WITMOTION WT901C(RS232) Inclinometer Sensor User Manual

Tutorial Link

For tutorials and demonstration videos, please refer to the following links:

• Google Drive
• WITMOTION Youtube Channel - WT901C Playlist

If you encounter technical problems or cannot find the information you need, please contact the WITMOTION support team. Their engineering team is committed to providing the necessary support to ensure your success with 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 size makes it ideal for industrial retrofit applications such as condition monitoring and predictive maintenance. By interpreting sensor data through smart algorithms, the device can be configured for a broad variety of use cases.

The WT901C is scientifically known as an AHRS IMU sensor. It measures 3-axis angle, angular velocity, acceleration, and magnetic field. Its primary strength lies in its algorithm, which accurately calculates three-axis angles.

The WT901C is employed in applications requiring the highest measurement accuracy and offers several advantages over competing sensors:

• 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) data for Acceleration, Angular Velocity, Angle, and Magnetic Field.
• Low cost of ownership: Offers remote diagnostics and lifetime technical support from the WITMOTION service team.
• Developed resources: Includes tutorials, datasheets, demo videos, free Windows software, and sample code for MCU integration (Python, STM32, Arduino, Matlab, Raspberry Pi, C++), along with 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

Please observe the following safety precautions:

• Applying more than 5 Volts across the sensor wiring from the main power supply can lead to permanent damage to the sensor.
• Connecting VCC directly to GND will burn the circuit board.
• For proper instrument grounding, use WITMOTION with its original factory-made cable or accessories.
• For secondary developing projects or integration, use WITMOTION with its compiled sample code.

2 Instructions of 2023 New Software

To enhance user experience and customer service, a new version of PC software has been developed. The download link for the new software and universal instructions is provided below:

WITMOTION New Software (Universal) Download Link

The 2022 old version software will remain available. For details, refer to "Chapter 3 Use Instructions with PC".

3 Use Instructions with PC

The PC software is compatible only with Windows systems.

WT901C Playlist

3.1 Connection Method

3.1.1 Serial Connection

Step 1: Connect the sensor with a serial converter

PIN Connection:

• VCC: 5~36V
• TX: Yellow wire
• RX: Green wire
• GND: Black wire

(When connecting with a computer, VCC of 5-36V is recommended.)

Wiring Diagram Description: A diagram shows the RS232 PIN DEFINITION with color codes (RED for VCC 5-36V, YELLOW for TX, GREEN for RX, BLACK for GND). It illustrates the connection from a power source (5-36V) and the sensor to a serial converter, indicating VCC, TX, RX, and GND connections.

Recommended Tools

The following tools are recommended for connection:

• 3-in-1 converter
• 6-in-1 converter
• RS232 serial cable

Step 2: Unzip and install the software and driver. Install the CH340 or CP2102 driver, depending on your accessory.

• Link to tutorial of 3-in-1 serial converter/ RS232 serial cable (CH340 driver)
• Link to tutorial of 6-in-1 serial converter (CP2102 driver)

Step 3: Plugin the converter to the computer and confirm the "com port" in Device Manager.

Device Manager Description: A screenshot of the Windows Device Manager is shown, listing various device categories. The "Ports (COM & LPT)" section is expanded, showing "Silicon Labs CP210x USB to UART Bridge (COM15)", indicating a detected serial port.

Step 4: Open the software (Minimu.exe). Data will appear after auto-search finishes.

Notice: If the connection is not successful, please operate manually. Choose the correct COM port and set the baud rate to 9600. Data will then be shown on the software.

3.2 Software Introduction

3.2.1 Main Menu

The main interface of the WITMOTION software displays the current sensor readings, including Angle X, Angle Y, and Angle Z values. It also features a 3D pose visualization and a compass rose. The menu bar includes options like File, Tools, Record, 3D, Config, Help, and Auto-search. The left panel typically shows connection status and device information.

Main Menu Table Description:

3.2.2 Menu of Configuration

The configuration menu allows detailed adjustment of sensor parameters. Key sections include:

• System: Reset to factory settings, Sleep function, Alarm function, Algorithm selection (6-axis or 9-axis), Installation Direction (Vertical/Horizontal), Instruction Startup.
• Calibrate: Options for Accelerometer calibration, Magnetic Field calibration, Reset Z-axis Angle, Gyro Auto Calibrate, Reset Height, and Angle Reference.
• Range: Settings for Acceleration (e.g., 16 g), Gyroscope (e.g., 2000 deg/s), Bandwidth (e.g., 20 Hz), and GPS Time Zone.
• Communication: Settings for Baud Rate (e.g., 9600), Output Rate (e.g., 10Hz), and Device Address.
• Content: Checkboxes to select which data types to output, such as Time, Acceleration, Velocity, Angle, Magnetism, Port, Pressure, Location, PDOP, Quaternion, Positioning Accuracy, and GPS Original.
• Port: Configuration for extended ports (D0, D1, D2, D3), pulse width, and cycle for PWM signals.

Configuration Menu Table Description:

3.3 Calibration

Preparation: Ensure the sensor is "Online" in the software.

Calibration on PC software is required for the first-time usage to ensure accuracy.

3.3.1 Accelerometer Calibration

Purpose: To remove zero bias from the accelerometer, improving measurement accuracy.

Methods:

1. Keep the module horizontally stationary.
2. Click the "Accelerometer calibration" button.
3. Click "Start calibration" and wait for approximately 3 seconds. The system will automatically calculate the calibration value.
4. After the data is stable, click "Finish calibration".
5. Click the "Write and save" button to save parameters to the sensor.
6. To confirm, click "Read parameter" to check the calibration data.

Result Check: After calibration, when the module is placed horizontally, the Z-axis acceleration should be approximately 1g, and the X and Y axis angles should be around 0 degrees.

3.3.2 Magnetic Field Calibration

Purpose: To remove zero bias from the magnetic field sensor, which can cause significant measurement errors and affect heading angle accuracy.

Preparation: Keep sensors at least 20cm away from magnetic and iron materials.

Methods:

1. Open the "Config" menu.
2. Click the "Magnetic Filed" calibration button and then click "Start calibration".
3. Slowly rotate the module 360 degrees around the X, Y, and Z axes. The software displays data plots (chartXZ, chartYZ, chartXY) showing the sensor's response.
4. After rotation, click "End calibration".

Successful Result: Most data dots should fall within the ellipse displayed on the charts. If unsuccessful, ensure there is no magnetic field interference.

3.3.3 Gyroscope Automatic Calibration

This calibration process calibrates the angular velocity. The sensor performs automatic calibration. It is recommended to inactivate automatic gyroscope calibration only if the module rotates at a constant speed.

3.3.4 Reset Z-axis Angle

This function allows resetting the Z-axis angle. It is useful for avoiding magnetic interference by switching to the 6-axis algorithm and then using the "Reset Z-axis angle" function.

The Z-axis angle is an absolute angle. Resetting it to 0 degrees makes the initial Z-axis angle relative. If the Z-axis drifts significantly, it can be recalibrated. Upon power-on, the Z-axis will automatically return to 0.

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

3.3.5 Reset Height to 0

This function is only available for modules with a built-in barometer (e.g., WT901B, HWT901B, WTGAHRS1, WTGAHRS2).

3.4 Configuration

3.4.1 Return Content

Setting Method: Configure the data return content according to user needs by selecting options in the configuration bar.

By default, the WT901C outputs acceleration, angular velocity, angle, and magnetic field.

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

3.4.2 Output Rate

The default return rate is 10Hz, supporting up to 200Hz. 10Hz means 10 data packets per second, with each packet being 33 bytes by default.

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

3.4.3 Baud Rate

The module supports multiple baud rates, with 9600 as the default. To change the baud rate, select the desired rate from the communication rate drop-down box in the configuration bar, ensuring it matches the PC software setting.

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

3.4.4 Data Recording

Method:

1. Click "Record" and then "Begin".
2. Click "Stop" to end recording.

Data Extraction: The recorded data can be extracted as a "txt" file.

Notice: Repeated "TIME" entries may occur due to low system time resolution. It is recommended to paste the data into an Excel file for proper ordering and analysis.

3.4.5 Data Playback

This function allows playback of recorded BIN files. A BIN file is created in the "recordFile" folder of the installed software each time recording is performed.

Playback Method:

1. Disconnect the sensor.
2. Click "File" and then "Load".
3. Choose the BIN file from the software installation path.
4. Click "Run". The playback rate can be adjusted during playback.

3.4.6 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 the "Sleep" option in the "Config" menu. Click "Sleep" again to release sleep mode.

3.4.7 Placement Direction

The default installation direction is horizontal. For vertical installation:

1. Rotate the module 90 degrees around the X-axis.
2. Place the sensor vertically.
3. In the "Config" menu, select "Vertical" for Install Direction.

3.4.8 Bandwidth

The default bandwidth is 20Hz.

Function:

1. 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.
2. A higher bandwidth setting helps solve data-repeating issues. For instance, with a 20Hz bandwidth and 100Hz retrieval rate, there might be repeating data. Increasing bandwidth beyond 100Hz can prevent this.

Example Waveforms Description: Screenshots show waveform plots. One with 20Hz bandwidth and 10Hz output rate appears steady. Another with 256Hz bandwidth and 10Hz output rate shows more fluctuation.

3.4.9 Restore Factory Setting

Operation Method:

1. Connect the WT901C module to the computer via a USB-TTL module.
2. Click the "Setting" tab and then "Restore Default".
3. Power on the module again after restoring factory settings.

Note: This method requires knowing the module's baud rate in advance. If the baud rate does not match, the instruction may not take effect. Try the short circuit method for recovery if needed.

3.4.10 6-axis/ 9-axis Algorithm

6-axis algorithm: Z-axis angle is calculated based on angular velocity integral, which may result in calculation errors.

9-axis algorithm: Z-axis angle is calculated and analyzed based on the magnetic field, 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.

Method:

1. Switch to the "6-axis" algorithm in the "Config" menu.
2. Perform "Accelerometer calibration" and "Reset Z-axis angle" calibration.

After calibration, the sensor can be used normally.

4 MCU Connection

The WT901C sensor can be connected to a Microcontroller Unit (MCU) for integration into various projects.

Connection Diagram Description: A diagram shows the WT901C sensor connected to an MCU. The connections are as follows: VCC to VCC, TX (from sensor) to RX (on MCU), RX (from sensor) to TX (on MCU), and GND to GND.

Sample Code:

• Link to download all sample code
• Link to sample code instructions demo