Terminal Interface¶

Written by Grace Lo & Alina Wang

This integrated terminal interface system combines SD card functionality with motor testing and CO₂ and methane sensor measurements, displayed on a serial monitor mimicking your computer's terminal or PowerShell command-line interface. It has a series of valid commands to navigate and alter files/directories on the SD card, as well as change the motor or data logging settings of the system. Like the flux_chamber.c system, it can also collect environmental data from both the Sensirion SCD30 (CO₂, temperature, humidity) and the Figaro NGM2611-E13 (methane), and write this data with timestamps to a .csv file.

All base motor, SD card and sensor functionality is handled by their respective libraries, documented on the Stepper Motor, CO₂ Sensor, Methane Sensor and SD Card pages. The intent of this document is to show how these modules are integrated with a command-line interface for testing specific setting changes without the need to compile the code and reflash the Pico. As such, this page will often refer to Flux Chamber for various steps and mainly highlight the differences.

Pin Connections¶

Breadboarding best practices should be followed. Use the shortest possible wires for maximum clock speed, which when using solderless protoboards is capped at ~20MHz due to pin capacitance. The pin connection for each components is already documented on their respective pages and the integrated version simply connects all the components together.

Pin Connections

API¶

The serial monitor can be connected using the Raspberry Pi Debug Probe or the Adafruit #954 USB to TTL Serial cable, both of which can be connected via:

  • RX → UART0_TX (gpio 0)
  • TX → UART0_RX (gpio 1)
  • GND → GND

When the system resets, the driver prints SD card information to the serial terminal. Then you can issue the following commands:

  • runmotor <direction> <steps>: run the motor up/down for a certain number of steps
  • setdate <yyyy-mm-dd> <hh:mm:ss>: set the RTC intialization of date/time
  • setper <period>: set the data logging period in ms (default set to 5 seconds)
  • write <filename>: write data logging to a file
  • print <filename>: print the content of the filename
  • rm <filename>: delinks (deletes) a file
  • ls <directory>: lists directory contents; default is current directory
  • cd <directory>: changes current directory
  • mkdir <directory>: new directory
  • help: prints all valid commands

Code¶

All code is in the CornellFluxChamber Github repository. The file terminal_interface.c contains all core logic for sensor initialization, data logging, and command-line interactions. The code is organized in protothreads for modularity. Protothreads are extremely lightweight, stackless threads designed for memory-constrained systems; the library is written entirely as C macros by Adam Dunkels.

Includes¶

The first lines of code in the C source file include header files. Don't forget to link these in the CMakeLists.txt file! All of the header files are the same as flux_chamber.c, except for the pico/sleep.h library that is not necessary for this implementation.

main()¶

Refer to flux_chamber.c for the core allocation and protohread setup prcoedures.

Protothread¶

Initializations¶

The protothread begins with variable declarations for processing serial input (cmd, arg1, arg2, arg3, token), date/time (datetime_buf, datetime_str), and frequency (logging_frequency_ms). In addition, the datetime_t struct is initialized to a default Sunday 01 January 00:00:00 2000 and the logging frequency is initialized to a default 5000 ms (or 5 seconds).

Then the SD card, CO₂ sensor, and ADC for the methane sensor are initialized in the same way as flux_chamber.c.

Serial Terminal¶

The serial terminal runs indefinitely when the RP2040 is powered on. At the start of each loop, it waits for user input, then tokenizes cmd arg1 arg2 arg3. Each of the commands are checked in sequential if-statements and are described below:

The setdate command uses arg1 and arg2 to set the date and time, respectively. The date is tokenized by delimiter - and the time is tokenized by delimiter :. The fields for the datetime_t struct are updated accordingly and reinitialized in the real time clock.

The setper command uses arg1 to set the period (in ms) for data logging. When the write command is issued, the period is used to put the system to sleep in between data logging entries.

The write command uses arg1 as the filename to write to. If the file does not exist, a new one will be created. If the file already exists, new data will be appended to the file. The contents of the file are divided into two sections - header and data. The header includes the Pico ID so that each system can be identified uniquely when many flux chambers are deployed. It also defines each of the columns. At present, the columns are DATETIME, TEMP, HUM, CO2, CH4. Then the data is continuously written in a loop. As mentioned previously, the logging period is used to specify the sleep time between data logging entries.

The rm command uses arg1 to define the file path for removing the file.

The ls command can be used with or without arg1. ls alone will print all items in the current directory and ls arg1 will print all items in the arg1 directory.

The cd command uses arg1 to define the file path to navigate to.

The mkdir command uses arg1 to name the new directory that will be created in the current directory.

An example of setdate, setfreq, write, and print used in the serial terminal and the corresponding CSV file is provided below:

Serial Terminal CSV File