The “Universal Product Code”, also known as UPC Bar Code can be found in almost all packages that you buy from department stores, grocery stores or any other stores.

In this post we will discuss on where these codes come from and their actual use.

Origin of UPC Bar Code

The UPC was first developed by a company called Code Council [UCC] so as to help the small scale department stores and grocery stores to speed up their checking out process and also to make a correct digital track of all the sales that happen in a period of time. The system turned out to be very successful that almost all manufacturers started using this method for all retail products.

The manufacturers have to get a permit from the UCC to use this system. The UCC helps the manufacturer to understand the whole process and gives him a 6 digit manufacturer identification number for an annual fee.

The Coding Process

An item number is assigned for each product and the number is unique until that particular product has stopped its sale in the market. All these unique numbers will be given by a UPC co-ordinator who will be employed by the manufacturer. Take a look at the figure below to know what a UPC bar code looks like.

A UPC code will be a 12 digit number which is divided into two parts.

The machine readable bar code.

The human readable 12 digit UPC number.

Out of the 12 digits the first 6 digits represents the manufacturer’s number and the next five represents the product number. The last number is called the check digit number.

As a result the UPC co-ordinator will have to make different codes for different sized packages of the same product as well. That is 100 gram toothpaste will not have the same barcode as 500 gram toothpaste [both being of the same manufacturer].

As explained earlier, the last digit of a UPC code is the check digit number. The last digit is very important as it allows the scanner to know whether the correct UPC is given for the product. You may be thinking how a single digit helps in verifying the whole number. Actually this single digit is calculated from all the other 11 digits. Take a look at the example given below.

Let the code of a certain product be 63938200039.

Step 1

Take the digits from all the odd positions and add them. That is add the 1^st digit, 3^rd digit, 5^th digit and so on.

6 + 9 + 8 + 0 + 0 + 9 = 32

Step 2

Multiply the answer obtained from step 1 with 3

32 * 3 = 96

Step 3

Take the digits from all the even positions and add them. That is add the 2^nd digit, 4^th digit, 6^th digit and so on.

3 + 3 + 2 + 0 + 3 = 11

Step 4

Add the answer obtained from step 4  to the value in step 2.

96 + 11 = 107

Step 5

This is the last step that determines the check digit.

Determine the smallest number that, when added to the answer in step 4, is a multiple of 10.

107 + 3 = 110

Thus the check digit is 3.

Each time a product is scanned by the scanner, this calculation showed above is performed. The scanner reads a check digit. If the calculated check digit is different from what it reads, then the scanner shows a false signal. Thus the manufacturer will have to recheck the UPC code or has to rescan till it gets the correct code.

Sometimes smaller products are only given smaller digit UPC bar codes called zero-suppressed numbers. Apart from the manufacturers ID, it will be followed by a lot of 0’s.

Product Price Determination

You must have noticed that the price of any product is not given its cover. There will only be a bar code. The idea behind this is that when the customer buys a product, he scans the bar code. Thus the information in the bar code is sent to the store’s central computer to look up the UPC number. The central computer sends back the actual price of the item at that moment.

Due to this method, the manufacturer can easily change the price of the product whenever he wants. This can be a disadvantage as well because the store keeper can easily fool the customer. But the idea was mainly intended to change prices when there is a change in the market price.

The first digit of the manufacturer’s identification number is special. It is called the number system character. The meaning of the different number system in a UPC code is shown below.

0              Standard UPC number (must have a zero to do zero-suppressed numbers)

1              Reserved

2              Random-weight items (fruits, vegetables, meats, etc.)

3              Pharmaceuticals

4              In-store marking for retailers (A store can set up its own codes, but no other store will understand them.)

5              Coupons

6              Standard UPC number

7              Standard UPC number

8              Reserved

9              Reserved

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Electronic Galvanometers

Galvanometer

A vacuum tube or transistor amplifier, followed by a milli-ammeter may be employed as a detector. Some of such devices have arbitrary scale values, sometimes with variable gain, and are designed simply as balance indicators. The sensitivity may be of the order of a microvolt per scale division or better, and the input impedance is in the range of meg ohms, so the current drawn from the measured source is usually negligible. Such instruments have the advantages of ruggedness and portability that permit their use under conditions that would be extremely difficult for a sensitive suspended galvanometer. An­other possibility is a VTVM, if sufficiently low scales are provided. Instruments are avail­able with ranges such as 5-0-5 or 10-0-10 microvolts giving a fraction of a microvolt per scale division, the input impedance is in Mega Ohms. On any of such devices with high input impedance, the indication is practically the Thevenin voltage produced by the unbalance of the bridge or potentiometer, unless the circuit is itself of very high impedance. Elec­tronic detectors are often useful however, there may also be difficulties connected with their use. It is desirable to ground the circuit, if possible, at one of the detector terminals, otherwise stray effects and the capacitance of the body may introduce errors in the meter indications. Also, ac pick-up must be avoided unless the detector internal circuit is immune to it. Another type of electronic detector is shown in figure and essentially consists of a taut-suspension type galvanometer of comparatively low sensitivity, photo electric tubes, an amplifier, and an output meter. The galvanometer used is particularly designed for a low period. The combination gives high sensitivity and fast response.

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Description.
This is perhaps one of the simplest electronic fuse circuit one can make. The circuit uses only one transistor, one SCR, one push button switch and two resistors.
The working of the circuit is very simple. Initially the load current flows through SCR and resistor R1.The value of R1 is so selected that, the maximum load current multiplied by the resistance of R1 is equal to 0.7 volts. When the load current exceeds the maximum value the voltage drop across R1 becomes more than 0.7V and switches transistor Q1 ON. Now the transistor completely bye passes the load current and the current through triac falls below the holding current. This makes the triac OFF. When SCR is OFF there will not be any current flow through R1 and so the voltage across it falls to 0.This makes the transistor OFF, completely isolating the load circuit.The fuse can be resetted by pressing S1.When S1 is pressed the SCR is again triggered and remains latched to conduct the load current.

Circuit diagram.

Notes.

• The circuit can be assembled on a Vero board.
• The value of R1 can be obtained from the equation; [Imax] X [R1] = 0.7V.
• R2 can be obtained from the equation; R2 = [Vs] X [1K Ohms].
• Wattage rating of R1 can be obtained from the equation; W = [Imax] X [Imax] X [R1].
• For this circuit to work the current consumption of the load must be greater than the holding current of the SCR.