Question

Draw state machine models of the control software for the following systems: An automatic washing machine that has different programs for different types of clothes. The software for a compact disk player. A telephone answering machine that records incoming messages and displays the number of accepted messages on an LED display. The system should allow the telephone owner to dial in, type a sequence of numbers (identified as tones) and have the recorded messages replayed over the phone. A vending machine that can dispense coffee with and without milk and sugar. The user deposits a coin and makes his or her selection by pressing a button on the machine. This causes a cup with powdered coffee to be output. The user places this cup under a tap, presses another button and hot water is dispensed.

Short answer

State machines for each system involve identifying key operations and transitions, such as from off to running states and processing user inputs.

Step-by-step solution

Identify the Components of the Automatic Washing Machine

To develop a state machine model for the automatic washing machine, begin by identifying the distinct states through which the machine can transition. These states include: Off, Select Program, Fill Water, Wash, Rinse, Spin, and Complete. Each program chosen for a different type of clothes determines different paths through these states.

Develop the State Machine for the Washing Machine

Create a state diagram where transitions occur based on user inputs and program instructions. For example, from the Off state, pressing the start button transitions to the Select Program state. Choosing a program advances to Fill Water, then Wash, etc., until all processes are complete.

Identify Components of a Compact Disk Player

Identify the key components and interactions a compact disk player experiences. Common states include Off, Load Disk, Play, Pause, Stop, Eject, and Error State (if the disk is unreadable or missing).

Create the State Machine for the Compact Disk Player

Design a state machine that allows transitions between states according to user actions such as pressing play/pause, stop, or eject. Begin at Off. Loading a disk moves to Load Disk, pressing play advances to Play, etc.

Define States for Telephone Answering Machine

Determine necessary states for the telephone answering machine, such as Idle, Recording, Playing Messages, and Counting Messages. Other important states include Message Stored, Number Displayed, Message Replay, and Remote Access.

Build the State Machine for the Answering Machine

Develop a state machine where the machine transitions according to events like incoming calls, message recording, and playback commands. E.g., Idle becomes Recording upon receiving a call; recording completes, transitioning to Message Stored.

Define the Vending Machine States

Recognize the core states for the vending machine: Idle, Coin Inserted, Selection Made, Dispense Cup, Add Ingredients, Dispense Water, and Return to Idle.

Design the Vending Machine State Machine

Design a state diagram beginning at Idle, transitioning to Coin Inserted when a coin is deposited. Subsequent inputs (e.g., button presses for milk/sugar) lead through Dispense Cup, Add Ingredients, and Dispense Water, before returning to Idle.

Key concepts

Automatic Washing Machine

An automatic washing machine is a marvel of modern technology, offering various programs tailored to different types of clothing. To understand how it functions in terms of state machine models, we need to consider its distinct operational states:

• Off: The machine is powered down and inactive.
• Select Program: This state allows users to choose an appropriate washing cycle suitable for their laundry.
• Fill Water: Once the program is set, water fills the drum to a suitable level.
• Wash: The washing process begins, cleaning the clothes as per the chosen program.
• Rinse: Detergent residues are removed by rinsing the clothes with clean water.
• Spin: Excess water is extracted from the clothes through spinning.
• Complete: The washing cycle ends, and the clothes are ready to be removed.

These states can transition from one to another based on user inputs, such as pressing a start button, and the internal logic determined by the selected program. This process ensures that each clothing type is treated optimally, demonstrating the use of state machine models in everyday appliances.

Compact Disk Player

The compact disk player, once a staple in music listening, operates through a series of defined states. Understanding these states helps us grasp how such a player functions internally:

• Off: The player is not active, conserving power.
• Load Disk: Inserting a compact disc triggers this state, preparing the player to read the disk.
• Play: Playback of audio content begins, prompted by pressing the play button.
• Pause: Music is temporarily stopped; the disk continues spinning but does not play audio.
• Stop: Ending playback completely, the disk ceases all motion, and audio output stops.
• Eject: The disk is ejected from the player, allowing for removal or replacement.
• Error State: This state is activated if there is an issue, such as a disk read error.

State machines for CD players ensure seamless transitions between actions based on user inputs, providing a smooth audio experience.

Telephone Answering Machine

The telephone answering machine, a pivotal device in telecommunication, efficiently handles calls and messages through well-defined states. Here's how it operates:

• Idle: The default waiting state, ready to receive incoming calls.
• Recording: Engaged once a call is received; the machine records the caller's message.
• Playing Messages: Allows playback of stored messages, which can be accessed anytime.
• Counting Messages: Tracks the number of messages, often displayed on an LED screen.
• Message Stored: Confirms a message has been saved successfully.
• Number Displayed: Shows the number of messages on an LED display.
• Message Replay: Replays recorded messages over the phone, useful for remote message checks.
• Remote Access: Permits the owner to access messages remotely, ensuring flexibility.

By transitioning between these states based on call activity and user commands, the answering machine manages voicemail effectively, enhancing communication efficiency.

Vending Machine Software

Vending machines, ubiquitous in public spaces, rely on software that guides them through a sequence of states to dispense items effectively. Here's how the state machine model applies:

• Idle: The machine is on standby, waiting for user interaction.
• Coin Inserted: Accepts currency, initiating the transaction process.
• Selection Made: Users select a product by pressing buttons, deciding the outcome.
• Dispense Cup: A cup is delivered for the user to collect, often beneath a dispensing area.
• Add Ingredients: For options like coffee, this state may involve adding milk or sugar.
• Dispense Water: Hot water fills the cup, completing the drink preparation.
• Return to Idle: Completes the process, resetting for the next user.

This efficient sequence ensures that users receive the correct product selection quickly and accurately. Vending machine software exemplifies how state machines enhance user interaction and transaction reliability.