USER MANUAL

HWT901B(RS232)

Robust Inclinometer

WIT MOTION

Tutorial Link

Link to instructions DEMO:

If you have technical problems or cannot find the information that you need in the provided documents, please contact the WITMOTION support team. The engineering team is committed to providing the required support necessary to ensure successful operation of WITMOTION AHRS sensors.

Contact

Technical Support Contact Info

Application

AGV Truck
Platform Stability
Auto Safety System
3D Virtual Reality
Industrial Control
Robot
Car Navigation
UAV
Truck-mounted Satellite Antenna Equipment

1 Introduction

The HWT901B is a multi-sensor device detecting acceleration, angular velocity, angle, and magnetic field. Its robust housing and small outline make it suitable for industrial retrofit applications such as condition monitoring and predictive maintenance. Configuring the device enables users to address a broad variety of use cases by interpreting sensor data through smart algorithms.

HWT901B's scientific name is AHRS IMU sensor. It measures 3-axis angle, angular velocity, acceleration, and magnetic field. Its strength lies in its algorithm, which can accurately calculate three-axis angles.

The HWT901B is employed where the highest measurement accuracy is required. It offers several advantages over competing sensors:

Heated for best data availability: WITMOTION's patented zero-bias automatic detection calibration algorithm outperforms traditional accelerometer sensors.
High precision output: Provides Roll, Pitch, Yaw (X Y Z axis) Acceleration, Angular Velocity, Angle, and Magnetic Field data.
Low cost of ownership: Features remote diagnostics and lifetime technical support from the WITMOTION service team.
Developed tutorials: Offers manuals, datasheets, demo videos, free software for Windows, and sample code for MCU integration (including 51 serial, STM32, Arduino, Matlab, Raspberry Pi) and communication protocols for project development.
WITMOTION sensors have been praised by thousands of engineers as a recommended attitude measurement solution.

1.1 Warning Statement

Putting more than 36 Volts across the sensor wiring of the main power supply can lead to permanent damage to the sensor.
VCC cannot connect with GND directly, otherwise it will lead to the burning of the circuit board.
For proper instrument grounding, use WITMOTION with its original factory-made cable or accessories.
Do not access the I2C interface.
For secondary development projects or integration, use WITMOTION with its compiled sample code.

2 Use Instructions with PC

2.1 Connection Method

The PC software is only compatible with Windows systems.

Link to HWT901B's demo video

2.1.1 Serial Connection

Step 1. Connect the sensor with a serial converter.

PIN Connection:

VCC - 9~36V
TX - Yellow
RX - Green
GND - GND

(When connecting with a computer, VCC 9~36V is recommended.)

RS232 PIN DEFINITION:

RED: VCC 5V
YELLOW: TX
GREEN: RX
BLACK: GND

Wiring Diagram Description: A diagram shows a sensor connected to a power source and a serial converter. The sensor has pins labeled 1 (RED: 9~36V), 2 (YELLOW: TXD), 3 (GREEN: RXD+), and 4 (GND). These connect to the power source (POWER+, POWER-) and the serial converter's TX, RX, and GND pins respectively.

Recommended tools:

3-in-1 serial converter

6-in-1 serial converter

Link to tutorial of 3-in-1 serial converter (CH340 driver)

Link to tutorial of 6-in-1 serial converter (CP2102 driver)

Step 1. Unzip the software and install the driver CH340 or CP2102 (Depending on which accessory is used).

Step 2. Insert the converter into the computer and confirm the “com port” in the device manager.

Step 3. Open the software (Minimu.exe). Data will appear after auto-search finishes.

Notice: If not successful, please operate manually. Choose the correct COM port and baud rate (9600); data will then be shown on the software.

2.2 Software Introduction

Link to download software

2.2.1 Main Menu

The main software interface displays the WITMOTION logo, company name, and "Attitude Measurement System". It shows Angle X, Angle Y, and Angle Z values, along with buttons for Acc Calibrate and Alarm Set. A compass graphic is also visible.

Main Menu of Software Table:

Button	Function
File	Launch recorded HEX file (Bin format)
Tools	Hide or display tools box on left side
Record	Record function
3D	3D DEMO
Config	Configuration setting
Help	Language (English or Chinese)
	Bluetooth Set (Binding device or unbind)
	Firmware update (Option for firmware update)
	About Minimu (Info about Minimu.exe)
	Factory test (For manufacturer internal test only)
Auto-search	Auto searching the sensor
Port	Com port selection
Baud	Baud rate selection
Type	Fixed setting as Normal for HWT901B
Open	Open com port
Close	Close com port

2.2.2 Menu of Configuration

The configuration menu allows users to manage sensor settings. Key sections include System, Calibrate, Range, Communication, Content, and Port settings.

Menu of System:

Button	Function
Reset	Reset to factory setting
Sleep	Sleep function
Alarm	Alarm function
Algorithm	6-axis algorithm or 9-axis
Installation Direction	Vertical or horizontal installation
Instruction Start-up	Instructions sending to start-up the sensor

Menu of Calibrate:

Button	Function
Acceleration	Accelerometer calibration
Magnetic Field	Magnetometer calibration
Reset Height	Reset height data to 0 (only for sensor built-in barometer, including WT901B, WTGAHRS2, WTGAHRS1, HWT901B)
Reset Z-axis Angle	Reset Z-axis angle to 0 degree, not available for HWT901B in 9-axis algorithm
Angle Reference	Setting current angle as 0 degree
Gyro Auto Calibrate	Auto-calibration of gyroscope

Menu of Range:

Button	Function
Acceleration	Acceleration measurement range
Gyro	Gyroscope measurement range
Band Width	Bandwidth range
GPS Time Zone	GPS positioning of time zone

Menu of Communication:

Button	Function
Baud Rate	Baud rate selection
Output Rate	Return rate selection
Device Address	Interface for R&D

Menu of Content: Allows selection of data outputs like Time, Acceleration, Velocity, Angle, Magnetism, Port, Pressure, Location, PDOP, Quaternion, Positioning Accuracy, and GPS Original.

Menu of Port: Configures extended ports D0, D1, D2, D3, Pulse width, and Cycle.

Buttons for Read Config, Lock, Unlock, Calibrate Time, and Save Config are available.

2.3 Calibration

Preparation: Make sure the sensor is "Online".

Calibration on PC software: It is required to calibrate for the first time usage.

2.3.1 Accelerometer Calibration

Purpose: The accelerometer calibration is used to remove the zero bias of the accelerometer. Before calibration, there will be different degrees of bias error. After calibration, the measurement will be accurate.

Methods:

Keep the module horizontally stationary.
Click the accelerometer calibration button.
Click the "Start calibration" and wait for 3 seconds.
Click "Complete Calibration".

Software Interface Description (AccCal): The "Accelerator calibrate" window shows fields for X, Y, Z values and operating instructions. Buttons include "Read parameter", "Start calibration", and "Write parameter". The status area indicates calibration progress.

Result Confirmation: After 1-2 seconds, the three axial acceleration values should be approximately 0, 0, and 1g. The X and Y axis angles should be around 0°. When the module is horizontal, there is 1g of gravitational acceleration on the Z-axis.

2.3.2 Magnetic Field Calibration

Purpose: Magnetic calibration removes the zero bias of the magnetic field sensor, which can otherwise cause large measurement errors and affect heading angle accuracy.

Preparation: Sensors should be kept at least 20CM away from magnetic and iron materials.

Methods:

Open the Config menu.
Click the "Magnetic Filed" calibration button and then click "Start calibration".

Calibration Process: Slowly rotate the module 360° around the X, Y, and Z axes. After rotation, click "End calibration".

Successful Result: Most data dots will be within the ellipse displayed in the software. If not successful, move away from potential sources of magnetic field interference.

2.3.3 Gyroscope Automatic Calibration

The gyroscope calibration calibrates the angular velocity. The sensor calibrates automatically. It is recommended that automatic gyroscope calibration can be inactivated only if the module rotates at a constant speed.

2.3.4 Reset Z-axis Angle

Note: To avoid magnetic interference, you can switch to the 6-axis algorithm, which allows resetting the Z-axis angle. The z-axis angle is an absolute angle relative to the northeast sky. Resetting Z-axis to 0 makes the initial angle 0 degrees. If the z-axis drift is large, it can be calibrated. When powered on, the Z-axis will automatically return to 0.

Calibration Method: Keep the module static, click "Config", open the configuration bar, and then click "Reset Z-axis Angle". The Z-axis angle will return to 0 degrees in the module data bar.

2.3.5 Reset Height to 0

Only available for modules with a built-in barometer (e.g., WT901B, HWT901B, WTGAHRS1, WTGAHRS2).

2.4 Configuration

2.4.1 Return Content

Setting Method: The content of the data return can be set according to user needs. Click the configuration option bar and check the data content to be output. The default output for HWT901B includes acceleration, angular velocity, angle, and magnetic field.

Notice: If "GPS Original" is selected, no other data will be output.

2.4.2 Output Rate

The default return rate is 10Hz, with a maximum supported rate of 200Hz. 10Hz means 10 data packets per second, with each packet being 33 bytes by default.

Note: If there are many backhaul contents and the communication baud rate is low, data transmission may be limited. The module will automatically reduce the frequency to the maximum allowable output rate. For high return rates, a higher baud rate (e.g., 115200) is recommended.

2.4.3 Baud Rate

The module supports multiple baud rates, with the default being 9600. To set the baud rate, select it from the communication rate drop-down box in the configuration bar, ensuring it matches the connection between the software and the module.

Note: After changing the baud rate, the module will only output data when the new baud rate is selected on the PC software.

2.4.4 Data Recording

Method:

Click "Record" and then "Begin".
Click "Stop".
Extract the data as a "txt" file.

Data Extraction: The software interface shows recorded data streams. The extracted "txt" file contains timestamped data including acceleration, angular velocity, magnetic field, angle, pressure, etc.

Notice: Repeated "TIME" entries may occur due to low-resolution Windows system time; other data remains correct. It is recommended to paste the data into an Excel file for proper viewing.

2.4.5 Data Playback

New Function: Each recorded file creates a BIN file in the software's record folder. Recorded data playback method:

Disconnect the sensor.
Click the "File" button and then "Load".
Choose the original path of the software installation and load the BIN file.
Click "Run". The binary file will be played back, and the rate can be edited.

2.4.6 Standby and wake up

This function is accessed via the "Sleep" button in the System configuration menu, allowing the module to enter a low-power standby mode.

2.4.7 Placement Direction

The default installation direction is horizontal. For vertical installation:

Rotate the module 90 degrees around the X-axis.
Place the sensor 90 degrees vertically.
Click "Vertical" in the "Install Direction" setting within the "Config" menu.

The software interface shows the "Install Direction" dropdown menu where "Vertical" can be selected.

2.4.8 Bandwidth

The default bandwidth is 20Hz.

Function:

A higher bandwidth setting leads to more fluctuation in the data waveform. A lower bandwidth results in smoother data. For example, 20Hz bandwidth with 10Hz output rate provides a steady waveform.
A higher bandwidth rate helps resolve data-repeating issues. If the bandwidth is 20Hz and retrieval rate is 100Hz, there will be 5 repeating data points. To avoid repetition, increase bandwidth to over 100Hz.

The software interface displays bandwidth settings, and example waveforms for different bandwidths are shown.

2.4.9 Restore Factory Setting

Operation Method: Connect the HWT901B to the computer via USB to RS232 module, open the configuration bar, and click "Reset". After restoring factory settings, power on the module again. This method requires knowing the module's baud rate in advance; if it doesn't match, the instruction will not take effect.

2.4.10 6-axis/ 9-axis Algorithm

6-axis algorithm: Z-axis angle is calculated based on angular velocity integral, which may result in calculated error. 9-axis algorithm: Z-axis angle is calculated and analyzed based on the magnetic field, which may have slight drift.

The default algorithm for HWT901B is 9-axis. If magnetic field interference is present in the installation environment, switching to the 6-axis algorithm is recommended for angle detection.