基于低功耗的MSP430单片机的水下声音探测仪的发展-外文翻译论文.docx

南京航空航天大学金城学院毕业设计（论文）外文文献翻译系 部自动化专 业电气工程极其自动化学生姓名李泽宇学号2013071121指导教师张燕职称讲师2017年 5月 Development of MSP430-based ultra-low power expandable underwater acoustic recorder1. Introduction When studying underwater acoustics in an indoor laboratory setup, signal acquisition generally does not pose problems because many off-the-shelf products are available for a range of configurations and applications. These solutions are generally implemented on a PC or a rugged industrial chassis. Moreover, electric power supply, data storage and communications are assumed to be handy and unlimited. However, when investigating acoustics in the underwater environment, all these conditions are either too expensive or im-pssible. A feasible approach for underwater instruments must overcome these constraints. Ocean environment is full of noises from a variety of sources. A broad band of acoustic signals, from several Hz to several hundred kHz, can be found (Wenz, 1962). For example,marine mammals make sounds in frequencies ranging from 100Hz to 150kHz (Au, 1993).Raindrops falling on the sea surface create bubbles which generate loud noises in the range of 150kHz as they collapse (Nystuen, 2001). Ship traffic radiates noise from 1 to 10kHz (Corcker,1998). To study these ocean acoustic phenomena, sound is measured in he field and then analyzed in situ or post-processed in the laboratory. For measuring sound in the field,if the site is not far from the shore, a cabled system is generally adopted. However, deployment and maintenance of cable systems is costly. Moreover, coastal aters are generally full of human activities, subjecting underwater cables to the constant risk of being damaged by trawling and anchoring.For both cabled or stand-alone systems, the ocean environment poses challenges for power supply, data storage, and system stability. If the study site is too far from the coast, too deep, or too costly for a cabled system, stand-alone and self-contained logging systems are deployed on the seafloor. Regular service is needed to retrieve data and replace the battery pack.To address these problems, Ma and Nystuen (2005) developedan autonomous acoustic recorder called Passive Aquatic Listeners (PALs). This instrument consists of a microprocessor, a low-noise 10/20dBamplifier board, a hydrophone, and a battery pack. The microprocessor is a low-power Per sistor micro controller which has 8 channels of 10-bit AD, 16 I/Os, and a CF card interface for data storage. The system was designed to record rainfall acoustic spectrum in the ocean for up to one year. In order to achieve long-duration measurement, PAL normally stays in sleep mode to save power. It wakes up once every one or two minutes (programmable) to measure environment noise at a 100kHz sampling rate for 4.5s to obtain the spectrum. If the spectrum contains the signature of rainfall, the system will pick up the hydrophone signal, calculate, and store the spectrum continuously until the rainfall signature vanishes from the spectrum. To reduce the size of the memory storage needed, the system does not save the signal time series but only the spectrum. The 10/20dB amplifier board also provides options to capture the signal with appropriate scale. Taking this project as an example, we can see the issues of power and memory management are core issues for long-term deployment instruments.To record acoustic signals continuously in the ocean, Wiggins (2003) developed a low-power, high-data capacity autonomous acoustic recorder called the Autonomous Acoustic Recording Package (ARP). ARP consists of an OS500 data logger manufac-tured by Ocean Sensor Corporation, a hydrophone, two 36GB SCSI disks for data storage and battery packs. Given the large capacity of the SCSI hard disk drives, memory constraints are not an issue.The power consumption of the OS500 and hydrophone are approximately 600mW without the SCSI disk drives. The battery packs consist of two lithium batteries, a 580Ah (ampere-hour)/10V for the OS500 data logger, and a 135Ah/17V for the SCSI disk drives. The system provides a 1000Hz sampling rate, and supports long-term deployments of up to one year.Burgess et al. (1998) developed a low-power autonomous recording system, called CAP, 36cm long and 10cm diameter. It is capable of withstanding depths of 2000m and records acoustic signals at 5kHz for up to 10h, along with temperature and depthlogging. This device is so compact that it can be tagged on marinemammals to study their behavior. Later, CAP was upgraded to aneven more compact and power-efficient version called Bioprobe.The acoustic sampling rate of the new model can be set to anynumber between 100Hz and 20kHz with 16-bit resolution. Thesystem uses flash-memory as the data storage medium, and isthus more power efficient. With a 1.5Ah/3.6V alkaline cell, it canoperate at a 2kHz acoustic sampling rate for up to 41h. Thodeet al. (2006) used the design of the Bioprobe as the core of loggingdevices in a four-element vertical array to record and track marinemammals. Recently, other projects have applied the Bioprobe architecturein developing a new generation of compact and ultra-low poweracoustic loggers for marine mammal protection (Johnson andTyack, 2003; Madsen and Wahlberg, 2007).For marine mammal monitoring, Wiggins and Hilderbrand(2007) used a 32-bit, 20MHz microcontroller as the platform toconstruct a long term (months) and broadband (200kHz)autonomous underwater acoustic recorder. Because the monitor-ing needs to record continuously at a high sampling rate,data storage volume and battery power pack capacity are twochallenging engineering problems. Their solution was an arrayof laptop 2.5 00 disk drives (1.9TB) as the storage medium. Tomanage power efficiently, the data are stored in a 32MB RAMbuffer prior to streaming to the disk drives. Using this technique,only one drive in the array is activated for a short period of writingtime. Power consumption is thus reduced substantially.A recent development is Ecological Acoustic Recorder (EAR)of Lammers et al. (2008), which monitors biological activityon coral reefs and in surrounding waters. This microprocessor-based autonomous recorder samples the ambient sound fieldperiodically and automatically detects sounds which meet certaincriteria. With several power packs (each power pack consistsof seven high-capacity alkaline D-cell in series), the system canoperate up to one year. With its programmable recording dutycycle and power pack module arrangement, the system can beeasily configured to meet different needs of environmentmonitoring projects. The aforementioned projects show that engineers must tradeoff among long-term deployment, sampling rate, and data storagecapacity when constructing stand-alone, non-cabled underwaterlogging systems. High sampling rates and long operating periodsrequire greater data storage and high-performance microproces-sors. This in turn creates demand for large disk drives thatconsume more power. The resulting large battery packs increasethe size and weight of the system, impairing its portability.Fortunately, ongoing developments in microprocessors and flash-memory based storage have created new possibilities for thedevelopment of stand-alone, non-cabled underwater loggingsystems. One of the new generation of ultra-low power microcontrollersis the MSP430 MCU (Micro Controller Unit) from Texas Instru-ments. It is specifically designed for battery-operated productslike MP3 players, hand-held meters, and medical equipment.Its architecture significantly reduces both power consumptionand the complexity of peripheral circuits. In this research we usethe MSP430 MCU to design an architecture which is scalableand expandable in sampling rate, data storage, and numberof digitizing channels, at milliwatt power levels. We call it theUltra-Low Power Expandable Acoustic Recorder (UPEAR).2. Hardware architecture The performance of data logging systems is usually limited bythe bottlenecks of AD conversion speed and data streaming rate.Our design strategy is to fully exploit a single ultra-low powerMCU, rather than using a more powerful microprocessor or DSP.To overcome the challenges of high-speed data acquisition andstreaming, not only a fast AD conversion circuit, but also aneffective way to continuously stream data into a storage mediumwithout interrupt is needed. Streaming large quantities of datainto a storage medium is generally achieved by adoptinga powerful CPU and a high-speed data bus. This inevitablyintroduces complicated architecture and consumes more power.Such an approach is not an optimum solution for low powerstand-alone systems. The MSP430 MCU has a series of models with different numberof AD channels, digital I/Os, buffer and flash-memory sizes, andoptional peripherals such as LCD drivers. Compact in size, theyare extremely low in power consumption, ranging from roughly10mW in the active mode to less than a fraction of a mW in sleepmode. All models come in different packaging formats, includingQFN, LQFP, SSOP, and DIP. They can be as small as 12?12?1.5mm. Many MSP430 models have a 100kHz AD sampling rate,sufficient to meet the requirement for underwater acousticrecording, since ocean environmental noise is generally lowerthan 50kHz (Wenz, 1962). The unit cost for an MSP430 MCU isalso low, less than 10 USD a piece for most models. The MSP430 isthus very cost-effective compared with PC- or DSP-based solu-tions. However, a single MSP430 MCU does not have the capacityto execute all the tasks (multi-channel AD conversion, real-timeclock stamping, and data streaming) needed for a data acquisitionsystem running at a high sampling rate. We thus use multipleMSP430 MCUs to construct a master-slave architecture which isboth scalable and expandable.2.1. Slave unit A slave unit consists of a MSP430-F169 MCU and a SecureDigital (SD) memory card. Its schematic is shown in Fig. 1. Thesignal is digitized using the MSP430s built-in 12-bit Analog-to-Digital converter and then streamed to an SD card (TexasInstruments Corporation, 2003). The SD card is a removableflash-based storage device (SanDisk Corporation, 2003). Itsspecifications were originally defined by Toshiba Corporation,SanDisk Corporation, and Matsushita Electric Company for variousconsumer electronics such as digital cameras, PDA, mobile phonesand portable music devices. It is compact, simple, large incapacity, low in power consumption and low cost, an idealsolution for our design (Hsiao, et al., 2006, 2007). MSP430s.Universal Synchronous/Asynchronous Receive/Transmit (USART)communicates with the SD card via Serial Peripheral Interface(SPI). SPI is a synchronous serial protocol for interfacingperipheral devices with microcontrollers in a simple manner.As shown in Fig. 2, only four pins are needed for transferringdata between the MCU and the SD card (Texas InstrumentsCorporation, 2006). Upon power up, the MSP430 reads the first 512 bytes (definedas a block) of the SD card to retrieve the memory usage prior tothe current power cycle. This information is used to allocate freememory space for storing the upcoming new recording event.In other words, during each power cycle, the system will initiatea new clip automatically. The MSP430 then switches to sleepmode to preserve electricity. It stays in this low power mode untilawakened by sampling/storing trigger commands coming fromthe master unit, described in the next subsection. To ensure the success of simultaneous A/D conversion and datastreaming, a double-buffer structure is adopted along with DirectMemory Access (DMA). DMA is a module component of MSP430microcontroller family. It can transfer data between MCU memoryand peripherals without CPU intervention. MSP430-F169 has 2kbytes of random access memory (RAM). One kilo bytes are used toconstruct two buffers, denoted as Buffer I and Buffer II, 512 byteseach. MSP430 digitizes the signal and stores the results intothe buffer sequentially. A subprogram monitors the growth of thebuffers. Once Buffer I is full, its contents will be dumped into theSD card using DMA while the digitization continues streamingresults into Buffer II. Tasks are thus rotated between Buffers Iand II. With this arrangement, the acoustic signal is sampledcontinuously in each slave device which serves as a basic digitalrecorder that works on simple tasks (sample/store) by itself.According to our test, the slave unit takes 0.02ms to stream thedata buffer into the SD card, meaning a single slave unit canhandle digitization and logging up to 50k samples per second.Each SD card is enabled by pulling down its SELECT pin toground. With proper multiplexing circuitry and data storagemanagement, multiple SDs can thus easily be daisy chained toexpand the data storage capacity.2.2. Master unit A master unit consists of two MSP430-F169s, denoted as M1and M2, and an Real-Time Clock (RTC) chip DS1302 (shown inFig. 3). The DS1302 operates on very low power consumption.With a single 3.3V coin battery cell, it can run for years withoutlosing time (Dallas Semiconductors Corporation, 2005). When thepower is turned on, M1 starts communicating with the RTC viathree I/Os to retrieve the current clock time. M1 sends the clock tothe slave units via general I/O ports. In total 26 I/O ports are used.For example, the month is represented by a number between 1and 12, requiring four ports. Similarly, it takes 5 ports for the day,5 ports for the hour, 6 ports for the minute and 6 ports for thesecond. The year is skipped because we ran short of I/O ports onthe MSP430-F169. However the year can be easily managed inthe users experiment logbook. For the next generation, we mayuse another MSP430 model which provides more I/O ports toaccommodate the year information in the time stamp. The RTCDS1302 is an inexpensive product, very popular in consumerelectronics. It is synchronized to GPS before deployment but it drifts several seconds per day. For this prototype, we only use its clock to have an approximate time of the recording. In thenext generation of development, we will use SeaScan Real TimeClock (SEASCAN INC.) which drifts less than 1 second per year.Nevertheless, with the master-slave configuration, all the recei-vers get the same sample-and-hold command from the master I/Oport. The difference in actual sampling time between channels isless than 125 nano-seconds, accurate enough for the beamform-ing of the array. M2 is in charge of the overall coordination and synchronizationof the slave units. It can operate in either standby mode, delay-time mode. For the former, it waits for the start command from anexternal trigger; for the latter, it wakes up to work at a pre-programmed time. For diver deployment, the system does notneed to be turned on until all the preparations have beencomple