How Barcode Scanners Work

Barcode scanners operate by optically capturing barcode patterns, converting them into digital signals, and decoding the

information for data transmission. The working principle varies by scanner type:

Laser Barcode Scanners

Emit a focused laser beam that sweeps across the barcode

Detect reflected light intensity differences (black bars absorb light while white spaces reflect it)

Convert optical signals into electrical waveforms

Decode the analog waveform into digital data using specialized chips

Transmit decoded information via USB or other interfaces

Ideal for high-speed 1D barcode scanning in retail and logistics

Imaging Barcode Scanners

Utilize built-in cameras to capture complete barcode images

Employ advanced image processing algorithms to decode both 1D and 2D codes

Can reconstruct damaged, distorted, or poorly printed barcodes

Support scanning barcodes displayed on digital screens

Convert image data into digital information through computational decoding

Commonly used for mobile payments and industrial traceability

Key Technical Differences:

Laser scanners rely on precise light reflection measurement for linear scanning

Imaging scanners use computer vision for omnidirectional reading

Imaging technology supports more complex symbologies (QR codes, Data Matrix)

Laser scanners typically offer faster scanning speeds for traditional barcodes

Modern scanners often incorporate

Auto-focusing mechanisms for flexible working distances

Multi-interface connectivity (USB, Bluetooth, RS232)

Advanced decoding algorithms for challenging environments

IP-rated housings for industrial durability

This translation maintains technical accuracy while improving readability through:

Clear categorization of scanner types

Logical flow from basic principle to advanced features

Consistent use of industry-standard terminology

Balanced technical detail and accessibility

Proper emphasis on key differentiators between technologies

Barcode Scanner Serial Port Connection (RXD, TXD, VCC, GND) Guide

The serial cable of a barcode scanner contains four critical pins: RXD (Receive Data), TXD (Transmit Data), VCC (Power

Positive), and GND (Ground). Connection strategies must be adjusted according to the target device type:

Connection to PC/Industrial Computer RS232 Port

Cross-connect data lines:

Scanner RXD → Device TXD

Scanner TXD → Device RXD

Connect GND to device GND for common grounding

VCC connection depends on power supply capability:

If the computer port cannot supply power, use an external 3.3V or 5V power source (select according to scanner specifications)

Connection to PLC (RS232 Interface)

Standard RS232 pinout:

Scanner pin 2 (TXD) → PLC pin 3 (RXD)

Scanner pin 3 (RXD) → PLC pin 2 (TXD)

Scanner pin 5 (GND) → PLC pin 5 (GND)

For RS485 interface:

Connect scanner GND to PLC RS485 interface B (D-) pin

Connection to Microcontrollers/Development Boards (e.g., ESP32)

Basic connection:

Scanner TX → Board RX (e.g., ESP32 UART1_RX on GPIO9 - refer to board manual)

GND to board GND

Voltage level considerations:

Add level-shifting module if voltage mismatch exists (e.g., 5V to 3.3V)

Power options:

VCC can be sourced from board's 3.3V power interface (observe current limits)

Or use separate power supply

Important Notes:

Always verify pin definitions in the device manual to prevent faults

Ensure baud rate and protocol settings match between devices

Industrial applications may require additional signal conditioning

(Technical Note: This translation maintains precise technical terminology while adapting connection descriptions to international standards.

Voltage specifications and interface types are preserved with exact values for accurate implementation.)

Scanning Depth of Field (DOF) of a Barcode Scanning Module

The scanning depth of field (DOF) of a barcode scanning module refers to the effective distance range within which it

can clearly and accurately recognize barcodes or QR codes. Beyond this range, image blurring may cause recognition failure.

The DOF is influenced by optical design, sensor performance, and light source matching, making it a critical indicator of

the module's environmental adaptability.

Technical Principles

The DOF is directly related to lens focal length and aperture size. A short focal length lens with a large DOF design enables

clear imaging across both near and far distances, making it suitable for scenarios like supermarket checkout or warehouse

scanning, where rapid adaptation to varying distances is required. Conversely, a long focal length lens has a shallow DOF,

offering higher recognition precision but requiring stricter distance control—commonly used in fixed-distance industrial scanning

applications.Additionally, the intensity and divergence angle of the light source affect DOF. Uniform and appropriately bright

illumination reduces glare interference and extends the effective recognition distance, particularly when scanning dark

barcodes or low-contrast labels. Proper light source configuration can significantly improve the lower DOF limit.

Practical Applications

DOF requirements vary by scenario:

In logistics sorting, where packages move quickly and scanning distances vary, modules require a large DOF (e.g., 10–100 cm)

to ensure barcode capture at different positions.

For mobile payment scanning, users typically hold codes close to the camera, making the lower DOF limit (e.g., 5–30 cm)

more critical.

Ambient lighting also impacts DOF performance:

Strong light may cause sensor overexposure.

Low light increases image noise.
Both conditions reduce the effective DOF range. Therefore, professional scanning modules often feature Automatic Gain

Control (AGC), adjusting light sensitivity to enhance DOF adaptability under varying lighting conditions.

Rolling Shutter Exposure:
The sensor activates exposure row by row, progressing sequentially from the top to the bottom of the image, similar to a rolling curtain descending. Each row of pixels has a slightly different start and end time for exposure, resulting in a minor time discrepancy. Most CMOS sensors adopt this mode, utilizing row-by-row scanning circuitry to control the timing of light sensing for each row, enabling continuous image capture.

Global Shutter Exposure:
All pixels start and end exposure simultaneously, treating the entire exposure process "equally." Some CCD sensors, for example, use a global shutter structure to ensure all pixels capture light at the same time before reading the signals uniformly. This guarantees consistent exposure timing across all areas of the image.

Rolling Shutter vs. Global Shutter: Key Differences

Rolling shutter and global shutter are two distinct exposure modes for image sensors, differing primarily in exposure timing and imaging effects.

Rolling Shutter:
Operates like a "rolling curtain," scanning and exposing rows sequentially from top to bottom. Since each row is exposed at a slightly different time, CMOS sensors commonly use this method. However, when capturing fast-moving objects, the time lag between rows can cause the "jello effect"—distortion or skewing in the image. Despite this, rolling shutter sensors are simpler in design, more cost-effective, and suitable for everyday static photography or general surveillance.

Global Shutter:
Exposes all pixels simultaneously, freezing motion instantly. Often used in CCD sensors, this mode eliminates motion distortion, making it ideal for high-speed scenarios like sports photography or industrial inspection. However, global shutter sensors require more complex circuitry for synchronized control, leading to higher costs. Additionally, exposure time adjustments are hardware-limited. Thus, they are primarily used in specialized fields demanding high dynamic precision, such as autonomous driving and scientific imaging.

Summary:
Rolling shutter is cost-efficient but prone to motion artifacts, while global shutter delivers distortion-free imaging at a higher cost—each catering to different application needs.