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

1. AUTOMATA PRESENTATION
Topic: Working of a Turnstile
PRESENTED BY:
Rishabh Srivastava
Mudit Mishra

2. 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

3. 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.

4. 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

5. 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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6. BIBLIOGRAPHY
 www.wikipedia.org
 Finite State Automata at the Open Directory Project.
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