Bar code Reader. How Stuff Works

Barcode is a label with white and black stripes to denote the specification of a product. It is generally used to represent the products features, prize, quantity etc in coded form. This is meant to avoid malpractices during billing and sale. To retrieve the data from the bar code label, a barcode reader is used which is now common in commercial establishments like Super markets. The barcode reader is an electronic device connected to a computer. Its face has a light source either Laser or Infrared. The light reflects back from the barcode and the Photodiode in the reader translates the optical impulses into the corresponding electric signals. The barcode reader also has a Decoder to analyze the barcode’s image data from the sensor and to transfer it into the computer.

How it works?

The barcode reader has a light source like Laser and a Photodiode on the head. The light source emits light which reflects back from the space between the bar codes. The Photodiode measures the intensity of the reflected back light when the head crosses each bar and the space between the bars. As a result, the Photodiode generates a waveform corresponding to the width of the bars and spaces in the label. When the light passes across the barcode label, the dark bands absorb light while the white spaces reflect light. So the voltage waveform generating will be similar to the bar and space patterns. The decoder translates the waveform into corresponding data.
Based on the technology, the barcode readers are classified into

1. Pen type reader

It is just like a pen with a light source and a Photodiode the tip. The barcode reading occurs when the tip of the pen reader is moved across the barcode label with uniform speed just like a scanning.

2. Laser reader

The working of laser reader is similar to pen reader but it uses laser as the source of light. A prism arrangement is present in the laser reader to scan the laser beam back and forth across the bar code. A photodiode detects the reflected back laser light intensities. The light emitted by the reader is rapidly varied in brightness with a data pattern, so that the receiver circuitry is designed to detect only signals with the same modulated pattern.

3. CCD Reader

In CCD reader, an array of numerous light sensors is used in the head of the reader. Since the light sensors are arranged in rows, the voltage pattern that develops in the reader will be identical to the pattern generated by the barcode. CCD reader measures the emitted ambient light from the bar code and not the reflected light as in the case of Laser and Pen readers.

4. Video camera reader

It uses small video camera to scan the bar code back and forth. It is the newest type using the CCD technology. The light sensors are arranged in a two dimensional array so that it can generate an image easily.

Based on the housing, the bar code readers are classified into

1. Stationary reader – It is a table top type in which the barcode label is passed in front of its head.

2. Handheld reader – Having a handle and a button to trigger the light source

3. Wand scanner – It is the pen scanner with a probe to scan the bar code.