This repository holds firmware for the SparkFun OpenLog specifically tailored to logging measurements from the Sea-Bird SBE 49 FastCAT CTD on the Inkfish Open Oceans landers.

The SBE 49 is capable of sampling at 16 Hz, but the lander controller functions best when it receives CTD data at 1 Hz. This firmware logs at the higher rate, then downsamples the data and passes it to the controller at the lower rate.

(NEW): The hardware directory contains KiCad designs for a printed circuit board that accepts a wider input voltage range and is designed to be significantly more resilient to power surges.

The only components needed are the SparkFun OpenLog and a MAX3232 transceiver breakout.

(Note that some components are represented as SIP ICs for purposes of illustration. The leftmost pin of the MAX3232 transceiver above is T1OUT.)

In summary, the circuit interposes the communication between the CTD and Lander Control Board:

 -------            ---------------           ----------- 
| CTD   |          | MAX3232       |         | OpenLog   |
|       |          |               |         |           |
|   TX -------------> R1IN  R1OUT ------------> RX       |
|       |  RS-232  |               |   TTL   |           |
|       |     ------- T1OUT  T1IN <------------ TX       |
|       |    |     |               |         |           |
 -------     |      ---------------           ----------- 
             |
             |      ------------------------------------- 
             |     | LCB                                 |
             |     |                                     |
              ------> CTD_RX                             |
                   |                                     |
                    ------------------------------------- 

Note: Consider the need to attach the programmer to the OpenLog. See Programming section below.

This project uses PlatformIO. You can build the firmware and program the OpenLog using the PlatformIO Core CLI tool.

First, clone the repository with submodules:

git submodule update --init

Patch SerialPort.h to disable BUFFERED_TX and ENABLE_RX_ERROR_CHECKING:

sed -i.bak \
  -e 's/\(#define BUFFERED_TX\) 1/\1 0/' \
  -e 's/\(#define ENABLE_RX_ERROR_CHECKING\) 1/\1 0/' \
  Libraries/SerialPort/SerialPort/SerialPort.h

Compile the project using PlatformIO to check for errors:

pio run

The OpenLog can be programmed using a 4-wire TTL UART to USB adapter. Review the OpenLog Hookup Guide for details on wiring. Importantly, the OpenLog DTR pin (inexplicably labeled GRN) must be connected to the programmer's DTR or RTS output.

pio run -t upload

A USB to RS-232 cable (DB-9 connector) can also be used for programming. The RX/TX pinout on the DB-9 connector must be confirmed due to the various permutations.

The Bus Pirate can be used as a programmer. Attach the pins as follows:

Place the Bus Pirate into the transparent UART bridge mode with flow control signaling:

# Enter UART mode, use baud 115200 for programming
HiZ>m
2. UART
(1)>2
...

# Enable power output on the pins
UART>W
POWER SUPPLIES ON
Clutch engaged!!!

# Start the transparent bridge
UART>(3)
UART bridge
Reset to exit
Are you sure? y

Disconnect the terminal session and proceed with programming the board.

By default, the OpenLog expects to receive and transmit data at 9600 baud, the same rate as the Lander Control Board. If this needs to be changed, a different baud rate can be written to the file config.txt at the root of the microSD card.

The SBE 49 must be configured for OUTPUTFORMAT=3, engineering units in decimal.

A quick and dirty test script can be used to send fake samples to the logger from a PC. The script counts the number of downsampled replies that match expected values.

python3 test/simctd.py --sal --sv /dev/tty.usbserial

The --sal and --sv flags simulate the OUTPUTSAL (salinity) and OUTPUTSV (sound velocity) options on the SBE 49.