Abstract : This paper introduces the design and implementation of a low-power oil well data acquisition system based on nRF905. Keywords : nRF905 wireless transceiver; C8051F; low power consumption; frequency division multiple access; USB Introduction Oil fields have numerous wells distributed over areas ranging from tens to hundreds of square kilometers, and their distribution is relatively scattered. Some water injection and steam injection wells lack power supply and dedicated personnel for on-site monitoring. Currently, most wells are inspected manually, with workers periodically checking equipment operation and recording oil production data. Previously used instruments were cumbersome to operate, requiring valve closure for sensor installation, and sensor removal after measurement to prevent loss, resulting in high labor intensity and affecting the accuracy of oil production data. This system uses an nRF905 wireless transceiver for data acquisition. The on-site intelligent transmitter is battery-powered, with low power consumption, and can operate continuously for more than a year without external power. Furthermore, the transmitter has a special anti-theft design, making it impossible to remove without specialized tools. Workers can receive transmitter information within a 50-meter range using a handheld data acquisition device, without even stopping the machine, and the information is displayed on an LCD screen. Measurements are automatically stored after completion. An alarm will be triggered when the data exceeds the normal range. The management computer reads the stored measurement data and stores it in the database via the USB interface of the handheld data acquisition unit. The data acquisition system block diagram is shown in Figure 1. Figure 1: Data Acquisition System Block Diagram Hardware Design The intelligent transmitter hardware uses a C8051F350 microcontroller and an nRF905 RF module that support low-power operation, a 32768Hz low-frequency crystal oscillator, and is powered by a single AA lithium battery. Figure 2 shows the block diagram of the intelligent transmitter. Figure 2: Intelligent Transmitter Block Diagram The handheld data acquisition unit hardware uses a C8051F340 microcontroller with a USB interface that supports low-power operation, an nRF905 RF module, memory, a real-time clock, and a charging circuit. It uses a 32768Hz low-frequency crystal oscillator and is powered by a rechargeable 260mAh lithium battery. Figure 3 shows the block diagram of the handheld data acquisition unit. [align=center]Figure 3 Block Diagram of Handheld Data Acquisition Unit[/align] The C8051F350 is a precision mixed-signal microcontroller from Silabs. It features an 8-channel 24-bit SD-type ADC, a 128x PGA, a current-mode DAC, VREF, and other analog peripherals, allowing for easy direct connection to sensors such as temperature and pressure sensors. The current-mode DAC excites the sensor, and the sensor's output signal is amplified by the on-chip 128x PGA before A/D conversion, eliminating the need for additional signal conditioning circuitry. It has 8K of on-chip FLASH memory, which can be programmed and rewritten in-system. Sensor calibration parameters can be stored in the FLASH, saving on external memory. The C8051F340 is a microcontroller from Silabs with a USB 2.0 interface, supporting full-speed (12Mbps) and low-speed (1.5Mbps) modes; it includes a dedicated 1KByte USB buffer memory; and it integrates a USB transceiver, eliminating the need for external resistors. The nRF905 features 64K Flash program memory and 4352Byte data RAM; it operates on a 2.7–5.25V power supply and can be directly powered via a USB interface. Its processing speed reaches 48MIPS, sufficient for handheld data acquisition devices. The nRF905 is a monolithic RF transceiver from Nordic VLSI of Norway. It operates at low voltage and consumes very little power, operating in three ISM bands: 433/868/915MHz. Within each band, it supports multiple channels with a switching time of less than 650ms. This characteristic allows for the use of frequency division multiple access (FDMA) to enable multiple sensors to work together without interference, eliminating the need for complex protocols. The ShockBurst mode automatically handles header processing and CRC (Cyclic Redundancy Check). It communicates with a microcontroller via SPI serial port, eliminating the need for a more powerful microcontroller and simplifying software design and reducing hardware costs. It is very easy to use and features built-in idle and power-off modes for easy energy saving. The nRF905 is suitable for various fields such as wireless data communication, automotive, and remote sensing. Antenna design is a crucial aspect of the entire system design. The nRF905 supports the use of PCB loop differential antennas, saving space and reducing production costs. The application schematic is shown in Figure 4. [align=center]Figure 4 Circuit Schematic of nRF905 and MCU[/align] The handheld data acquisition unit hardware also includes off-chip memory and a real-time clock circuit. The off-chip memory uses Microchip's 24AA series, with an I2C interface, a minimum operating voltage of 1.8V, and a standby current of 1mA. The real-time clock uses NXP's PCF8563T, with an I2C interface, a minimum operating voltage of 1.0V, and a minimum operating current of 0.25mA. This is ideal for low-power battery-powered applications. The handheld data acquisition unit uses a dedicated lithium-ion charging management chip to manage battery charging. Charging automatically begins after USB connection. A battery voltage monitoring module is added to the software to prevent excessive charging time. Software Design The software was developed using C language under Keil uVision2. The C8051F series features a hardware SPI interface, simplifying the development of the nRF905 driver. The nRF905 driver includes common functions such as initialization, data packet reading and writing, channel setting, and power setting. After debugging, it is packaged into a function library for use by smart transmitters and handheld data acquisition units. Smart Transmitter Software In addition to the nRF905 driver, the smart transmitter software consists of an A/D conversion module, a sensor calibration module, a timed wake-up module, and a main function. Upon power-up, the main function runs at high speed, performing initialization, A/D sampling, and controlling the nRF905 to send acquired data. It then switches to a low-speed power-saving mode, sleeps for a period, and wakes up to repeat the above process. The ratio of operating time to sleep time is 1:100, with an average current of approximately 50mA. Theoretically, a 2100mAh battery can last for 4.7 years. Handheld Data Acquisition Unit Software The software design of a handheld data acquisition unit is relatively complex. Besides the nRF905 driver, it requires writing USB drivers, LCD drivers, button drivers, clock modules, battery voltage detection modules, PCA timing modules, data read/write modules, file systems (data storage, compression, and retrieval modules), and command interpretation modules for the main program to call. The main program is an event-driven task scheduler that executes modules according to pre-set priorities. When no events occur, the main program switches to a low-speed power-saving mode, shutting down all functional modules except the real-time clock, consuming very little current until an external event wakes it up. External events that can wake up the main program include USB interface connection or disconnection, button events, and timer events. If the main program is woken up by a USB interface connection event, the microcontroller runs at its highest speed (48MHz) to execute the USB driver initialization and connection tasks, connecting with the host and performing predetermined functions according to commands sent by the host. If there is no data communication with the host for a specified time, the main program automatically enters standby mode. At this point, only the battery voltage detection module and the real-time clock module are operational until a USB disconnection event occurs. At this time, the main program will uninstall the USB driver and disconnect from the host. The software design supports changing the nRF905 channel during operation to support multiple smart sensors working together within a working area (communication radius, 50-100M). Measurement data from the field smart transmitters is read sequentially according to the set frequency and automatically stored. Stored information includes measurement time, transmitter serial number, test data, transmitter status, etc. Daily test data is compiled into a file, which can be queried locally or transferred to the management computer via USB for analysis and storage. Management Computer Processing Software To manage the acquired data, a user-friendly human-machine interface needs to be established on the host. Visual Basic (VB) is used to design the human-machine interface and develop the application. The USB driver control and instructions are encapsulated in functions to achieve serial communication between the PC and the handheld data acquisition unit. Specifically, this includes: initializing and driving the system to start working, actively searching for USB devices, completing the connection, and displaying the command execution status and the address of the found device; controlling communication with the USB devices, processing the received data, refreshing the data in real time, and displaying the measurement results of temperature, humidity, and pressure sensors. Other controls are used to analyze, display, and operate the data from the wireless smart sensors. Each smart transmitter has a unique serial number, and the management computer's database contains detailed information about the corresponding transmitter, such as transmitter type, production time, installation time, installation location, range, and maintenance records. Functions such as querying historical data and curves based on the serial number are provided. Each handheld data acquisition unit also has a unique serial number. The acquisition unit can read measurement data from multiple smart transmitters, and managers can evaluate operators' work based on the transmitter serial numbers and acquisition time in the acquired data. Conclusion The low-power oil well data acquisition system based on nRF905 designed by the author has advantages such as simple installation, low system investment, strong scalability, and low usage and maintenance costs. It greatly improves the efficiency and reliability of data acquisition and realizes the automation of parameter measurement. Where conditions permit, the system can also be combined with other technologies such as GPRS and the Internet to achieve fully automated measurement without human intervention. Currently, the system has been applied in various locations in Daqing Oilfield, including water injection well pressure measurement and gas pipeline pressure measurement, and the system operates reliably and stably.