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AIS Alarm - Prototype Hardware

fmilburn

Project Objective: Develop an open source AIS Alarm that alerts sailors that a new marine vessel with AIS is within range

 

In this post I will describe the hardware to be used for prototyping and why it was chosen.

image

Starting in the upper left and going counter clockwise:

  1. dAISy Single Channel AIS Receiver - This receiver is inexpensive, reliable, and I have experience with it.  It is open source and the developer is open to working with hobbyists on their projects.  The antenna is not shown but I can connect to it in my work area and pick up AIS signals.
  2. LM1117-3.3 and 0805 SMD 10 uF tantalum capacitors - I may or may not use a LDO in the prototype but it will be required in the final design.  A LDO makes sense when using a radio due to low noise and efficiency is not an overriding concern here.  I happen to have these on hand and have used them in the past.  I will follow the datasheet for the design which recommends 10 uF tantalum capacitors.  The SOT-223-4 and 0805 can be hand soldered and I have adapters for 0.1" connection if needed.
  3. MSP-EXP430F5529 - Almost any LaunchPad for the MSP430 series will do.  Another good choice would be the new MSP-EXP430FR2433.  It could even be used for the prototyping since it has FRAM and would be easy to port to another part in the FR2xx series.
  4. Breadboard
  5. Piezo-Electric Buzzer - I have a couple on hand of unknown origin.  I will use an active buzzer (one that buzzes with just voltage applied) to start due to simplicity.  When the final design is done I will select one from a known manufacturer.
  6. Small MOSFET - This will be used to supply 5V to the buzzer.  I happen to have BS170 through hole versions on hand but will select a SMD MOSFET for the final design.
  7. LEDs and resistors - I have 5 mm through hole on hand but will look for high visibility panel mount for the final design.  Resistors will be 0805.
  8. Button Switches - These are what I have on hand.  Will need 90 degree or something different for the final panel mount
  9. Slide Switch - Again, what I have on hand.  Will need something panel mounted in the final design.  May decide to add a "quiet" switch for the buzzer in the final design (feature creep already?)
  10. MSP430FR2111 - I think this will be the best MSP430 FRAM chip for this project although there are versions with increased FRAM and SRAM if needed.  FRAM is an advantage since I need to write quickly and retain the incoming AIS messages when the project is unplugged from it's power supply.  There are also sufficient GPIO, timers, and UART. I checked Newark/element14 and they weren't carrying it as I write this - I obtained my samples directly from TI.  I previously designed the little board in the photo and had it fabricated at OSH Park so I can use it on a breadboard.

 

Past Posts on this Project:

AIS Alarm

AIS Alarm - The Process

 

References and Links:

WEGMATT LLC - dAISy AIS Receiver - low cost AIS receiver

Texas Instruments MSP430FR2xx FRAM Microcontrollers - Post No. 4

  • in reply to DAB

    Great questions...

     

    AIS is transmitted as message bursts on two VHF channels:

    • Channel A 161.975 MHz
    • Channel B 162.025 MHz

     

    The messages are sent out periodically and have information such as unique vessel identification (MMSI), location, heading, speed, etc. 

     

    There are two main types of AIS transceivers used by vessels: 

    • Class A transmits at 12.5 W and is required by large commercial vessels
    • Class B transmits at 2 W and is used by smaller vessels and pleasure craft

     

    Data is sent out every 2 to 10 seconds depending on speed when underway.  Of course many smaller craft do not have AIS transceivers at all. 

     

    As expected, the primary variables in reliable reception are transmission power, antennas, height of antennas, receiver selectivity, amount of noise, etc.   The signals can be picked up in space from satellites.  I think of it as basically line of sight for my purposes though.  Class A range is often given as 20 nautical miles and Class B as 5+ nautical miles.  I am located about 100 meters up a hill and can easily see 20 nautical miles for Class A with occasional skips from much further.  On the other hand, I can't see over the hill to Elliot Bay which is only a couple of miles away.

     

    There are a number of internet sites where AIS data from around the world is collected, e.g. http://www.marinetraffic.com/

     

    This may not be too useful if you are at sea without an internet connection however :-).  In that case for small boats there is software that can be used with a receiver such as open source OpenCPN which I use.  For example, here is a typical view using OpenCPN from my location showing the type information that is available:

    image

    In this case I have clicked on the Washington State Ferry Wenatchee to get additional information in the window lower left.

     

    My project will gather the same information and store it in FRAM without need for a PC.  There is one practical use case I can imagine:

     

    • A small sail boat that wants to monitor traffic and has a low power budget - i.e. does not want to keep their computer running all the time.  When the alarm sounds they would bring up the PC and plug this device into it which would give them information on the vessel.

     

    This was suggested by another person and I am pursuing it mostly for the intellectual challenge.  It might also be useful for making an onsite log of vessels going by a location without dedicating a PC.  It is also possible to send the information to the "cloud" or a site like MarineTraffic if you have a microcontroller with an internet connection and I have done that successfully.

  • Interesting project.

     

    I am assuming that AIS equipped vessels send out a ping signal that these detectors can pick up and alert the operator that another vessel is within range?

     

    About how far away can the signal be reliably detected?

     

    DAB