Micropower Data Acquisition Using MSP430 MCU

0 Introduction

If the underwater data acquisition system with battery as power source is to work for a long time, it must be equipped with a large number of batteries as power source. If the power consumption of the system can be reduced, the number of batteries will be reduced, which can not only reduce the cost of the system but also greatly reduce the volume and weight of the system, and is more conducive to the deployment of the underwater data acquisition system. This paper introduces the design and implementation of an underwater micro-power data acquisition system based on the micro-power single-chip microcomputer MSP430F1611 and CF card, with a total power of only 150mW. Compared with the traditional data acquisition system with DSP as processor and IDE hard disk as storage medium, the power consumption is greatly reduced.

1 Overall system composition

This system is used in the vector hydrophone noise measurement test, which requires real-time acquisition and storage of the vector hydrophone 4-channel signal, with a sampling rate of 10kHz for each channel and working continuously underwater for 7 hours.

Since the sampling rate of this system is not high, the total amount of data in 7 hours does not exceed 2G, so there is no need to use IDE hard disks with high power consumption and volume. A CF card with a capacity of 2G can fully meet the system requirements. The full name of CF card is Compact Flash, which is compatible with 3.3V and 5V operating voltages. There are no moving parts when working. It is small in size, low in power consumption, and large in capacity, and has a high cost performance. At present, the capacity of CF card can be as high as 12GB. CF card consists of a control chip and a flash memory module. The flash memory is used to store information, and the control chip is used to achieve connection with the host and data transmission. CF card can work in TRUEIDE mode and is fully compatible with ordinary IDE hard disk interface, so it is very easy to develop and use.

The system only stores the collected data without signal processing, so there is no need to pursue high speed in the selection of processors. This system uses TI's ultra-low power single-chip microcomputer MSP430F1611 as the system processor, which is responsible for AD collection and writes the collected data into the CF card. This is a cost-effective single-chip microcomputer with the following characteristics: rich on-chip peripherals; ultra-low power consumption, with an operating current of only 600μA at a voltage of 3.3V and a main frequency of 1MHz; powerful processing capabilities, with an instruction cycle of 125ns under an 8MHz crystal drive, which fully meets the processing requirements of the system. The overall structure of the system is shown in Figure 1.

2 Hardware Design

2.1 CF card interface design

CF supports three basic working modes: PC Card Memory mode, PC Card I/O mode and True IDE mode. In the design of this article, True IDE mode is used, which can be automatically entered when the CF card is powered on. Before inserting the CF card, ensure that the I/OE pin of the CF card slot is low, which can make the CF card enter True IDE mode. The interface diagram between the microcontroller and the CF card is shown in Figure 2.

MSP430F1611 has six independently configurable bidirectional 8-bit I/O ports (P1~P6). In this design, the P1.0 and P1.1 pins of the P1 port are connected to the read and write signal lines IORD and IOWR of the CF card respectively; the reset signal RESET is given by P1.2; A0~A2 are data, command or status register address lines, which are controlled by the microcontroller P1.3~P1.5 pins. The CF card has a total of 16 data lines D[15:0], but it can be set by software to work in 16-bit mode or 8-bit mode. Since the data line width of the MSP430F1611 microcontroller is 8 bits, it is designed to work in 8-bit mode in the hardware, using D0~D7 as data lines, connected to the P2 port of the microcontroller, and D8~D15 are left floating.

2.2 AD acquisition module design

In order to reduce the power consumption of the system, under the premise of our system index requirements, the selection of ADC devices should try to use low-power ADC devices. In the design, we used the AD7655 of ADI Company of the United States. This ADC consumes only 2.6mW when the sampling rate is 10kSPS, has four analog input channels, the accuracy is 16bit, and the maximum sampling rate is up to 1MSPS. The data output interface supports both serial and parallel modes, which can be easily connected with processors such as microcontrollers and DSPs. The specific hardware interface diagram of AD and microcontroller is shown in Figure 3.

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When reading and writing sectors, you first need to set the LBA address of the starting sector and the number of sectors, and set the command register. Set the command "20H" for reading data and "30H" for writing data. Then read the status register to determine whether the status register is "58H". If it is, start the read and write operation; if not, continue to read the status register. Next, read whether the status register is "50H" to determine whether the CF card operation is completed. If not, continue to read and judge; if yes, end the read and write process. If a timeout or error occurs in the judgment status register, set the timeout or error flag and jump out of the read and write process. Figure 4 is a flow chart of reading and writing a sector of a CF card.

Since the operation on the CF card is based on sector bit units, two buffers of 1 kByte size are opened in the internal RAM of the microcontroller. The data in each buffer can just fill up two sectors of the CF card. The data collected by AD is first stored in the buffer. When one buffer is full, the CF LBA address, sector number and write command are set to write the data in the buffer to the CF card. At the same time, the data collected by AD is stored in another buffer.

If the CF card is to read data directly on the computer through a card reader, the file system in the CF card must be consistent with the file system of the computer. The current file systems of computers include FATl6, FAT32 and NTFS. Due to the limited processing power of micro-power microcontrollers, there is not much time left after completing the data acquisition and data storage work within the sampling period. If a program for processing the file system is added, it will inevitably affect the real-time performance of the system data acquisition. In the program of this design, the data is not written into the file system, but the data is written into the sector from small to large starting from the LBA address corresponding to the data sector until the entire CF card is filled. When reading data, a small VC program is written using the disk operation function to read the data in the CF card in turn and save it as a file in the computer's hard disk. The size of the read sector and file can also be easily set, which is very flexible. In this way, real-time data acquisition and storage of the system is realized under the condition of limited processor power.

4 Conclusion

This design method greatly reduces the power consumption of the entire acquisition system. According to the measurement, the power consumption of the entire system is 150mW. The use of high-energy lithium-ion batteries as the system power supply allows the entire system to be easily installed in a cylindrical sealed tank with an inner diameter of 15cm and a height of 15cm. The reduction in volume is also more conducive to the deployment of the system underwater. After being tested in Songhua Lake, Jilin, the system can work stably and reliably, and collect and store the noise data of the underwater environment and the noise of passing ships in real time.