The time of danger

1. Introduction

1.1 Research Purpose

Due to develoment technology, many facilities have been created with the aim of helping people in the time of danger. In such a situation each second may has the worth life of one person, the situation getting even harder at sea where the most of the accident or crashes are become tragedies.

MOB (Man over Board) is one of the most terrible nightmares that any mariner will ever have. Of course the role of training and following the certain rules (such as avoiding going to the ship deck at night lonely, obey chain of commands in critical situations or equipping with life jacket on deck) can't be skipped. But when MOB happens the most important thing is to locate and recover her/him as soon as possible.

The purpose of this thesis is to design and implement a set of devices which will have the great impact on the speed of process of surviving, guide the rescue squads to the exact position of the people in peril at sea, inform other ships and boats that a MOB (Man Over Board) incident has happened. Based on mentioned reasons, this set includes a transmitter which is embedded in the life jacket of voyagers and receivers which can be placed anywhere like cockpits in ships, ship stations, boats, helicopters. Following section will discuss about how the functionality and behavior of these devices should be beside figure1 illustrating these functionalities in the general view.

1.2 Problem statement

This section tries to answer some questions:

  • What is the problem?
  • The main problem is finding a way to improve the speed of process of surviving at sea in a more secure way. This can be done by merging the other alternatives which already exist, injecting some new ideas to them or in the other words trying to update them with the new technologies (how would be an MOB device if we wanted to invent it today by concerning current rules and protocols?).

  • What are the alternatives so far (related work)?
  • Traditional devices like personal ELTs (Emergency Locator Transmitter) [1] or handheld devices such as rescue laser flare are now becoming more complemented, specialized and organized; presented in the terms of MOB devices.

  • What is the new solution?
  • The new solution will automatically (by sensing humidity)/manually uses GPS satellite in order to locate the exact location of people who need to be rescued and send it to receiver side. Then this side tries to parse the received message, by using GPS satellite data locate it and guide the rescue squad to the location. By concerning these functionalities following tasks are defined for each side.


  • Retrieve the coordination point of the MOB, convert it to the radians and send it.
  • Send the time since the MOB device is activated.
  • Send a bit in order to indicate the existence of the satellite view. This option can indicates that is the coordination point is updated or old.
  • 16 bit CRC (Cyclic Redundancy Check) in order to validate the data.


  • Receive the coordination point of the MOB devices.
  • Retrieve the coordination point of the receiver device and calculate distance to the MOB device.
  • Calculate the direction to the MOB devices simultaneously.
  • And some other simple features like showing system clock, velocity, current coordination points and information of each MOB device.

Usually MOB devices works in two different ways:

Active: in this method MOB device always send a message back to the receiver in order to inform that the wearer is safe. In case of danger (e.g. man over board, fire, flooding) the connection will be aborted (degraded) or another type of message will be sent which trigger alarm system.

II. Passive: in this method receiver device always listens to MOB devices without transmitting. Once a massage is sent by transmitter emergency system will be activated. This method is in use in this product.

1.3 Existing Products

In order to clarifying the aims in the following section some similar devices which are already existed in the market will be considered.

1.3.1 ACR's Mini B 300 ILS H2ON [2]

This is a floatable, water/manual activated device with the working frequency of 121.5 MHz. embedded inline speaker emits audio warble in order to confirm distress signal transmission or notifying the receiver which there is a MOB condition. An LED is also trying to confirm signal transmission. It will be complemented with an ACR Vecta2 direction finder. The important thing about this device is using the 10 years storage life replaceable lithium camera battery. Operating life is at least 24 hours in -10?C.

1.3.2 Alert 2 Man-Overboard Alarm [3]:

This device consisting water activated transmitter with the effective range of 1 mile and working frequency of 418 MHz. In addition to audible alarm the receiver could wire to the engine in order to shut down in the MOB condition also by connecting a NMEA-compatible chart plotter the location of transmitter device can be coordinated. Transmitter device use two 3.6 volt lithium batteries. The remarkable thing of this model is the support of unlimited number of transmitters while others have.

1.3.3 Life Tag Wireless Man Overboard Monitoring System [4]:

Like the other devices this manufacturer produces a set of device which consists of transmitter and receiver.

The transmitter send a code back to the receiver permanently in order to confirm wearer is safe when the pendant beacon immerse to the water the signal will be degraded so it won't be safe anymore.

In the receiver part when the signal is degraded the alarm will be turned on, and the sinking person position monitored. In addition some critical information like the time of sinking or personal information of the sinking crew could be provided.

Transmitter beacon uses CR2 lithium batteries with the estimation of 200 working hours.

1.4 Target Specification

1.5 Research Methodology

The process of designing and Implementation of this project will start by introducing the ICs (Integrated Circuit) that are in used in this study and the way that they are manipulated. Third chapter focuses on software algorithms and the way of interacting with software. The process of test and implementation will be reviewed in the forth chapter. Finally conclusion as well as the further work will come on the chapter five.

This research has four main stages, first stage includes information gathering; for this stage literature survey as a part of qualitative approach has been done for understanding the market needs and what has been done in the same area as well as the related work. The second stage is dedicated to planning and preparing the environment for experiment. In the third stage quantitative approach is chosen because we deal with some numerical analysis and mathematical calculations and statistical analysis (please refer to chapter three in order to find out what has been done for mathematical calculations and the test and implementation chapter for details of statistical analysis).

2. Hardware Overview

2.1 Transmitter

As it was mentioned there are two different situations .the one which is transmitter need to consume power in most efficient way, because of limited source of power and source of danger as much as information transmit is better. In this project tried to use the most power efficient Integrated Circuit(IC) however in designing and programming of them this criterion was concerned. The figure 2.1 Illustrating the transmitter schematic and following by that every instrument of that will be discussed.

In this part, any instrument should meet the target specification criteria in order to be chosen:

2.1.1. Microcontroller

Perhaps one of the most important issues of the growing technology in these days is how to increase the speed of the processor meanwhile optimizing the consumption energy or in other words decreasing that is becoming a critical issue. So choosing the microprocessor for any product is not a matter of speed anymore but it's the compromising between power, speed and price of them.

The MSP430F2122 [14] from T.I Company [5] has been chosen because of its ultra low power consumption, feasible price, and suitable speed. Below some specification about this microcontroller are listed.

After reviewing "performance per Watt" and "Performance per Watt per Dollar" charts. Obviously MSP430 is the best choice right now for our transmitter device but there are some additional advantages which are listed below:

  • Proper data sheet: everything can be found over TI data sheet.
  • Easy to programming in compare with others. With the kit several sample code is provided. Also GCC (GNU Compiler Collection) which is free of charge is supported.

NOTE: Current version (3.2.3) of GCC compiler for MSP430 processors, include full set of header files. In this stable version all the data types except floating numbers with double precision are supported. Also during installation it's necessary to download some sort of patches from GNU website.

2.1.2. GPS Module

Another device which is used in the transmitter part is the Fastrax IT321 [7] GPS module in order to send the exact coordinate of the sink person. The module specification has been shown in the Table3.

Some advantages of this module are:

  • The size of this module is 10.4mm (Width) * 14.0mm (length)* 2.3mm (Height), so enable designers to have slim PCB.
  • NMEA (The National Marine Electronics Association) and Sirf Binary protocols are both supported. In the following chapter a brief explanation and differences of these protocols will be given.
  • Serial interface speed can be set up to 115200 bps.
  • A part of board acting as the antenna so there is no need for soldiering extra wires or etc.

2.1.3. Radio

The radio chip which is in used in this device "ADF7021" [8] is a high performance, low power, low cost, and highly integrated transceiver with the high working frequency range. The specification of this chip which is described in Table 4(Transmitter part) and Table8 (Receiver part) made that somehow unique in the market. "The ADF7021 is the only IC that meets the strict FCC Part 90 regulatory standard. In addition, it has excellent radio performance with best-in-class receiver sensitivity6 dB better than the nearest competitorwhich translates into longer range," [13]. Various of modulation schemes are supported (FSK,2FSk,4FSK,MSK and GFSK) also the frequency agile PLL allows the chip to be used in frequency hopping systems.

2.2 Receiver

Many tasks had been left for receiver due to limitation of power and speed in the transmitter part.

2.2.1. Microcontroller

Like section 2.1.1 with respect to goals of the device and by comparing some common products in the market, the target microcontroller will be recognized.

2.2.2. Compass

There are many compass module in the market but what make are choice narrower is the need of tilt compensated compass sensor for this purpose. We found 2 perfect matches for using in this device one of them was HMC1055 [11] while the other one which have been chosen is Yas529 [12] from Yamaha Company. The features of this sensor are listed in the following table (Table2.7).

Also there are some features which make YAS529 unique:

  • The world smallest three-axis geomagnetic sensor.
  • The price which is less than over hundred times from other competitors.

2.2.3. Radio

The chip which is in used in this part is same as transmitter part but the receiver specifications are described in the following table:

3. Software Overview

This section will try to clarify the problem and find a simple solution for both sides of apparatus. Another aim is to inspire the ways that we can combine those hardware (which are explained in previous section) in order to get the desired functionality.

3.1 Transmitter

Figure 3.1 illustrates the overview of the transmitter device. First of all it is getting ON manually or by sensing humidity then until it finds a satellite and a validated coordination point sends the device ID and time since the device turned ON, once it finds more than 4 GPS satellite the message will be updated by coordination points of the device. In the following sections functionality of each IC and its dependencies with other ICs will be discussed.

3.1.1 Sensing humidity

3.1.2 Retrieve and calculate Device Coordination

There are two standard protocols available in the Fastrax IT321 module NMEA [15] and Sirf binary protocol [16] after handling NMEA message we found out, Binary protocol is much faster mainly because of the type of message that can be retrieved. While latitude and longitude in NMEA message need about 20 bytes of memory, Sirf binary needs 8 signed bytes in the memory. Furthermore by using NMEA data should be transformed from byte to integer while in the Sirf binary protocol just shifting the data is sufficient.

So we decided to use Sirf binary protocol in this project. To use this protocol, USART (Appendix A) port of MSP430 should be initialized properly. The setting of the processor is as follows

  • Word length : 8bits
  • Stop bit: 1bit
  • Parity bit: NO
  • Hardware Flow Control: NO
  • Baud rate: 4800bps

The module is in the NMEA mode as default, we have to send PSRF 100 input command of NMEA message in order to change to Sirf binary protocol mode. Command syntax followed by command description is written below.

End of message termination

In order to provide better understanding and brighter image of the work that has been done in this section it is good to get familiar with structure of SirfBinary protocol message. Each message contains five parts as it's depicted below:

At first it was decided to set mode parameter to zero and a specific update rate (5 second) an interrupt generates in order to retrieve the desired data but as we progressed, it has been realized that there will be an interference between radio job and USART interrupt (there should be no interrupt while radio tries to send the message) so mode 1(poll one message instantly) used for this purpose with the message id of 144. Message number 144 used because this message contains the latitude, longitude and number of satellites in range. The input message is

The message length of the output message 144 is 91 bytes. But as we just need three parameters from this message every time we only read up to byte 32, if the calculated checksum value is equal to message checksum value, after preparing them into a long value (32 bits signed value) they should be transformed to radian by this formula:

Angle in radians = angle in degrees * Pi / 180

3.1.3 Sending message via radio to receiver side

Sending data via radio has 2 main parts: turning on the radio and registers initialization, sending packet and turning off. Each of these steps will be discussed in the following sections.

Turning on the radio and registers initialization

By changing the state of the CE pin of the ADF7021 radio to one the whole chip will be enabled and ready to work. For the purpose of enhance the effective range of the radio; an amplifier is used beside the radio chip which should be turned on after 500 microseconds.

In order to configure ADF7021 we are dealing with 16, 32 bit registers. First 4 LSB (Least Significant Bit) of each registers are dedicated for the register addresses. The model of reading and writing to the register which is a bit complicated has been explained in Appendix C.

Sending packet and turning off

In order to operate packet transmission properly, we need to managing data by defining a packet structure. The criteria that should be concerned for this purpose are:

  • Due to the lots of energy that radio chip consumes in compare with other chips in our board, our packet should be as short as possible because when longer data packet means the longer time that radio is on which result in consuming more power.
  • On the other hand packet should contain all the essential information in addition to the information that makes the packet unique.

But before sending each packet, 40 bits of preamble and 2 bytes of start of frame (0x1906) will be sent. As the names indicates device ID is a unique ID which attach to the MOB device during the production process. The second part of messages has 16 bits which first 12 bit from left indicates the number of minutes since the MOB is activated or in other word time in water. Next 3 bits belong to kind of the message. Right now in this version we have only one kind of message so these 3 bits are constants and fixed to be 6 and the last bit is indicating that whether MOB has access to the valid satellites or no or in the other word it means that the data that going to be sent are updated or no. if this bit set to one it means that device has a clear view to the GPS satellites and if its set to zero it means there is not. The next piece of the message contains the latitude and longitude that was calculated before when the GPS module retrieves the data from the satellites but as it takes about 3 minutes in order two find the satellites and receive the validated data the default value for these two byte are 0xFFFF which will not coordinate anywhere in the earth. Last 16 bits are the CRC16 (information about CRC16 can be found in Appendix D).

3.1.4 Timer

Because of following reasons, timer is essential for this project:

  1. In order to save as much as power, each time after sending the packets all the components in the device goes in standby mode for the specific amount of time.
  2. As it was mentioned previously, since the device gets activated the time in the scale of minutes should be send to the receiver side continuously.

For these purpose internal timer of MSP4302122 in up mode has been used, as figure 3.3 shows in this mode counter increments from zero to the desired value which can be set in the TACCR0 register repeatedly , when it reaches to the this value an interrupt will be generated and the counter value restarts automatically. We decided to get interrupt in each 10 milliseconds, because this version of project runs under speeds of 1 MHz every 10000 clock cycle will be 10 milliseconds so the TACCR0 register value should be set to 10000. So each hundred times (1 minute) the times in water value increments by 1.

But for leaving the device in standby mode we need to stop the processor in the specific amount of time. MSP430 processor has 5 modes except active mode which everything is active, 4 low power modes exist. Because the internal clock of msp430 (SMCLK) is used in this project we had to choose a low power mode which internal DCO and SMCLK being active always even in standby mode. Table 3.5 shows the different functions of operation modes of processor.

By having a look to the table 3.5 it will be obvious that the right choice is Low Power Mode 0 (LPM0) because that's the only mode which both SMCLK and DCO are active at the same time.

1. Bibliography

1. ELT. s.l.:, 2009.

2. ACR's Mini B 300 ILS H2ON. s.l.:, 2009.

3. Alert 2 Man-Overboard Alarm. s.l.:, 2009.

4. Life Tag Wireless Man Overboard Monitoring. s.l.:, 2009.

5. Atmel. [Online] [Cited: November 28, 2009.]

6. Microchip. [Online] [Cited: November 28, 2009.]

7. Fastrax IT321 GPS. s.l.:

8. ADF7021. s.l.:

9. STMicroelectronics. [Online] [Cited: November 28, 2009.]

10. MAXIM. [Online] [Cited: November 28, 2009.]

11. Honeywell. [Online] [Cited: November 2009, 28.]

12. YAS529. s.l.:

13. Scouras, Ismini. Narrowband RF chip delivers high receiver sensitivity. [Online] eeProductCenter, October 10, 2006. [Cited: November 29, 2009.]

14. TI. [Online] Texas Instruments, 1 3, 2010.

15. NMEA Refrence Manual. [Online] 2009.

16. Sirf Binary Protocol Refrence Manual. [Online] 2009.

17. MSP430, User Guide. [Online]

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