CAR PARK BARRIERS,COIN COUNTERS,BAR CODE READER

The system uses a PLC for its operation.There are two barriers used namely in barrier and out barrier. In barrier is used to open when the correct money is inserted while out barrier open when the car is detected in front of it.It shows a schematic arrangement of an automatic car park barrier. It consists of a barrier which is pivoted at one end, two Solenoid valves A and B  and a piston cylinder arrangement.

A connecting rod connects piston and barrier as shown in fig below Solenoid valves are used to control the movement of the piston.Solenoid A is used to move the piston upward inturn barrier whereas solenoid B is used to move the piston downward.

 

Limit switches are used to detect the foremost position  of the barrier. When current flows through solenoid A, the piston in the cylinder moves upward and causes the barrier to rotate about its pivot and raises to let a car through it.

COIN COUNTERS:

Coin counters which accepts mixed denomination of coins.The system should identify the denomination of coins through sensors.The sensor output is to be interfaced to electronic circuitry that should indicate no of coins presented and total value of coins.These two values must be displayed in multiplexed display.

The design is divided into two parts:

 1.Mechanical design

 2.Electronic design

MECHANICAL DESIGN:

It requires a chamber to accept mixed denomination of coins and mechanism to present the coins to sensor array which can read their attributes and output digital signals for computations.A typical horizontal slotted design is shown in fig.Dc motor is used to rotate the disk,as the disk rotate the coin drops into the slot which contains array of sensors.As the size ,weight and thickness of every coin is unique for different coins.This feature of coin is used to determine the value of coins by well designed sensing system.

ELECTRONIC DESIGN:

For determining combination of each different denominations a set of phototransistor - photodiode pairs are used.The signal from these sensors are pulses of different widths with different starting times depending on size and speed of coin.

The sensor output is converted to TTL(Transistor–transistor logic) signals by using schmitt triggers , so the outputs can be compatible to the electronic circuitry.A sequential logic circuit is designed to identify the coin correctly.The Boolean expression   for the different denomination of coins is to be developed.

  e.g

          X= A̅ B̅ C̅

Where 

        A,B,C-corresponds to the sensor output

BAR CODE READER:

The familiar scene at the checkout of a supermarket is of the purchase being passed in front of a light beam or a hand-held wand being passed over the goods so that the bar code can be read and the nature of the purchase and hence its price automatically determined. The code consists of a series of black and white bars of varying widths. For example there is such a bar code on the back of this book. 

Fig shows the basic form of the bar code used in the retail trade. The bar code represents a series of numbers.There is a prefix which identifies the coding scheme being used.This is a single digit for the regular universal product coding scheme used in the US and two digits for the european article number scheme used in europe. The upc uses a 0 prefix for grocery and a 3 for pharmaceuticals. The EAN prefix is from 00 to 09 and is such the UPC code ca be read within the EAN code. This is followed by five digits to represent the manufacturer each manufacturer having been assigned a unique number.This brings up the center of the code pattern which is identified by two taller bar patterns. The five digit number that then follows represents the product.The final number is a check digit which is used to check that the code has been correctly read. A guard pattern of two taller bars at the start and end of the bar pattern is used to frame the bars.

Each number is coded as seven 0 or 1 digits .The codes used on either side of the centre line are different so that the direction of the scan can be determined. To the right the characters have an even number  of 1s and so even parity and for  UPC to the left an odd number of 1s and so odd parity.The EAN coding for the left being a mixture.

Table shows the UPC being the left A coding and the EAN using both left A and left B character codes.

EX: 1101100

Each 1 is entered asa dark bar and thus the right hand character 2 would be represented 1101100 and with the adjacent dark bars run together ,it appears as a double width space. The guard pattern at the ends of the code represents 101 and the central band of bars is 01010.

The bar code shown in the the fig is using the EAN code and has the prefix 97 to identify it as a publication , 80582 to identify the publisher ,25634 to identify the particular book and a check digit of 7. note that the bar code contains the relevant parts of the ISBN number ,this also being a number to identify the publisher and the book concerned .