Modern sail boat transducer and chartplotter systems offer advanced features which show optimal tacks and laylines to allow the most efficient and fast routing to the destination to be easily determined. My project aimed to recreate this functionality without the many thousands of pounds required for a chartplotter with this functionality and the new compatible instrument transducers to feed it with the boat performance information.

Recent plugin developments in the open source PC based navigation software OpenCPN, meant that this functionality was now within reach, my challenge was to get the data from a variety of legacy transducers into the PC system to allow the calculations to take place.

The boat had three instrument data feeds of interest:

• An AutoHelm Log
• NASA Marine masthead anemometer
• NASA Marine depth gauge

The challenge was to get the data from these disparate legacy systems onto a wireless Panasonic Tablet running the OpenCPN software.

The initial system design was based around two main components. A pyboard interfacing with all the instruments through various circuitry sending NMEA0183 output via UART to a Raspberry Pi, which was acting as a boat WiFi Hub and serving the NMEA data via tcp to the OPenCPN.

In addition to the on board existing instruments, the pyboard circuitry also included a 9DOF compass, accelerometer, gyroscope unit and the RPi had a GPS puck to provide the final pieces of information to allow the tactics plugin of OpenCPN to run.

However, this system was found to fail as the I2C signals from the NASA Marine instruments (these will be discussed in detail in a future log) were not able to be transferred the length of the boat on wires to the pyboard. To overcome this limitation I had two options, to use circuits based on a P82B96P to boost the signal to allow its transfer over the required distance or to switch to using local ESP8266 modules to decode the signal and then to transfer to the RPi over wifi.

Whilst signal boosting was perhaps the most straightforward approach I opted for the latter approach which gave rise to this project.