UM7 Orientation Sensor (AHRS)

Description

The UM7 orientation sensor is a third-generation Attitude and Heading Reference System (AHRS) from CH Robotics that 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 features an onboard microcontroller that combines sensor data using a sophisticated Extended Kalman Filter (EKF) to generate orientation estimates 500 times a second.

Two versions of the UM7 are available: the UM7 orientation sensor, which includes an enclosure, and the UM7-LT, which does not. The two versions are functionally equivalent, and both include a cable (even though it is only shown in one of the two pictures below).

UM7 orientation sensor.

UM7-LT orientation sensor.

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 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.

Details for item #2741

UM7 orientation sensor with included cable and U.S. quarter for size reference.

UM7 orientation sensor, bottom view showing optional expansion headers.

Product Comparison

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

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

CHR Serial Interface.

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

Communication

• Output data:
• Attitude and heading (Euler angles)
• Attitude quaternion
• magnetometer, accelerometer, gyro data
• GPS altitude, position, velocity (with optional external GPS)
• 3.3 V TTL serial interface (UART) with baud rates up to 921,600 bps 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 5 V systems that are guaranteed to read 3.3 V as high
• Transmits data using human-readable NMEA strings (up to 100 Hz broadcast), binary packets for higher efficiency (up to 255 Hz 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″ (27 mm × 26 mm × 6.5 mm)
• Weight: 0.12 oz (3.5 g) without cable
• Operating voltage: 4 V to 5.5 V
• I/O logic level: 3.3 V (with 5V-tolerant main UART pins, TX and RX)

Attitude and heading

• EKF estimation rate: 500 Hz
• ±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

Videos

In this video playlist, Caleb Chamberlain from CH Robotics shows how to get started with the UM7, configure its communication settings, and calibrate its magnetometer.

Specification

Dimensions

General specifications

Notes:

1. Excluding mounting tabs.
2. Without included cable; 10 g with cable.
3. Note: The main UART pins, TX and RX, are 5V-tolerant and can be used directly with 5 V systems that are guaranteed to read 3.3 V as high. The secondary UART and some of the SPI pins are NOT 5V-tolerant.

Resources

File downloads

• UM7 datasheet (2MB pdf)
Datasheet for the CH Robotics UM7 orientation sensor, revision 1.3 (released October 27, 2014).
• UM7 Quick-Start Guide (16MB pdf)
• CH Robotics Serial Interface v3.0.9

CHR Serial Interface.

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

(This software is open-source; CH Robotics will provide the source code upon request.)