Hardware Features
The core requirements for a bathymetric data logger are that it needs to interface to the known data buses generally available on ships; that it has some mechanism to store the data between transmission events; and that it has some mechanism to transfer the stored data to the outside world. In most vessels of opportunity, these interfaces follow the NMEA0183 standard (essentially specially formatted ASCII serial messages using RS-422 differential serial as the physical layer), or the NMEA2000 standard (binary formatted messages using a custom variant of CAN bus as the physical layer). Since WIBL will have to deployed on ships where the bus is not known in advance, both networks have to be supported. Finally, in addition to the physical interfaces, some control logic is required to sequence events; a microcontroller is now normal in this role.
The core requirements for the system are therefore:
- A microcontroller to sequence operations.
- An SD card to store the captured data.
- A CAN bus controller to talk to the NMEA2000 bus.
- A CAN bus transceiver to provide the physical layer interface to the NMEA2000 bus.
- An RS-422 transceiver and opto-isolators to provide the physical layer interface to the NMEA0183 bus.
- A wireless interface for communication with the logger, and transfer of data.
These requirements are relatively simple to achieve, and the parts required are commonly used in both the instrumentation and automotive worlds, making them (usually) available in volume and cheaply. This ensures that the total cost to manufacture a logger of this type can be minimized.
Hardware Implementations
Since the requirements for a WIBL-style logger are relatively limited, there are a number of potential implementations of the system. The initial development was conducted with a breadboard and development sub-modules; the first custom implementation used a PCB to host development modules; and the current "standard" implementation uses a full custom PCB based around the Espressif ESP32 microcontroller with primarily surface-mounted components (this aids in manufacturing, and reduces costs of production).
Further details of the hardware implementation can be found in the Wiki associated with the project. The design files for the custom hardware (schematic and PCB layout) are provided in the repository, and a snapshot of these, plus the design files (Gerbers for the PCB, pick and place information, and the bill of materials) in a format suitable for submission to a fab are archived for further download. The STL files for the 3D-printable enclosure are also part of the archive.
Installation and Documentation
WIBL loggers are being used by COMIT at the University of South Florida for their Crowd the Bay project. As part of this, they have prepared information on installing the loggers, and forms to assist in capturing the installation information. The details can be found here.