller output?

Yes, but high-power outputs (motors, relays) need a transistor or MOSFET interface

What is a flowchart in control programming?

A diagram using boxes/arrows to show sequence of commands and program logic

Name three common types of flowchart boxes.

Start/Stop; Process (calculation/delay); Decision; Output/Input

What does a Decision box in a flowchart represent?

A yes/no question; program branches depending on the answer

What are common operations you can do in flowchart control?

Input, Output, Counting, Branching (decision), Testing, Time delay, Arithmetic

Give an example of a simple microcontroller program task.

Blink an LED for 5s, then turn off for 2s, then blink with a different color for 3s

How do you make a flowchart repeat (loop continuously)?

Draw an arrow from end of process sequence back to the start

What are the standard software operations for a timed sequence?

Output on/off, wait/delay for time, loop or branch

What is positional control using a servo motor?

Turning a motor shaft to a precise angle using pulses from microcontroller

How does a microcontroller control a servo’s shaft position?

Sends timed pulses; shaft angle depends on pulse width (e.g. 1.5ms pulse gives 90°)

Example: What output value moves a servo to 0°, 90°, 180°?

0° = 75; 90° = 150; 180° = 225 (using position = angle/1.2 + 75)

Why are microcontrollers used in cars?

Control of engine, brakes, lighting, wipers, comfort and safety systems—flexible and compact

What type of control is used in a room heater?

On-off control: heater turns on/off depending on sensed temperature

How is a traffic light sequence typically created?

Sequential timer/counter, logic for each state, outputs for lights, or software in a microcontroller

Why is flowchart programming useful?

Makes program logic clear, avoids syntax errors, can simulate/test before loading to chip

What do ‘input’ and ‘output’ mean in microcontroller flowcharts?

Input: checks sensor/button; Output: sends digital signal to a device (LED, relay)

What does a 'wait' (delay) box do in a flowchart?

Halts program for given time before next step

How can a program test the status of a digital input?

Use a decision ("Is input X on?") box that takes Yes or No path

How can you make a light flash until a stop switch is pressed?

Loop through 'on', wait, 'off', wait, check if stop switch is pressed, if no, repeat

How can an input be tested repeatedly until it is true?

Loop arrow back to decision box if answer is 'No' (polling)

Give an example where branching occurs after a decision.

If switch pressed, turn on light; if not, turn on buzzer (2 outputs, single test)

What is an analogue input in a microcontroller?

A pin that reads a range of voltages (not just on/off)

How can a flowchart use an analogue sensor for control?

Decision box checks if sensor value above/below threshold, then acts accordingly

Give a practical example of an analogue input decision.

If temp > 35°C, turn on fan; else, fan off

How can a microcontroller be used as a counter?

Software stores a variable for count, increments it with each event, triggers output after set value

What is a real-life example of using a counter in a control system?

Counting passengers into a lift, packing items in a box, counting cars in a car park

How do you create a loop that counts to a number in flowchart?

Set counter to 0, increment by 1 every event, test for value, repeat until reached

How does a microcontroller know which input/output pin is connected to each device?

User specifies pin assignments in program/code, based on the wiring/board schematic

Why are flowchart-based programs easier for beginners?

Visual, easier to debug/test, avoids complicated syntax, can see program structure clearly

Can microcontrollers handle both digital and analogue signals?

Yes, most have dual-purpose pins (check data sheet)

How do inputs (buttons, switches, sensors) connect to flowchart programs?

Defined as inputs in code; decisions/test steps evaluate their state

How does a counter variable work in control logic?

Stores a number, increments/decrements, used for comparisons/branching in flowchart

What is a servo motor used for in a microcontroller project?

Controlling position of levers, signals, robotic arms, model vehicle steering

How would you drive a high-power output from a microcontroller?

Use transistor/MOSFET interface circuit (microcontroller drives base/gate, output device powered via transistor)

What kind of signal is needed to drive a servo motor?

Pulse of variable width (PWM); position determined by duration of pulse

Name a simple at-home use for a microcontroller and flowchart control.

Automatic pet feeder, garden watering system, nightlight, digital timer

Why are microcontrollers increasingly used in vehicles and appliances?

More features, customization by software, smaller/cheaper than logic gates/counters, easy firmware updates

What makes a microcontroller-based control system “flexible”?

Can reprogram for a new use with software, no rewiring needed

What devices might you control with a microcontroller in a project?

LEDs, buzzers, relays, motors, displays, sensors