16 SAIL Instrument 1
Hardware
Our first target will be to match and extend the capabilities of the popular Velocitek ProStart instrument for sportboats and skiffs.
It’s only fitting to protect it from the elements in an old case from an earlier commercial instrument.
The first prototype was assembled on a solderless breadboard as a proof of concept, however the connections were unreliable in a marine environment, especially if the system was exposed to spray. This version includes a feather processor module on the left and an instrumentation module on the right, along with a battery. Separating the instrument system from the processor provides the option of exploring performance capabilities of different processors. The initial combination includes:
- Feather M0 WiFi combined with an OLED display and a real time clock (RTC) module that includes a microSD slot.
- GPS module communicating via serial NMEA sentences
- Bosch BNO055 integrated Inertial Measurement Unit (IMU) connecting via I2C
- BME280 Environmental Sensor provides temperature, humidity and barometric pressure via I2C
- 2500 mAh LiPo Battery connected to the Feather for seamless USB interaction and charging
Note that the trace for the wake pin on the M0 WiFi was cut on the underlying prototyping wing to allow the cable harness connection to include a ground pin.
Timing Considerations
There are multiple sources for time of day. The WiFi can provide NTP time if there’s a connection. The GPS provides time of day, but may be a little off due to the latency of the serial communication, and some jitter has been seen at the fractions of a second level. The RTC needs an initialization source from somewhere to re-sync. The millis() clock gives a long time base that increases monotonically and has very little latency.
We don’t want the time base to shift in the middle of a measurement.
Media Attributions
- Outside Sail 1 Instrument © Rick Sellens is licensed under a CC BY (Attribution) license
- Inside SAIL 1 Instrument © Rick Sellens is licensed under a CC BY (Attribution) license