“This wireless scanner takes the microcontroller mPSD3254BV as the core. It can scan one-dimensional or two-dimensional barcodes through the scanning subsystem. The keyboard and Display system are convenient for users to communicate with each other. The wireless transmission module can send the data collected on site to other devices. At the same time, the scanner can also store tens of thousands of data information. The whole system is powered by lithium batteries and can work continuously for 40 hours. When the collected data is abnormal, the system will automatically buzz and vibrate to remind the user. The system structure is shown in Figure 1.

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Authors: Zheng Jianfeng; Li Jin; Fan Dong

In the process of developing from industrial society to information society and from industrial economy to knowledge economy, automatic identification technology is playing an increasingly important role. In the business fields that require item identification, data scanning, and information logging, the use of automatic identification technology can improve the efficiency and reliability of item and related information management. Barcode data scanners are designed for this.

This wireless scanner takes the microcontroller mPSD3254BV as the core. It can scan one-dimensional or two-dimensional barcodes through the scanning subsystem. The keyboard and Display system are convenient for users to communicate with each other. The wireless transmission module can send the data collected on site to other devices. At the same time, the scanner can also store tens of thousands of data information. The whole system is powered by lithium batteries and can work continuously for 40 hours. When the collected data is abnormal, the system will automatically buzz and vibrate to remind the user. The system structure is shown in Figure 1.

Figure 1 System structure block diagram

hardware design

power module

The power module consists of two parts, 1AH lithium battery and power voltage regulator chip MAX604. The MAX604 chip is a low-dropout, low-power linear regulator, used to ensure the stability of the system operating voltage. With the increase of the usage time, the power of the lithium battery will gradually decrease, which cannot effectively guarantee the stable operation of the system. Therefore, a MAX604 is added at the back end of the lithium battery, and the voltage is always stable at 3.3V.

The OFF terminal on the MAX604 chip can be used to control whether the voltage regulator chip outputs voltage. When the OFF terminal is a high level “1”, the module has an output voltage; when the OFF terminal is a low level “0”, the module has no output voltage. The system utilizes this feature to realize power switch and sleep wake-up. Its hardware schematic diagram is shown in Figure 2.

Figure 2 Power control circuit

charging module

The charging module is used to charge the battery in time when the power of the battery is insufficient.

The power parameters of the lithium battery are: under normal circumstances, the voltage is 3.6V, and when the voltage is lower than 2.5V, the battery must be charged, and the highest charging voltage can reach 4.1V. In the system, the battery voltage should be detected in real time. When the battery voltage is too low, the user can be reminded to charge in time to prevent the battery from being damaged when the battery voltage is too low to continue using. This design uses LM317 components to form a circuit of constant current source charging mode, which detects the battery voltage in real time during the charging process. When the battery is fully charged, it can automatically cut off the power supply to prevent the battery from being damaged by overcharging. The switch of the charging power supply is controlled by MOS tube, thus avoiding the generation of sparks when using the relay switch, so that the scanner can meet the requirements of explosion-proof design.

wireless data transmission module

The wireless transmission module adopts STR-11 micro-power wireless data transmission module. The wireless module has the advantages of integrated reception and transmission, small size, few peripheral devices, built-in antenna, and can be directly connected to the MCU serial port. This scanner uses a TTL serial port of the mPSD3200 microcontroller to directly control this wireless transmission module. Usually the module is in a dormant state. When there is a wireless transmission request, the single-chip microcomputer activates it with an IO signal and responds to the wireless transmission request.

Barcode Scanning Module

The barcode scanning device selected by the system is the SE-923 II class laser scanning engine. The scan engine is small in size, light in weight, bright in brightness, and has the fastest scanning speed. The laser scanner has the characteristics of low power consumption, fast scanning speed, high precision, and automatic identification of one-dimensional barcodes.

This scanner uses another TTL serial port used by the mPSD3200 microcontroller to communicate directly with the scanning module. The user triggers the scan by pressing the button, and the scanning module sends the information of the one-dimensional or two-dimensional code to the microcontroller through the serial port. The scanning module sends a wrong voice prompt to the microcontroller when the scanning is unsuccessful; when the scanning module does not scan for a long time, the scanning module automatically switches to the sleep state to reduce power consumption.

keyboard input module

The scanner is designed with 28 keys in total; the PA and PB ports of the mPSD3200 microcontroller are set as common I/O interfaces to form a determinant keyboard matrix. Set PA0″6 to seven column lines, PB0″3 to four row lines, and set PA7 to be a logic input. Use the PA7 port to detect whether a key is pressed on the column line. When detecting that a key is pressed, PA7 applies for an interrupt to the CPU, and the CPU determines which key it is. The specific circuit is shown in Figure 3.

Figure 3 Keyboard control circuit

LCD display module

The LCD screen of this scanner adopts KS0741 chip, which has its own driver module. The interface between the driver module and the CPU has two control modes, serial or parallel. The scanner adopts parallel control mode. The LCD screen has low power consumption, and the operating current is only milliampere. It can display text and pictures, the LCD screen can display up to 8 × 16 Chinese characters. Various information can be displayed to the user.

Alarm prompt module

The alarm prompt module is mainly responsible for the sound and vibration prompts of the scanner. When the barcode scanner finishes scanning or makes an error, the scanner will give a corresponding sound or vibration prompt. The sounding device adopts a piezoelectric buzzer, which is driven by a push-pull circuit and can emit different sounds when square waves of different frequencies are loaded. The vibration device adopts a button-type motor, which is driven by a triode. When the triode is turned on, the button-type motor vibrates, so that the user can be reminded by the vibration of the scanner in a noisy environment.

Epilogue

The hardware design of the scanner system has passed the test, and the scanner can be operated with the corresponding system software program to realize the functions of bar code scanning, wireless data transmission, key input, LCD display and alarm prompt.

The scanner can not only store tens of thousands of pieces of information locally, but also communicate with the computer through wireless transmission or RS-232 serial port, which is convenient for users to manage the information.