Skip to content

IM19 Attitude Module

For certain GNSS Flex modules, users have the option to purchase a variant with IM19 attitude module. The optional, IM19 attitude module from Feyman Inc. (FMI) fuses MEMS IMU sensor data and GNSS RTK positioning to deliver high-precision attitude compensated measurements, with roll and pitch accurate to within 0.05 degrees. This kind of superb accuracy has widespread uses in industrial applications such as tilt RTK surveys (where RTK poles need not be held straight vertical as the IM19 can calculate a virtual digital level at any tilt angle), agriculture machine automation, and dead reckoning.

Features:

  • Power: 0.33W
  • Data Rate: 100Hz
  • IMU Accuracy: ≤1% * D（1σ, vehicle)
  • Gyroscope
    • ARW: 0.17°/√(h)
    • Bias Stability: ±4.5°/h
    • Range: ±1000°/s


  • Accelerometer
    • Speed RW: 0.04m/s/√(h)
    • Bias Stability: ±0.3mg
    • Range: ±16g
  • Roll and Pitch: ≤0.02°（1σ）
  • Heading/Yaw: ≤0.2°（1σ）
  • Initialization: 1s (95%)
  • Self-calibration Technique

Info

For more information, please refer to the IM19 datasheet.

Accuracy

When configured and calibrated, the IM19 attitude module can fuses IMU sensor and GNSS RTK positioning data to deliver compensated position. The accuracy, displayed in the table below, should also be considered when implemented.

Tilt Angle Accuracy
0° - 30° 1cm
30° - 60° 2cm

Tip

It is recommended that the IM19 module is placed in a stable temperature region and avoid convection with the outside air.

Hardware Overview

Once calibrated, the IM19 will output proprietary NMEA messages containing the compensated position and roll, pitch and yaw. However, it requires the Pulse-Per-Second signal and NMEA GGA, RMC and GST messages from the GNSS receiver; and information on the location of the GNSS antenna's phase center (APC) and the survey point, with respect to the IMU's origin.

IMU Position

The measurements below are general guidelines for the position of the IMU inside the IM19 attitude module, with respect to the layout GNSS Flex module. The origin for the IMU is 2.72mm in Y-axis and 5.72mm in X-axis from the center of the IM19 attitude module. Users should also consider the manufacturing tolerances of the board in reference to these measurements. For example, the edges of the PCB may not be at their exact and that the exact position and orientation of the IM19 attitude module will be affected by the reflow process.

IMU offset measurment

The IMU position offset, with respect to the IM19 attitude module and the GNSS Flex module.

IMU offset measurment

The IMU position offset as viewed from the bottom of the GNSS Flex module.

UART Interface

The diagram below, generalizes the connections of the UART interfaces between the GNSS receiver, IM19 attitude module, and the GNSS Flex headers. In general, the UART1 and UART2 interfaces of the IM19 attitude module will be connected to the UART3 and UART4 interfaces, respectively, of the GNSS Flex headers.

Depending on the GNSS receiver of the GNSS Flex module, the first two available UART interfaces of the GNSS receiver will usually be connected to the UART1 and UART2 interfaces, respectively, of the GNSS Flex headers. Additionally, one of the TX pins from the available UART interfaces of the GNSS receiver will be connected to the RX pin of the IM19 attitude module's UART2 interface to provide the RTK GNSS data. However, this can connection can be changed through jumpers on the GNSS Flex Module, if necessary.

UART Connections

UART connections between the GNSS receiver, IM19 attitude module, and the GNSS Flex headers.

Info

For information on the exact connections between the UART interfaces of the GNSS receiver, IM19 attitude module, and the GNSS Flex headers, please refer to the hookup guide for the specific GNSS Flex module.

Abstract

For the UART interface of the GNSS receiver that is connected to the IM19 attitude module, users will need to configure the UART port for the following settings:

  • Baudrate: 115200bps
  • Output NMEA Messages: GPGGA, GPRMC, and GPGST
  • Solution Rate: 1Hz

PPS Signal

The PPS1 signal from the GNSS receiver, is used to fuse the MEMS IMU sensor data with the GNSS RTK position data. The timing of the PPS signal should match the solution rate of the GNSS RTK position data.

Abstract

For the PPS signal from the GNSS receiver, users will need to configure the signal's timing to match the RTK GNSS solution rate:

  • Solution Rate: 1Hz

AT Commands

Below is a summary of the AT commands supported by the IM19 attitude module.

AT Command Description
AT+SYSTEM_RESET System reset
AT+SAVE_ALL Save the parameters
AT+UPDATE_APP Update module firmware, see attachment for protocols
AT+UPDATE_BOOT Update Bootloader，see attachment for protocols
AT+GNSS_CARD= Set the GNSS RTK receiver type:
  • HEMI, NOVTEL, UNICORE, OEM
AT+READ_PARA=SYSTEM/ALL Read parameters （SYSTEM/ALL）AT+LOAD_DEFAULT Loading default parameters
AT+AUTO_FIX=ENABLE/DISABLE Installation angle estimation in tilt measurement applications
AT+CLUB_VECTOR=X,Y,Z Set the RTK pole vector to map the position tothe end of the RTK pole
AT+NAVI_OUTPUT=UART1,ON/OFF Binary NAVI positioning output
AT+NASC_OUTPUT=UART1,ON/OFF Ascii type NAVI positioning output
AT+MEMS_OUTPUT=UART1,ON/OFF MEMS raw output
AT+GNSS_OUTPUT=UART1,ON/OFF GNSS raw output
AT+LEVER_ARM=``X,Y,Z Set the lever arm
AT+LEVER_ARM2=``X,Y,Z Set the lever arm, the input value will be automatically adjusted according to the estimated installation angle
AT+CHECK_SYNC Query whether time is synchronized between MEMS and GNSS
AT+HIGH_RATE=``ENABLE/DISABLE High-rate mode setting
AT+ACTIVATE_KEY=``KEY Module activation
AT+ALIGN_VEL=1.0 Set the initial alignment speed threshold
AT+VERSION Query the Firmware version
AT+GNSS_PORT=``PHYSICAL_UART2 Set the physical serial port for communicatingwith the GNSS RTK receiver. Save the Settings and restart to take effect
AT+WORK_MODE=``X Set the module working mode
AT+INSTALL_ANGLE=``X,Y,Z Set the module installation angle
AT+THIS_PORT Query the serial port number
AT+FILTER_STOP= ENABLE/DISABLE Causes the filter to enter or exitstop mode
AT+LOOP_BACK= UARTn/NONE UART n enters or exits the loopback mode
AT+FILTER_RESET Filter Reset
AT+CHECK_CRC= N The IM19EE firmware CRC is calculated for checkingthe firmware, where N is the firmware size
AT+CORRECT_HOLDER= ENABLE/DISABLE Turn on or off RTK pole length compensation
AT+OUTPUT_DISABLE= UARTx Disable the output of all messages over the serial port x
AT+CALIBRATE_MODE2= STEP1/STEP2 Factory calibration command
AT+SET_CHECK_LEVEL= LEVELx Set check level of calibration parameter
AT+FACTORY_PARA_x= X,Y,Z Recovery factory calibration parameter
AT+SET_PPS_EDGE= RISING/FALLING Set PPS edge, accept falling pps edge by default

Info

For more information, please refer to the IM19 integration manual.

Configuration Requirements

  • Access to the UART interfaces of the IM19 IMU

  • Access to configure the UART interface and PPS signal that are transmitting from the GNSS receiver to the IM19 IMU

    Abstract

    For the UART interface of the GNSS receiver that is connected to the IM19 attitude module, users will need to configure the UART port for the following settings:

    • Baudrate: 115200bps
    • Output NMEA Messages: GPGGA, GPRMC, and GPGST
    • Solution Rate: 1Hz

    The timing of the PPS signal from the GNSS receiver should match the RTK GNSS solution rate being transmitted to the IM19 IMU.

  • The location of the APC of the GNSS antenna and the survey point, with respect to the IMU's origin.

Info

For information on the antenna reference point (ARP) and antenna phase center (APC), check out this useful tutorial by Septentrio.

Tip

It is recommended that the IM19 module is placed in a stable temperature region and avoid convection with the outside air.

Compatible Software

Below are some compatible software options for configuring the IM19 attitude module and receiving the tilt-compensated position in its proprietary message format.

PyGPSClient

As of v1.5.8, a widget has been added to the PyGPSClient application to configure and utilize the IM19 attitude module.

Resources

For additional information, users can refer to the following resources for the PyGPSClient software:

IM19 IMU Arduino Library

The SparkFun IM19 Tilt Sensor Arduino Library can be installed from the library manager in the Arduino IDE by searching for:

SparkFun IM19 IMU Arduino Library

Library listed in the library manager of the Arduino IDE

SparkFun IM19 IMU Arduino Library in the library manager of the Arduino IDE.

Manually Download the Arduino Library

For users who would like to manually download and install the library, the *.zip file can be accessed from the GitHub repository or downloaded by clicking the button below.

Resources

Feyman Inc. also provides some resources for the IM19 attitude module: