What goes around comes around

These are a couple of old circular bar codes, dating back to the 1970’s.

The first example was used to track totes filled with tape measures and divert them to the proper gate on a conveyor. The computer system that this symbol was used with was a Computer Identics laser scanner attached to a DEC PDP-8 with Plessey MOS memory and a ‘flip chip’ card decoder on a separate backplane. The scanning software loaded via a paper tape reader.

This is a binary encoded symbol with a value of ‘72’.  The laser scanner only read half of the label, and after it was decoded, the computer diverted the tote to the gate associated with the value 72. This was one of the oldest bar code systems that I have worked with.


The next example is called ‘Split Circle Code’. It was developed in  1974 by Bendix Recognition Systems.

The circle was split in half, with each half encoding part of the symbol.  This type of symbol required that both halves of the circle be read, so there were orientation issues that had to be dealt with in order to get good reads.

Bendix encoded these symbols as BCD (binary coded decimal) values and they were printed by Bendix printers.

This example was used in a baggage handling system at Eastern Airlines which used a Bendix scanner to read the labels at a rate of 70 bags per minute.

You can still see the texture of the luggage that the label was applied to.

Apparently, many customers had complaints about the adhesive residue left behind when the label was removed and this ultimately led to the demise of these scanning systems.

Will RFID make all of my dreams come true?

People unfamiliar with RFID technology expect to walk into a room, turn on an RFID reader and read all of the tag inside of the room. It doesn’t work that way.

RFID is a great data collection tool but you should be familiar with its basic operation. Our industry mostly uses passive UHF tags that operate in the 900 MHz frequency. Here’s a typical RFID inlay, or circuit:

The little black dot in the middle of the inlay is the RFID chip, the rest is the antenna. This is a passive tag which means that it does not use a battery, the tag gathers energy from radio waves aimed at it. Electromagnetic waves are made up of two waves, one electrical and one magnetic. When the magnetic part of the wave cuts across the antenna an electrical current is induced, which charges up the RFID chip. When enough energy is stored the RFID chip can begin to communicate. It does this by powering the antenna on and off, which reflects the incoming radio wave (on) or lets it pass through (off). Rapidly turning the antenna on and off is how the RFID chip modulates the reflected signal, which is how data is sent back to an RFID reader.

So there’s a couple of important things to note from this. First, the RFID inlay does not transmit radio signals, it reflects them, so the power coming back to the reader is quite small. People think that RFID tags work like the transponders in their cars that are used to collect toll information. These are active tags that have in internal battery and really do create and transmit radio waves (transmitter/responder) and have much greater range than passive RFID.

Secondly, the RFID circuit gathers energy from the magnetic part of the radio wave aimed at it, and sometimes the tag’s antenna can be orientated to that this doesn’t happen and the tag can’t be read. Radio waves can be blocked, absorbed, or reflected, by nearby materials, preventing the tag from being powered up or read. There are a lot of things that can go wrong.

RFID is a great technology, but it should be approached with caution. Always test your RFID tags in the environment where they will be used with the readers and antennas that you have chosen to make sure your application will be robust and reliable.


How does UPC work?

Here’s a typical UPC symbol from a box of Hefty trash bags:

UPCA symbol
UPC-A symbol

You can see that UPC is made up of 12 numbers. We’ll ignore the first and last numbers for now and just pay attention to the middle 10 digits.

The first five digits are assigned to one manufacturer. These manufacturer numbers are centrally managed, assigned, and sold by Global Standard One, or GS1, a non-profit organization. GS1 was formerly known as the UPC Code council.

Once a company is assigned a UPC code it’s up to them to assign the last five digits to their products as they choose. The company then informs GS1 of these product code assignment and GS1 adds them to its master database  which is made available to third parties, like your local grocery chain to do look ups at their cash registers.

A UPC code is really a pointer to a record in the GS1 data base. The description and price are returned from the database lookup.

One interesting thing about UPC is that there are two different symbol patterns that encode each number depending on if it’s on the left or right side of the symbol. Look at how the number three is encoded differently on the two sides of this symbol:

This was done to allow omni-directional scanning with early supermarket scanners. These were often just a couple of laser lines that intersected at 90 degrees, like a plus (+) sign. Because the numbers were encoded differently on the left and right it allowed scanners to read the symbol a half at a time and put it together before transmitting. Each half of the symbol is taller than it is wide (oversquare) so it’s guaranteed to completely pass through one of the laser lines in a single pass.