PCB Tech - Design of Wireless Sensor Network Monitoring System for PCB board Electroplating Current

Using computer, sensor technology and wireless communication, this paper designs a wireless sensor network monitoring system for PCB board electroplating current detection. The monitoring system uses NRF9E5 microcontroller as the wireless sensor node, and uses the design of Hall current sensor and detection circuit to realize the wireless communication between the wireless sensor node and the computer.

The main function of the PCB board is to make various electronic components form the connection of the predetermined circuit, the quality of which will directly affect the performance of the entire electromechanical product. PCB electroplating current is one of the important factors affecting the quality of PCB boards. At present, the detection of PBC electroplating current is carried out by operators holding hand-held monitoring equipment at certain intervals; therefore, there are many shortcomings, such as non-real-time detection, easy to leak Detection and false detection, long-term work in the electroplating environment will damage human health, etc. In view of the fact that manual detection can no longer meet the needs of the development of today's manufacturing technology, this paper proposes a wireless transmission scheme for PCB electroplating current, that is, placing sensor nodes where the electroplating current needs to be detected, and the monitoring center will conduct unified real-time monitoring and monitoring of the collected current data. control.

1. System framework

The structure of PCB electroplating current monitoring system based on wireless sensor network, which can be divided into three layers: data acquisition layer, system communication layer and management layer. The framework of PCB electroplating current monitoring system based on wireless sensor network: the data acquisition layer is the layer of the whole system, which consists of sensor nodes and sink nodes placed in the working environment. Through the built-in data acquisition unit, the sensor node can collect the current signal flowing through the PCB board, and after data processing, send it to the sink node by wireless communication; the sink node aggregates, analyzes and stores the data sent by the sensor node, And wait for the computer's command, ready to communicate with the computer. The system communication layer refers to the communication between the convergence node and the computer, and adopts the RS232 serial communication mode. By setting P0_ALT. 1=1, P0_DIR. 1=l, select the second function of the P01 and P02 pins of NRF9E5 as the RXD and TXD of the serial port, and use the chip MAX232 to perform level conversion and connect to the serial port of the computer to process the data collected from each node and send it through the main module. The control instructions and valid data complete the setting of each node and realize the control of the field equipment. The management layer is a process in which the computer analyzes and processes the collected electroplating current data. The computer can collect the current data of the installed Hall sensor nodes according to the needs of the administrator, and complete various management functions such as data processing, chart display, control and storage; when the current flowing through the PCB board exceeds or falls below the given value range, The system gives sound and light alarm.

2. System hardware and design
The wireless sensor node is the basic unit of the entire wireless network. Its main task is to collect PCB electroplating current data, pre-process the data, respond to commands from the host computer, and then send the collected current data to the host computer. . The wireless sensor node is composed of NRF9E5 microcontroller system, wireless communication unit, sensor unit and indicator light alarm circuit.

2.1 Wireless communication unit
Because the NRF9E5 wireless microcontroller has built-in 433MHz, 868MHz, 915MHz transceivers of NRF905, the design of the whole system is more concise and reliable. Through software programming, the transceiver can automatically complete functions such as sending, receiving and monitoring. From the perspective of system design, it is only necessary to interpret and control the data in the data packet by software.

2.2 Sensor unit
The sensor unit is mainly responsible for the collection of current information, which is the basis for ensuring the performance of the entire system. First of all, it is necessary to convert the current signal into a voltage signal. Here, the TBC-LTA series Hall current sensor is used. Its working power supply voltage is ±(12~15)V, and its working temperature is -40~85 degree Celsius. In order to improve the measurement accuracy, combined with the actual measured current value, this paper selects the TDC503LTA sensor in the TBC-LTA series of DC current sensors. The NRF9E5 contains a 10-bit linear AD converter with a conversion rate of 80kS/s. The reference voltage of the AD converter can be selected by software as Aref input or internal bandgap reference voltage of 1.22V. The AD converter has 5 inputs that can be selected by software, its typical application is start/stop mode, and the sampling time is controlled by software. It is 10-bit by default, but can be set to 6-bit, 8-bit or 12-bit by software if required. At the same time, the AD converter can also be applied in differential mode. When AIN0 is used as the negative input terminal, AIN1-3 are used as the positive input terminal.

2.3 Indicator light alarm circuit
When the current flowing through the circuit board is lower than the lower limit value or higher than the upper limit value, the indicator light alarm circuit will generate an audible and visual alarm, so that managers can take immediate countermeasures. In this design, the red LED light and the speaker are used as the indicator light alarm circuit.

3. System software design
3.1 Software design of lower computer
In modern wireless communication, data is transmitted in packets. For wireless SoCs such as NRF9E5, each time data is sent and received in the form of data packets. The data packet format is an important part of the communication protocol. The wireless data packet formats of NRF9E5 are: Preamble, ADDR, PAYLOAD, CRC. Among them, Preamble is the preamble, which is automatically added by the hardware; ADDR sends 32-40-bit address code; PAYLOAD is valid data (32bit); CRC is the cyclic redundancy code checksum, which can be corrected by the built-in CRC error detection hardware The circuit is automatically added and can be set to 0, 8 or 16 bits. The important job of the sensor node is to send the collected data. To realize the wireless transmission of data, the wireless transceiver in the processor must be operated in the transmission mode. The transceiver (NRF905) of NRF9E5 has three working modes: ShockBurst receive (RX) mode, ShockBurst transmit (TX) mode and energy saving mode.

3.2 PC software design
The software design of the host computer uses VisualC++ for programming, and designs a current real-time display panel and a database for data storage. After the wireless sensor network layout is completed, the data of many sensor nodes are uploaded to the computer, and the computer program, that is, the host computer program, stores these data, which provides convenience for future data query and processing. VisualC++ provides users with three database access methods, such as ODBC, DAO and OLEDB. ODBC provides application programming interface (API), any database can achieve the purpose of database management through these APIs. The general procedure for using the ODBC database provided by MFCAppWizard is:
1) Create a database with database tools such as Access;
2) Define an ODBC data source in Windows for the database created by 1);
3) Select the data source defined above in the document application wizard of the create database process;
4) Design the interface and associate the controls with the data table fields.
In this design, a database is first established, and several data tables are established according to the number of sensor nodes, and then the ODBC classes provided by MFC: record set class, database class and visual record set class are used for programming, and each wireless sensor node is programmed. Uploaded data are stored in individual data tables according to their node numbers.

4. Conclusion
The wireless sensor node of this system is based on low-power NRF9E5 single-chip microcomputer, uses TBC-LTA series Hall current sensor, and integrates computer technology and wireless sensor network technology to perform real-time data acquisition and A/D conversion for PCB electroplating current, and The collected current data is analyzed and stored, which provides a good operating environment for monitoring the production of PCB electroplating current, improves the quality of the PCB board, and enhances the competitiveness of the product. This system has the characteristics of low cost, low power consumption, high detection accuracy, simple operation and humanization. It can solve the problem of PCB board electroplating current monitoring well, and has good application and development prospects.