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21.0 SD Card (T7 Only) [T-Series Datasheet]

SD Card Location (Case)

SD Card Location (PCB)

The T7-Pro ships with a 2GB (or larger) microSD card installed (SLC technology).  It might also be referred to as uSD, µSD, or just SD.

The T7 does not have the microSD card installed, but does have the card holder installed so a compatible microSD card can be installed in the field.

The retainer opens by sliding the metal piece forward, then lifting.

The T7 supports cards which use the SDHC standard. SDHC supports from 2 GB up to 32 GB. Larger standards such as SDUC and SDXC are not supported.

The T7 supports FAT and FAT32 file systems, but some makes and sizes behave differently.  We recommend the following SD card format:

File System: FAT
Allocation unit size: 64 kilobytes

FAT32 with an allocation unit size of 16 kB or 32 kB sometimes works, but smaller allocation sizes generally do not.  On 2 GB cards it's possible to select FAT format with a 32 kB allocation size, and that sometimes works.

Care must be taken to ensure that power is not lost during file writing or disk corruption could occur.  The rated operating temperature of the SD card is -25°C to 85°C.  For extremely low temperatures, customers can buy industrial grade SD cards, such as the AF1GUDI-OEM, from ATP Electronics, Inc.

File and directory names are limited to ASCII characters only.

The maximum number of file handles that can be open at once on a T7 is 4.  One file handle is reserved for Modbus communication to allow programs to read files off of the SD card and the remaining 3 are available for Lua Scripts.

Standalone Data Logging

The microSD card is generally only useful for people doing standalone data logging through Lua scripting, since normal T7 operation is with a host connected (so the host can store data).  Standalone logging is an advanced topic.  We provide Lua examples for logging data to the microSD, but options for retrieving the data are somewhat limited (see next section).  Standalone logging is generally limited to command-response data rates.

For information about powering the T7-Pro see the VS, Power Supply Section of this datasheet.

As an alternative to true standalone logging with the T7-Pro, consider that any LabJack combined with a host computer makes an incredibly powerful and flexible data logger.  The host computer could be a full-blown desktop machine, but could be a simple SBC (single board computer) such as Raspberry Pi, BeagleBone, or various options from Technologic Systems.

Retrieving Data from the microSD Card

It is pretty easy to write data to the microSD card in a Lua script.  At this time there are a few options for retrieving the data from the microSD:

1.  Remove (or swap) the microSD from the T7 and put it in a card reader on a computer.  On non-OEM versions of the T7/T7-Pro, the enclosure must be opened to access the microSD holder.

2.  Windows only: Use the beta SD utility for downloading files from the SD card via USB/Ethernet/WiFi.  Note that the microSD and WiFi share a serial bus inside the T7, so sometimes extra thought is required if using both at the same time.

3.  Use the registers described below to read data off the microSD.

Testing the microSD Card

Not all SD cards are compatible.  If you install a new or different SD card, we recommend the following tests to make sure it works.  If you have access to a Windows computer, we recommend downloading and running the T7uSD testing application published on the T-Series Additional Utility Applications page.

    A.  Check Kipling to make sure that the SD card is properly recognized and that the calibration status of the device is still good.

  1. Connect to the device with Kipling

  2. On the Device Info tab and make sure there is a green checkmark next to the SD Card Installed hardware option.

  3. Check to make sure the device's calibration status is still "Good".

    B. Check to make sure the SD card can be read and written.

  1. Connect to the device with Kipling.

  2. Download and run the Lua example script titled "Log voltage to file".

  3. Exit Kipling and open the SD Utility to verify that the file was written properly.

    C.  Check to make sure the T7's calibration constants can be read from the internal flash chip.

  1. If you are on a Windows computer, use LJStreamM to try streaming an analog input register from a T7.  If you get stream errors LJME_USING_DEFAULT_CALIBRATION (203) or LJME_INVALID_VALUE (1305), the microSD card being used is likely not compatible with the T7.

Errors Caused by Unsupported microSD Cards

  1. A device may get stuck in its recovery firmware version and report upgrade issues because the flash chip is not responding properly.

  2. A device may report that it is using default calibration values and it is unable to be used in stream mode. The device's calibration constants are read before streaming is started.

  3. A device may have issues when running Lua scripts that try to save data to the microSD card or errors may be reported by the SD Card utility indicating that a file can't be opened.

Accessing the microSD Card While Using WiFi

WiFi shares an internal serial bus with the SD card and Internal Flash, and at the start of joining WiFi needs about 3 seconds of uninterrupted access on this serial bus.  If a Lua script does file I/O operations during this time, then WiFi initialization will fail and the WiFi module will immediately try again.  If Lua file I/O occurs every 3 seconds or less, it is likely that WiFi will never be able to join.  A simple way to make sure WiFi can join, perhaps with a retry or two needed, is to only write every 5 seconds (or longer).

Use the following Lua pseudocode to write to a file once every 5 seconds, and read an analog input once every 500ms. See the "Log voltage to file" Lua examples in Kipling for an actual script example.

LJ.IntervalConfig(0, 500) --set the DAQ interval to 500ms, should divide evenly into file access interval

LJ.IntervalConfig(1, 5000) --set the file access interval to 5 seconds

TableSize = 5000/500

data = {}

DAQcount = 0

for i=1, TableSize do

data[i] = 0


while true do

if LJ.CheckInterval(0) then --if a data point needs to be collected

data[DAQcount] = MB.R(0, 3)--collect a new reading from AIN0

DAQcount = DAQcount + 1


if LJ.CheckInterval(1) then --file access interval complete

appendToFile(data) --save the data to a file

DAQcount = 0



File I/O General Info

The T7 uses Unix-style file paths where the separator character is a slash: /

The use of absolute and relative paths is supported, for example to read a file named "test.txt" from the "tmp" folder which is saved in the root directory use the following path:


If the current working directory is already set to "/" then you could also use the path:


Common File I/O Operations

See the Register Listing section below for register information.

Get the name of the current working directory (CWD):

  1. Write a value of 1 to FILE_IO_DIR_CURRENT. The error returned indicates whether there is a directory loaded as current. No error (0) indicates a valid directory.


  3. Read an array of size FILE_IO_PATH_READ_LEN_BYTES from FILE_IO_PATH_READ.

  4. Resultant string will be something like "/" for the root directory, or "/DIR1/DIR2" for a directory.

Get list of items in the CWD:

  1. Write a value of 1 to FILE_IO_DIR_FIRST. The error returned indicates whether anything was found. No error (0) indicates that something was found. FILE_IO_NOT_FOUND (2960) indicates that nothing was found.

  2. Read FILE_IO_PATH_READ_LEN_BYTES, FILE_IO_ATTRIBUTES, and FILE_IO_SIZE_BYTES. Store the attributes and size associated with each file.

  3. Read an array of size FILE_IO_PATH_READ_LEN_BYTES from FILE_IO_PATH_READ. This is the name of the file/folder.

  4. Write a value of 1 to FILE_IO_DIR_NEXT. The error returned indicates whether anything was found. No error (0) indicates that there are more items->go back to step 2. Each of the following errors indicate that there are no more items:

  5. FILE_IO_END_OF_CWD (2966)


  7. FILE_IO_NOT_FOUND (2960)

Change the CWD:

  1. Find from the list of items a directory to open, e.g. "/DIR1".  Directories can be parsed out of the list of items by analyzing their FILE_IO_ATTRIBUTES bitmask.  If bit 4 of the FILE_IO_ATTRIBUTES bitmask is set, then the item is a directory. 

  2. Write the directory name length in bytes to FILE_IO_PATH_WRITE_LEN_BYTES (ASCII, so each char is 1 byte, also don't forget to add 1 for the null terminator).

  3. Write the directory string (converted to an array of bytes, with null terminator) to FILE_IO_PATH_WRITE.  (array size = length from step 2)

  4. Write a value of 1 to FILE_IO_DIR_CHANGE.

  5. Done.  Optionally get a list of items in the new CWD.

Get disk size and free space:




Get disk format:


  2. 2=FAT, 3=FAT32

Read a file:

  1. Write the length of the file name (including the null terminator) to FILE_IO_PATH_WRITE_LEN_BYTES

  2. Write the name to FILE_IO_PATH_WRITE (with null terminator)

  3. Write any value to FILE_IO_OPEN

  4. Read file data from FILE_IO_READ using the size from FILE_IO_SIZE_BYTES (FILE_IO_SIZE_BYTES can be read while getting a list of items in the CWD)

  5. Write a value of 1 to FILE_IO_CLOSE

Write a file:

Writing directly to the LabJack's installed SD card directly from the host computer is not supported. Most applications only need to create files from onboard Lua scripts.

  • For writing configurations to the LabJack, consider writing to the User Area of Internal Flash.

  • Other options for writing to an installed SD card include:

  • Generating and loading a custom Lua script as needed. Lua scripts can be loaded programmatically to the LabJack.

  • Writing a more generic Lua script that reads input from User RAM.

Create a directory:

Unimplemented.  Since Lua scripts currently do not have the ability to write files anywhere except the root directory, this feature is not implemented.

Register Listing

Read from the disk information registers to get free space and other information.

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