As soon as the logger is powered on, it is operational, and will log any incoming data to the USB stick. On power on it creates a new log file, and writes to this until either logging is stopped and restarted by the button, or power is switched off and on again. Log files have the extension .TSV, and just contain standard NMEA sentences, exactly as received.
The logger takes data from both input ports, and as soon as a sentence is complete from one port it is written to the file on the USB stick. Incoming sentences have basic validation for the beginning $ and ending <CR><LF>, overall sentence length, a valid checksum (when present), and also a timeout.Seatalk data packets also have basic validation, and are then encapsulated within a proprietary NMEA sentence - the logger does not do any translation to NMEA sentences. The logger does not validate the content of either NMEA or Seatalk sentences, which ensures that all data is logged.
The device requires 9-30V DC, and a solid green power light indicates good power. A rapidly flashing light indicates a voltage below 9V. No power light indicates no power, a very low voltage, or reverse polarity. The device is designed so that when the power supply is switched off, there is enough power available to write any buffered data to the USB stick, so no data is lost, and the USB stick is not corrupted by losing power part way through a write operation.
Inputs are received and buffered on both ports. When a complete NMEA sentence or (with the Seatalk option) Seatalk data packet is received, it is validated, e.g. for NMEA the beginning $ and terminating <CR><LF> are checked, as well as the sentence length and checksum (if present), and there is also a timeout. Valid NMEA sentences are sent immediately to the USB port, and the LED for that channel flashes green. Invalid NMEA sentences are discarded, and the LED flashes red. For Seatalk, the same process is followed except the Seatalk data packet in this format:
where aaaaaa is the Seatalk data packet, and cc is the standard NMEA checksum.
The logger is generally supplied with a USB stick, but will work with any Type 2 (or higher) USB stick that has been formatted as FAT or FAT32 - FAT32 is recommended. Other formats such as ExFAT or NTFS are not supported, nor are other USB devices such as hard disks with a USB interface, nor is the use of a USB hub. If the USB device is not recognised, the USB LED will flash as per the table below.
A USB stick can be inserted at any time, and data will be logged to it immediately. To remove a USB stick, it is important to ensure that this does not happen during a write operation, as this risks not only losing that data, but also corrupting the entire contents of the USB stick. Either power off first, or press the button beside the USB port to switch off logging, remove the USB stick, and then press the button on again when you want to resume logging.
A new log file is created either by switching power off and then on, or by pressing the USB switch once to stop logging and then again to start logging. This allows logging to occur just as times of interest to the user, or to take a snapshot of NMEA data coming off the instruments.
The logger does not have its own clock, so all files will appear with the same date/time stamp. Where time stamped data is needed, this is best obtained from logged GPS data, e.g. in the ZDA or RMC sentences. File names are in the format nnnnnnnn.TSV, where nnnnnnnn is a number with leading 0's. In general, files are created sequentially, but this cannot be guaranteed, e.g. if there is already a file of that name it will leave it and move on to the next one.
In general thew USB LED will show solid green when a USB stick is inserted, occasionally flashing red when data is written to memory. In the event of an error condition, this is shown by the following red flashing groups.