AUTOMATA PRESENTATION

Topic: Working of a Turnstile

PRESENTED BY:

Rishabh Srivastava

Mudit Mishra

CONSTRUCTION OF A TURNSTILE USING

FINITE AUTOMATA

TURNSTILE (An Overview)

A turnstile is a mechanism that allows a location to have control over entry and

exit. It used to control access to subways and amusement park rides, is a gate

with three rotating arms at waist height, one across the entryway. Initially the

arms are locked, barring the entry, preventing customers from passing through.

Depositing a coin or token in a slot on the turnstile unlocks the arms, allowing

them to rotate by one-third of a complete turn, allowing a single customer to

push through. After the customer passes through, the arms are locked again until

another coin is inserted. Given below is a figure of a turnstile.

Fig 1: Turnstile

Turnstile is a simple mechanism modeled on FINITE-STATE AUTOMATON.

FINITE STATE AUTOMATON

Finite-State Automaton (plural: automata), or simply a state machine, is a

mathematical model of computation used to design both computer

programs and sequential logic circuits.

The machine is in only one state at a time; the state it is in at any given time

is called the current state.

It can change from one state to another when initiated by a triggering

event or condition; this is called a transition.

The behavior of state machines can be observed in many devices in modern

society which perform a predetermined sequence of actions depending on

a sequence of events with which they are presented. Simple examples are

vending machines which dispense products when the proper combination

of coins are deposited, elevators which drop riders off at upper floors

before going down, traffic lights which change sequence when cars are

waiting, and combination locks which require the input of combination

numbers in the proper order.

The finite state machine is weak; it has less computational power than

some other models of computation such as the Turing machine. This is

because the FSM has limited memory.

CONSTRUCTION OF A TURNSTILE USING FINITE

AUTOMATON

The turnstile has two states: Locked and Unlocked.

There are two inputs that affect its state: putting a coin in the slot (coin)

and pushing the arm (push).

In the locked state, pushing on the arm has no effect; no matter how many

times the input push is given it stays in the locked state.

Putting a coin in, that is giving the machine a coin input, shifts the state

from Locked to Unlocked.

In the unlocked state, putting additional coins in has no effect; that is,

giving additional coin inputs does not change the state.

However, a customer pushing through the arms, giving a push input, shifts

the state back to Locked.

Given below is a state diagram for a TURNSTILE:

Fig 2: State Diagram of a Turnstile

KEYWORDS USED:

STATE: A state is a description of the status of a system that is waiting to execute

a transition.

TRANSITION: A transition is a set of actions to be executed when a condition is

fulfilled or when an event is received.

SEQUENTIAL CIRCUITS: A sequential circuit is one in which the present output is

dependent upon the present input and past output. So we need a memory unit to

store the past output.

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BIBLIOGRAPHY

www.wikipedia.org

Finite State Automata at the Open Directory Project.

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