UM7-LT Orientation Sensor

Overview

The UM7-LT orientation sensor from CH Robotics produces attitude and heading estimates from triaxial accelerometer, rate gyro, and magnetometer data. Unlike a typical inertial measurement unit (IMU), which only provides raw sensor readings, the UM7 is a complete Attitude and Heading Reference System, or AHRS: its onboard microcontroller combines sensor data using an Extended Kalman Filter (EKF) to generate orientation estimates 500 times a second.

The UM7 features a number of improvements over its predecessor, the UM6, including higher gyro bias stability and lower noise, a new communication architecture for improved flexibility, optional NMEA packet transmission, UTC time-synchronization with external GPS, and support for third-order temperature compensation on all sensors. It takes advantage of newer MEMS (micro-electro-mechanical systems) technology that allows it to offer better performance at a lower price.

Connections for power and TTL serial communication can be made to the UM7-LT through a polarized five-pin male connector on one side, which mates with an included cable assembly. A pair of six-pin expansion headers on the other side of the board provide additional connectivity options, including an alternative SPI interface and a secondary serial interface that can be connected to an external GPS module (like our LS20031 GPS receiver). Additional cable assemblies for the expansion headers are not included.

UM7-LT orientation sensor, bottom view.

Cable included with the UM7-LT orientation sensor.

Product Comparison

We carry several inertial measurement and orientation sensors. The table below compares their capabilities:

Product Name	Sensors				Estimation				Other
	Gyros (3x)	Accels (3x)	Mag (3x)	Altitude	Roll	Pitch	Yaw	Quaternion	Enclosure
Pololu MinIMU-9 v3
Pololu AltIMU-10 v4
CH Robotics UM7-LT Orientation Sensor
CH Robotics UM6 r2 Orientation Sensor

Features

Sensors and processing

• Excellent gyro bias stability over temperature
• Adjustable low-pass filter and EKF settings provide customizable performance for various applications
• States and sensor data synchronized to GPS position and velocity using optional external GPS module
• Allows for alignment calibration and third-order bias and scale factor temperature compensation for accelerometers, gyros, and magnetometer
• Magnetometer soft and hard-iron calibration can be performed through the CHR serial interface software

Communication

CHR Serial Interface.

Graph of quaternions displayed by the CHR Serial Interface connected to a UM7-LT orientation sensor.

• Output data:
  • Attitude and heading (Euler angles)
  • Attitude quaternion
  • magnetometer, accelerometer, gyro data
  • GPS altitude, position, velocity (with optional external GPS)
• 3.3V TTL serial interface (UART) with baud rates up to 921,600bps can stream data or provide updates on request
  • Note: the main UART pins, TX, and RX, are 5V-tolerant and can be directly connected to 5V systems that are guaranteed to read 3.3V as high
• Transmits data using human-readable NMEA strings (up to 100Hz broadcast), binary packets for higher efficiency (up to 255Hz broadcast), or a combination of both
• Flexible communication architecture allows UM7 to transmit any combination of data at individually adjustable rates
• Connects to the CHR Serial Interface software to allow for real-time plotting of sensor data, logging, device configuration, and magnetometer calibration
• SPI interface available through expansion connector

Specifications

• Dimensions: 1.06″×1.02″×0.26″ (27mm×26mm×6.5mm)
• Weight: 0.12oz (3.5g) without cable
• Operating voltage: 4V to 5.5V
• I/O logic level: 3.3V (with 5V-tolerant main UART pins, TX and RX)

Attitude and heading

• EKF estimation rate: 500Hz
• ±1° typical static pitch/roll accuracy
• ±3° typical dynamic pitch/roll accuracy
• ±3° typical static yaw accuracy
• ±5° typical dynamic yaw accuracy
• 0.5° angle repeatability
• 0.01° angular resolution

Dimensions

General specifications

Notes:

1

Without included cable; 6g with cable.

2

Note: The main UART pins, TX and RX, are 5V-tolerant and can be used directly with 5V systems that are guaranteed to read 3.3V as high. The secondary UART and some of the SPI pins are NOT 5V-tolerant.