How do supermarket cash registers scan barcodes? Have you ever understood this? Let's take a look at it and hope to help you.

A bar code is a bar code that is composed of bars and spaces of different widths and different reflectivities, and is coded according to a certain coding rule (code system) to express a set of digital or alphabetic symbol information.

A bar code is a set of parallel line patterns with different thickness and spacing according to certain rules. Common bar codes are composed of black bars (abbreviated as bars) and white bars (short for empty) with widely different reflectances.

Since objects of different colors have different wavelengths of visible light, white objects can reflect visible light of various wavelengths, and black objects absorb visible light of various wavelengths. Therefore, when the light emitted by the barcode scanner light passes through the aperture and the convex lens 1, When it is irradiated onto the black and white bar code, the reflected light is focused by the convex lens 2 and then irradiated onto the photoelectric converter.

Then, the photoelectric converter receives the reflected light signals having different strengths and weaknesses corresponding to the white bars and the black bars, and converts them into corresponding electrical signals and outputs them to the amplification shaping circuit. The widths of the white bars and the black bars are different.

The duration of the corresponding electrical signal is also different. However, the electrical signal corresponding to the strip and space of the bar code output by the photoelectric converter is generally only about 10 mV and cannot be used directly.

Therefore, the electric signal output from the photoelectric converter is first sent to the amplifier for amplification. The amplified electric signal is still an analog electric signal. In order to avoid the error signal caused by the defects and stains in the barcode, an shaping circuit needs to be added after the amplifying circuit. The analog signal is converted into a digital electrical signal so that the computer system can accurately interpret it.

The pulse digital signal of the shaping circuit is translated into digital and character information by the decoder. It discriminates the code system and the scanning direction of the bar code symbol by identifying the start and end characters; and discriminates by measuring the number of pulse digital electrical signals 0, 1. The number of strips and spaces. The width of the strips and spaces is determined by measuring the duration of the 0 and 1 signals.

In this way, the number of bars and spaces of the bar code symbol being read and the corresponding width and the code system used are obtained. According to the coding rule corresponding to the code system, the bar symbol can be replaced with the corresponding number and character information. The interface circuit is sent to the supermarket cash register system for data processing and management, and the entire process of bar code reading is completed.

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