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BoatDetect

a low-cost, boat traffic data logger

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BoatDetect detects and logs boat traffic in marine and freshwater environments. It can be used to monitor boat activity in marine protected areas, waterways, and high risk aquatic ecosystems. Once collected, the data is analyzed to understand hourly, daily, and weekly boat traffic trends. The trend information can better inform when and where to place enforcement resources or can show how changes in boat activity levels correlate to other changes in an underwater ecosystem.

The Problem

The high cost of current boat traffic monitoring systems has prevented widespread adoption of the technology. Without these monitoring systems, ecological damage from unrestricted boat activity and encroachment on marine protected areas goes undetected. 

"Protected areas in the ocean, unlike a forest patch, are far more difficult to manage and face increasing challenges, especially as they expand to enforce boundaries and policies with no observable boundaries and or protective barriers to the sea" (Conservation X Labs Open Challenge, Hackaday Prize 2020).

The Solution
A low cost, reliable product that agencies and individuals can use to monitor boat activity in marine and freshwater environments. Then use the data collected to develop protection strategies or to understand how boat activity levels trend with other changes in an aquatic ecosystem.

Product Design Requirements

  • less than $40 in material costs
  • assemble in less than two hours
  • at least four weeks of continuous operation between battery charges
  • tamper proof
  • low ecological impact of installation
  • detect boat traffic within a 4m or greater radius from the device

Development Stages

  1. System architecture development and cost study - complete 06/21/2020
  2. Piezo microphone boat detection proof-of-concept
  3. Breadboard prototype
  4. Field ready prototype
  5. Prototype field testing

  • Boat Detection Systems

    John Opsahl3 days ago 0 comments

    A common method for vessel detection (primarily for collision avoidance) in the marine industry continues to be AIS (automatic identification system) in combination with radar. As part of AIS, each vessel transmits position, course, speed, and a unique signature that is received by other nearby vessels. As you can imagine, these systems are very accurate but also very expensive.

    Hydrophone arrays and advanced camera systems are some of the lower resolution solutions available for detecting and tracking boat traffic from a single vantage point in areas like bays and waterways. Both are still relatively expensive, require a significant amount of data processing and consume enough power to require an expensive solar energy/battery system.

    The BoatDetect device delivers a low power boat detection method at a fraction of the cost of existing systems. The caveat being that the BoatDetect device only has the resolution of detecting whether or not a vessel is in the vicinity. Even so, this level of resolution can still be useful to conservation groups and individuals who operate under a limited budget. 

  • New Enclosure Design

    John Opsahl6 days ago 0 comments

    I have transitioned to a PVC pipe fitting enclosure for the BoatDetect device. The previous enclosure, a 1000ml wide mouth water bottle, did not have a flat surface to mount the piezo diaphragm to. I considered pouring a small amount of epoxy resin in the bottom of the 1000ml water bottle to create a flat surface, but decided against it because of the added cost and hassle of working with epoxy. At $9.60, the PVC enclosure is only $3 more expensive than the 1000ml water bottle. It makes up for the added cost with a wider access port and is potentially easier to source than the bottle. The wider access port allows a little more space for the electronics assembly and certainly will make it easier to access the batteries and SD card. 

    I superglued the piezo diaphram to the inside surface of the bottom plug. It did take me a while to find a PVC fitting that had a flat surface to mount the piezo to. When I get around to developing a build-it-yourself guide, I will recommend that builders start by finding a PVC fitting with the flat surface and build up the rest of the enclosure around that fitting as I have done here. 

    I have some reservations whether the DWV (drain, waste, vent) threaded connection will be be able to hold pressure at depth. As the name "DWV" implies, they are not used for high pressure PVC installations. On top of that, the threaded connection would also likely require that a thread sealant be applied and inspected every time the device is opened up. The alternative is a wingnut compression pipe plug which does have some design history with other DIY underwater enclosures. I just checked price and looks like the compression pipe plug is actually a little cheaper than the combined price of both the DWV threaded plug and threaded spigot fittings. It would require a small length of PVC pipe to fit in but that ought to be cheap. Well then, the compression pipe plug is roughly equivalent on cost and a clear winner on both pressure rating and ease of installation/removal. I will buy the small section of pipe needed this week and get the enclosure glued together for testing.

  • Breadboard Data Logger Prototype

    John Opsahl06/28/2020 at 21:45 0 comments

    I completed a BoatDetect breadboard data logger prototype with all the major functional features. It includes a real-time clock module, SD card module, and an Arduino Nano. 

    At a high level, the system repeats this sequence of events during operation:

    1. the Nano enters sleep mode
    2. the real-time clock module wakes up the Nano after a configurable amount of time
    3. the Nano reads an analog input pin
    4. the Nano writes the timestamp and analog input value to a file on the SD card
    5. repeat steps 1 to 4

    The sleep/wake up strategy reduces the power consumed by the Nano. 

    I plan to implement a few more power reduction strategies in the coming weeks:

    • add a transistor on the SD card power, only power the SD card when needed
    • accumulate logged timestamps and analog input data in SRAM, write this data to the SD card all at once (reduces the amount of time that the SD card is powered)
    • remove the power LED from the Arduino
    • remove the voltage regulator on the Arduino and replace it with a regulator that is more efficient at lower currents
    • remove the power LED from the real-time clock module

    Overall, I am very pleased with how this prototype operates and excited by it's simplicity. I was able to get everything wired and working in a little over three hours. I leaned heavily on the Arduino data logger designs that others have posted online.

  • Microphone Circuit, First Iteration

    John Opsahl06/14/2020 at 19:34 0 comments

    The first iteration of the piezo diaphragm microphone circuit includes:

    • piezo diaphragm used as a microphone (represented as the AC source and 15nF capacitor)
    • high pass filter with 250Hz cutoff
    • 40dB amplifier
    • low pass filter with 1kHz cutoff
    • half-wave rectifier with a smoothing capacitor

    The microcontroller will wake up at 2-4 second intervals, measure voltage at the rectifier, and write the analog voltage reading and RTC timestamp to the SD card. 

    Parts are on order and should arrive in 30 to 50 days.

  • System Architecture, Second Iteration

    John Opsahl06/13/2020 at 16:55 0 comments

    After several hours of internet research I have been able to reduce the total material cost of the BoatDetect system from $37 to $24 ! The resources available online for developing a low-cost, low power Arduino data logger are just fantastic. This device may be my own design but it is certainly built on the shoulders of hackers across the internet that have shared their knowledge freely.

    The most significant changes are:

    • switch from a Arduino Nano to an Arduino Pro Mini 3.3V for reduced power consumption
    • reduce micro SD card storage size from 4GB to 128MB for reduced cost and potential for reduced power consumption
    • Tiny85 microcontroller no longer needed because of low operating current of Arduino Pro Mini
    • reduce the number of 3400mAh 18650s needed from four to two and still be able to operate for four weeks
    • removed 3D printed components to reduce cost and avoid need for access to a 3D printer

  • Most Parts on Order, Piezo Diaphragms Received

    John Opsahl06/07/2020 at 15:45 0 comments

    Most of the parts are on order from Aliexpress and should arrive in 30 to 50 days. In the meantime, I will be developing and testing the active band pass filter and envelope detector circuits. I also received ten 35mm piezo diaphragms this week. I will be using them to create several DIY hydrophones so I can start taking underwater audio recordings of boats.  

  • System Architecture, First Iteration

    John Opsahl06/01/2020 at 02:43 0 comments

    The first iteration of the BoatDetect system architecture is complete. The device is mounted underwater and tethered to the bottom. A piezoelectric diaphragm senses the noise generated by boats passing by overhead. An active low pass filter removes all frequencies above 1000Hz and amplifies the signal. An envelope detector outputs a positive peak amplitude signal. The Tiny85 microcontroller periodically reads the analog signal. If the voltage of the signal is above the detection threshold, the Tiny85 wakes up the Arduino Nano. The Nano writes a timestamp to a file on the SD card and goes back into power down mode. The Tiny85 continues to wake up the Nano every time the voltage signal is above the detection threshold. The Tiny85 stops waking up the Nano after about four weeks when the battery state of charge drops below 10%. At this point, the device has to be retrieved for service. The data file is downloaded from the SD card and the batteries are removed and replaced with a fully charged set. A quick analysis of the data will show hours of the day and days of the week when boat traffic is heaviest in the vicinity of the device.

    Total estimated cost of the system is approximately $37. The cost breakdown by component is detailed in pie chart below. Almost 50% of the cost is in the batteries and water bottle.

  • Low-cost Hydrophone

    John Opsahl05/28/2020 at 05:11 0 comments

    The first challenge of this project is development of a low cost hydrophone. Fortunately most of the legwork has already been done for me. Governments have funded research on vessel fundamental frequencies, weekend hackers have developed and tested several DIY piezio diaphragm hydrophone designs, and a couple researchers even developed a frequency response curve for a common DIY hydrophone build. 

    According to a paper titled "Acoustic surveillance of small surface vessels in confined areas" by A. Tesei et. al of the NATO Undersea Research Center in Italy, the fundamental frequency and source level of 7m outboard motor and fishing boats range from 0.25 to 1 kHz and 150 to 156 dB re 1uPa @ 1m respectively. 

    You can find dozens of DIY piezio diaphragm hydrophone builds online, but this one , do-it-yourself hydrophones, by John Grzinich in Istanbul even includes a sound recording of motor boats. 

    Over to the west side of the Atlantic, two researchers Eduardo Vivas and Braulio Lopez submitted a paper titled "Construction, calibration, and field test of a home-made, low-cost hydrophone for cetacean acoustic research." to the Acoustical Society of America. The paper details a frequency response curve of a DIY hydrophone. The frequency response curve starts from -55 dB re 1 V/uPa near 600Hz and continues upward to -25 db re 1 V/uPa at 8kHz. So capturing lower frequencies down to 250 Hz that are characteristic of fishing boats may be a challenge, but otherwise its still worth getting some parts on order and building one myself to test.

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Discussions

Paul Breed wrote 06/15/2020 at 00:43 point

Find some electrically insulating oil or other non-conductive, non-compressable fluid.

Fill your plastic water bottle with this fluid.... 

Use a normal mems microphone...

Fluid will keep plastic water bottle from being crushed.

Fluid will also conduct sound to microphone....

Not sure if it will work, but its an idea...

  Are you sure? yes | no

John Opsahl wrote 06/15/2020 at 01:54 point

Thanks Paul. I have been thinking about sectioning off the bottom of the water bottle and filling it with a non-conductive liquid like mineral oil for the microphone as you suggest. Hadn't considered a MEMS microphone yet. Thanks for that. Enjoyed reading up those. The current approach is to super glue a piezo diaphragm to the bottom of the water bottle. 

With the current design I am relying on air in the bottle to provide some bouyancy. Hadn't put too much thought yet into how much external water preasure a cheap water bottle can withstand. Sounds like a fun experiment.

  Are you sure? yes | no

CNLohr wrote 05/28/2020 at 06:27 point

That makes sense.  No need for real time feedback if the policy doesn't get updated in real time anyway.

  Are you sure? yes | no

CNLohr wrote 05/28/2020 at 05:03 point

How do you plan to communicate the current boat traffic information back?

  Are you sure? yes | no

John Opsahl wrote 05/28/2020 at 05:25 point

I am targeting a low tech solution so the current architecture is that the device stores all the data. Then users will collect the data from it when they physically retrieve it at every battery recharge interval. The boat monitoring isn't real-time but the information can still be used to inform when the majority of boat traffic is occurring and for how long. Knowing this can help conservation or enforcement agencies know where and when to position resources to be the most effective.

  Are you sure? yes | no

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