WITMOTION WT901C(RS485) Inclinometer Sensor User Manual
Model: WT901C(RS485)
Version: v0707
Tutorial Link
For tutorials and demonstrations, please refer to the following resources:
- Google Drive
- WITMOTION Youtube Channel
- WT901C RS485 Playlist
If you encounter technical issues or require further information, WITMOTION's engineering team is committed to providing the necessary support for the successful operation of their AHRS sensors.
Contact
For technical support, please refer to the Technical Support Contact Info.
Application
The WT901C sensor is suitable for a wide range of applications, including:
- AGV Truck
- Platform Stability
- Auto Safety System
- 3D Virtual Reality
- Industrial Control
- Robot
- Car Navigation
- UAV
- Truck-mounted Satellite Antenna Equipment
1 Introduction
The WT901C is a multi-sensor device capable of detecting acceleration, angular velocity, angle, and magnetic field. Its compact design makes it ideal for industrial retrofit applications such as condition monitoring and predictive maintenance. By interpreting sensor data through smart algorithms, the device allows users to address diverse use cases.
Scientifically known as an AHRS IMU sensor, the WT901C measures 3-axis angle, angular velocity, acceleration, and magnetic field. Its core strength lies in its algorithm for accurate three-axis angle calculation.
The WT901C is employed in applications requiring the highest measurement accuracy and offers several advantages:
- Heated for best data availability: Features a new WITMOTION patented zero-bias automatic detection calibration algorithm that 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: Offers remote diagnostics and lifetime technical support from the WITMOTION service team.
- Comprehensive development resources: Includes tutorials, datasheets, demo videos, free Windows software, and communication protocols for project development.
- Industry recognition: WITMOTION sensors are praised by thousands of engineers as a recommended attitude measurement solution.
1.1 Warning Statement
- Applying more than 5 Volts across the sensor wiring can cause permanent damage.
- Connecting VCC directly to GND will burn the circuit board.
- For proper instrument grounding, use WITMOTION's original factory-made cables or accessories.
- For secondary development or integration projects, use WITMOTION with its compiled sample code.
2 Use Instructions with PC
The PC software is compatible only with Windows systems.
2.1 Connection Method
2.1.1 Serial Connection
Step 1. Connect the sensor with a serial converter:
- PIN Connection:
- VCC - 3.3-5V
- B - B
- A - A
- GND - GND
(VCC 3.3-5V is recommended for connection)
RS485 PIN Definition:
The sensor has four pins:
- VCC (3.3-5V): Power supply input.
- A: RS485 Data A line.
- B: RS485 Data B line.
- GND: Ground connection.
A diagram shows a USB-to-RS485 converter connected to the sensor, with VCC, A, B, and GND lines clearly indicated.
Recommended Tools
Various serial converters are available:
- 3-in-1 converter
- 6-in-1 converter
- RS485 serial cable
Refer to tutorials for specific driver installations (CH340 or CP2102).
Connection Steps
- Unzip and install the appropriate driver (CH340 or CP2102).
- Insert the converter into the computer and confirm the COM port in the Device Manager. The Device Manager window shows a list of devices, including "Silicon Labs CP210x USB to UART Bridge (COM15)".
- Open the software (Minimu.exe). Data will appear after an auto-search.
Notice: If the auto-search fails, manually select the COM port and baud rate (9600) in the software.
2.2 Software Introduction
Download the software from the provided link.
2.2.1 Main Menu
The main software interface displays real-time sensor data, including Angle X, Angle Y, and Angle Z. It features several tabs and buttons:
| 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 Modbus for WT901C RS485 |
| Open | Open com port |
| Close | Close com port |
2.2.2 Menu of Configuration
The configuration menu allows detailed settings for the sensor:
| Button | Function |
|---|---|
| Read Config | Reading the current configuration |
| Lock | Lock the sensor |
| Unlock | Unlock the sensor |
| Calibrate Time | Calibration time of chip |
| Save Config | Save configuration |
System Settings:
- Reset: Reset to factory setting.
- Sleep: Sleep function.
- Alarm: Alarm function.
- Algorithm: Select between 6-axis or 9-axis algorithm.
- Install Direction: Set to Vertical or Horizontal installation.
- Instruction Startup: Instructions sending to start-up the sensor.
Instruction Startup Function: This feature prevents data conflicts with the mouse after connecting to the computer. It takes effect on the next module power-on.
Calibrate Settings:
| Button | Function |
|---|---|
| Acceleration | Accelerometer calibration |
| Magnetic Filed | Magnetometer calibration |
| Reset Height | Reset height data to 0 (for sensors with built-in barometer, e.g., WT901B, WTGAHRS2, WTGAHRS1, HWT901B). |
| Reset Z-axis Angle | Reset Z-axis angle to 0 degree (not available for WT901C in 9-axis algorithm). |
| Angle Reference | Set current angle as 0 degree. |
| Gyro Auto Calibrate | Auto-calibration of gyroscope. |
Range Settings:
- Acceleration: Acceleration measurement range (e.g., 16 g).
- Gyro: Gyroscope measurement range (e.g., 2000 deg/s).
- Band Width: Bandwidth range (e.g., 20 Hz).
- GPS Time Zone: GPS positioning of time zone (e.g., UTC).
Communication Settings:
- Baud Rate: Baud rate selection (e.g., 9600).
- Device Address: MODBUS device address (e.g., 0x50).
Display Interface (Port Settings): Configures output for D0, D1, D2, D3 models with pulse width and cycle settings.
2.3 Calibration
Preparation: Ensure the sensor is "Online" before calibration.
Calibration is required for the first-time usage via the PC software.
2.3.1 Accelerometer Calibration
Purpose: To remove the zero bias of the accelerometer, ensuring accurate measurements.
Methods:
- Keep the module horizontally stationary.
- Click the "Accelerometer calibration" button.
- Click "Start calibration" and wait for 3 seconds. The software displays X, Y, Z values and operating instructions.
- Click "Complete Calibration".
Step 5. Judge the result: Confirm if there is 1g on Z-axis acceleration. After calibration, the X and Y axis angles should be around 0°, and the Z-axis acceleration should read approximately 1g when the module is horizontal.
2.3.2 Magnetic Field Calibration
Purpose: To remove the zero bias of the magnetic field sensor, which can cause significant errors in heading angle measurements.
Preparation: Keep sensors at least 20cm away from magnetic and iron materials.
Methods:
- Open the "Config" menu.
- Click the "Magnetic Field" calibration button and then "Start calibration".
- Slowly rotate the module 360° around the X, Y, and Z axes.
- After rotation, click "End calibration".
Successful result: Most data points will be within the fitted ellipse. If unsuccessful, move away from potential magnetic interference.
2.3.3 Gyroscope Automatic Calibration
This calibration process calibrates the angular velocity. The sensor calibrates automatically. It is recommended to inactivate automatic calibration only if the module rotates at a constant speed.
2.3.4 Reset Z-axis Angle
This function is used to reset the Z-axis angle. If magnetic interference is a concern, switching to the 6-axis algorithm and using the "Reset Z-axis angle" function is recommended. The Z-axis angle is an absolute angle. Resetting it to 0 makes the initial angle relative. When the module is powered on, the Z-axis will automatically return to 0.
Calibration method: Keep the module static, navigate to "Config", select "Reset Z-axis Angle", and observe the Z-axis angle returning to 0 in the data bar.
2.3.5 Reset Height to 0
This function is only available for modules with a built-in barometer (e.g., WT901B, HWT901B, WTGAHRS1, WTGAHRS2).
2.4 Configuration
2.4.1 Baud Rate
The module supports multiple baud rates, with 9600 as the default. Select the desired baud rate from the communication rate drop-down box in the configuration bar to match the software and module connection. After changing the baud rate, the module will only output data at the new rate when it is selected in the PC software.
2.4.2 Standby and Wake Up
Sleep: The module enters a standby mode, reducing power consumption.
Wake up: The module returns to its working state from standby. By default, the module is in a working state. To enter sleep mode, click "Sleep" in the "Config" menu. Click "Sleep" again to release sleep.
2.4.3 Placement Direction
The default installation direction is horizontal. For vertical installation:
- Rotate the module 90 degrees around the X-axis.
- Place the sensor vertically.
- In the "Config" menu, select "Vertical" for the installation direction.
2.4.4 Data Recording
Method:
- Click "Record" and then "Begin".
- Click "Stop" to end recording.
A BIN file is created in the record file folder. The data can be extracted as a "txt" file.
Notice: Repeated "TIME" entries may occur due to low-resolution system time. Data is best viewed and ordered in an Excel file.
2.4.5 Data Playback
Recorded data playback method:
- Disconnect the sensor.
- Click the "File" button and then "Load".
- Navigate to the software installation path and select the BIN file.
- Click "Run". The binary file will be played back, and the playback rate can be edited.
2.4.6 Bandwidth
The default bandwidth is 20Hz.
Function:
- A higher bandwidth setting results in more fluctuation in the data waveform, while a lower rate makes the data more fluent. For example, 20Hz bandwidth with 10Hz output rate yields a steady waveform.
- A higher bandwidth setting helps resolve data-repeating issues. For instance, at 20Hz bandwidth and 100Hz retrieval rate, there might be 5 repeating data points. Increasing bandwidth beyond 100Hz is recommended for no repeating data.
A waveform plot shows data fluctuation at 20Hz bandwidth and more fluctuation at 256Hz bandwidth.
2.4.7 Restore Factory Setting
Operation method:
- Connect the WT901C module to the computer via USB-RS485.
- Click the "Setting" tab and then "Restore Default".
- Power on the module again.
Note: This method requires knowing the module's baud rate beforehand. If the baud rate doesn't match, the instruction may not take effect. A short circuit method is available for recovery.
2.4.8 6-axis/ 9-axis Algorithm
6-axis algorithm: Z-axis angle is calculated based on angular velocity integral, which may introduce errors.
9-axis algorithm: Z-axis angle is calculated and analyzed based on magnetic field data, which may have slight drift.
The WT901C defaults to the 9-axis algorithm. If magnetic field interference is present, switching to the 6-axis algorithm is recommended for angle detection.
Method:
- Switch to the "6-axis" algorithm in the "Config" menu.
- Perform "Accelerometer calibration" and "Reset Z-axis angle" calibration.
The sensor can be used normally after calibration.
2.4.9 Set MODBUS Address
The default address is 0x50 and can be changed via the software. Enter the new hexadecimal address in the MODBUS address configuration tab and click "Change".
Note: The MODBUS address change is not immediate; the device address needs to be searched again to take effect.
3 Multiple Module Cascades
The WT901C supports cascading multiple modules, allowing data from multiple devices to be viewed on the PC software.
Tip:
- Before cascading, change each module's MODBUS address individually via the PC software.
- If the BUS cable is too long, decrease the baud rate to reduce data packet loss.
Warning Statement:
- Ensure each sensor is powered with sufficient input voltage.
- Working voltage requires 3.3-5V input.
3.1 Hardware Connection Diagram
The diagram illustrates connecting multiple WT901C sensors in a cascade. It shows a laptop connected to a USB-RS485 converter, which then connects to up to 128 sensors. The wiring for cascading modules requires careful attention to VCC-VCC, A-A, B-B, and GND-GND connections.
3.2 Software Operation
To operate in a cascaded setup:
- Open the PC software.
- Select the model, serial port, and baud rate (9600).
- Click the "Search" button to find the devices. Multiple cascade device addresses can be searched.
Select the searched device address to view data from different modules. When cascading, remember each module's MODBUS address; rotating the module can help verify its data on the PC software.
