USER MANUAL WT901C(RS232)

Inclinometer Sensor

Tutorial Link: http://wiki.wit-motion.com/english ?

Contact: For technical support or information not found in the documentation, contact the WITMOTION support team. Our engineering team is committed to providing necessary support for successful operation of our AHRS sensors.

Applications: 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 that detects 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 with smart algorithms, customers can address a wide variety of use cases.

The WT901C'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 accurately calculates three-axis angles. The WT901C is employed where high measurement accuracy is required.

Key advantages include:

• Heated for best data availability: Features WITMOTION's patented zero-bias automatic detection calibration algorithm, outperforming traditional accelerometer sensors.
• High precision output: Provides Roll, Pitch, Yaw (X Y Z axis) data along with Acceleration, Angular Velocity, Angle, and Magnetic Field.
• Low cost of ownership: Offers remote diagnostics and lifetime technical support from the WITMOTION service team.
• Developed tutorial resources: Includes manuals, datasheets, demo videos, free software for Windows computers, an Android smartphone app, and sample code for MCU integration (e.g., 51 serial, STM32, Arduino, Matlab, Raspberry Pi), along with a communication protocol 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's main power supply wiring can cause permanent damage.
• VCC must not be connected directly to GND, as this will lead to circuit board damage.
• For proper instrument grounding, use WITMOTION with its original factory-made cable or accessories.
• For secondary development or integration projects, use WITMOTION with its compiled sample code.

2 Use Instructions with PC

2.1 Connection Method

The PC software is compatible only with the Windows operating system. For connection tutorials, refer to the WT901C Playlist.

2.1.1 Serial Connection

1. Step 1: Connect the sensor with a serial converter.
   PIN Connection: VCC - 3.3~5V, TX - Yellow, RX - Green, GND - GND. (When connecting with a computer, VCC-5V is recommended.)

Recommended tools:

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

2. Step 2: Unzip the software and install the appropriate driver (CH340 or CP2102, depending on the accessory used). Links to tutorials for CH340 and CP2102 drivers are available.
3. Step 3: Plugin the converter to the computer and confirm the "com port" in the device manager.
4. Step 4: Open the software (Minimu.exe). Data will appear after the auto-search finishes.

Notice: If the connection is unsuccessful, manually select the correct COM port and set the baud rate to 9600. Data should then be displayed on the software.

2.2 Software Introduction

A link to download the software is provided.

2.2.1 Main Menu

The software's main menu includes the following functions:

2.2.2 Menu of Configuration

The configuration menu allows for various settings:

Menu of System Function

Instruction Start-up: This function prevents data conflicts with the mouse when the module connects to the computer, which can cause mouse jumping. Enabling this function takes effect on the next module use or after a power cycle.

Menu of Calibrate Function

Menu of Range Function

Menu of Communication Function

Menu of Content

Select which data content to output:

Menu of Port Extended

2.3 Calibration

Preparation: Ensure the sensor is "Online". Calibration is required for the first-time usage.

2.3.1 Accelerometer Calibration

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

Methods:

1. Step 1: Keep the module horizontally stationary.
2. Step 2: Click the "accelerometer calibration" button.
3. Step 3: Click "Start calibration" and wait for 3 seconds.
4. Step 4: Click "Complete Calibration".
5. Step 5: Judge the result: Confirm if there is approximately 1g on the Z-axis acceleration. After calibration, the X and Y axis angles should be accurate.

Note: When the module is placed horizontally, there is 1g of gravitational acceleration on the Z-axis.

2.3.2 Magnetic Field Calibration

Purpose: To remove the zero bias of the magnetic field sensor, which can cause significant measurement errors and affect the accuracy of the Z-axis heading angle if not calibrated.

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

Methods:

1. Step 1: Open the "Config" menu.
2. Step 2: Click the "magnetic field calibration" button and then click "Start calibration".
3. Step 3: Slowly rotate the module 360° around the X, Y, and Z axes accordingly.
4. Step 4: After rotation, click "End calibration".

Successful result: Most data dots will form an ellipse. If unsuccessful, ensure you are away from 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 to use automatic calibration unless the module is rotating at a constant speed.

2.3.4 Reset Z-axis Angle

Note: To avoid magnetic interference, you can switch the algorithm to 6-axis mode and then use the "Reset Z-axis angle" function. The Z-axis angle is an absolute angle; it uses the northeast sky as the coordinate system and cannot be relative to 0 degrees. Resetting the Z-axis to 0 makes the initial angle relative to 0 degrees. When the module is used and the Z-axis has significant drift, this calibration can be performed. Upon module power-on, the Z-axis will automatically return to 0.

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

2.3.5 Reset Height to 0

This function is only available for modules with a built-in barometer, such as the WT901B, HWT901B, WTGAHRS1, and WTGAHRS2.

2.4 Configuration

2.4.1 Return Content

Setting method: The content of the data return can be set according to user needs by clicking the configuration option bar and checking the desired data content to be output. For the WT901C, the default output 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 of the module is 10Hz, with the highest supported rate being 200Hz. A 10Hz rate means 10 data packets are returned per second. By default, one data packet is 33 bytes.

Note: If more data is returned and the communication baud rate is low, data transmission may be insufficient. In such cases, the module will automatically reduce its frequency and output at the maximum allowable rate. To achieve a high return rate, the baud rate should also be set higher, generally 115200.

2.4.3 Baud Rate

The module supports multiple baud rates; the default is 9600. To change the baud rate, select the desired rate from the communication rate drop-down box in the configuration bar, ensuring a correct connection between the software and the module.

Note: After changing the baud rate, the module will no longer output data at the original rate. Data will only be output when the newly changed baud rate is selected in the PC software.

2.4.4 Data Recording

Methods:

1. Step 1: Click "Record" and then "Begin".
2. Step 2: Click "Stop".
3. Step 3: Extract the data as a "txt" file.

Notice: Repeated "TIME" entries in the data may be caused by low resolution in the Windows system's time display. Changes in other data are correct. It is highly recommended to paste the data into an Excel file, which will display all data in the correct order.

2.4.5 Data Playback

New function: When a recorded file is created, a BIN file is generated in the record file folder within the software's installation path.
Recorded data playback method:

1. Step 1: Disconnect the sensor.
2. Step 2: Click the "File" button and then click "Load".
3. Step 3: Choose the original software installation path and load the Bin file.
4. Step 4: Click "Run" to play back the Binary file. The playback rate can be edited.

2.4.6 Standby and Wake Up

Sleep: The module pauses its operation and enters standby mode, reducing power consumption.
Wake Up: The module transitions from standby mode back to the working state. The module defaults to a working state. In the software's "Config" menu, click the "Sleep" option to enter sleep state; clicking "Sleep" again releases it from sleep.

2.4.7 Placement Direction

The default installation direction for the module is horizontal. If vertical installation is required:

1. Step 1: Rotate the module 90 degrees around the X-axis.
2. Step 2: Place the sensor vertically.
3. Step 3: Select "Vertical" as the installation direction in the "Config" menu.

2.4.8 Bandwidth

The default bandwidth is 20Hz.

Function:

1. A higher bandwidth setting leads to greater fluctuation in the data waveform. Conversely, a lower bandwidth results in smoother data. For example, with a bandwidth of 20Hz and an output rate of 10Hz, the waveform is very steady. With a bandwidth of 256Hz and an output rate of 10Hz, the waveform will show more fluctuation.
2. A higher bandwidth setting can resolve data-repeating issues. For instance, if the bandwidth is set to 20Hz and the retrieval rate is 100Hz, there will be 5 repeating data points. To avoid repeating data, it is necessary to increase the bandwidth to be more than 100Hz.

2.4.9 Restore Factory Setting

Operation method: Connect the WT901C module to the computer via a USB-TTL module. Click the "setting" tab and then click to restore the default settings. After restoring factory settings, power cycle the module.
Note: This method requires knowing the module's baud rate in advance. If the baud rate does not match, the instruction will not take effect. A short circuit method is available for recovery.

2.4.10 6-axis/ 9-axis Algorithm

6-axis algorithm: The Z-axis angle is primarily calculated based on angular velocity integration, which may introduce calculated error on the Z-axis angle.
9-axis algorithm: The Z-axis angle is calculated and analyzed based on the magnetic field, which may result in slight drift. The default algorithm for the WT901C is 9-axis. If there is magnetic field interference in the installation environment, it is recommended to switch to the 6-axis algorithm for angle detection.

Method:

1. Step 1: Switch to the "6-axis" algorithm in the "Config" menu.
2. Step 2: Proceed with "Accelerometer calibration" and "Reset Z-axis angle" calibration. The module can be used normally after calibration is completed.

3 Use Instructions with Android Phone

For APP configuration introduction, please refer to Chapter 2.2.

3.1 APP Installation

Install the APK file and grant permissions for Location and Storage. A link to download the Android APP is provided.

3.2 Hardware Preparation

Connecting with an Android smartphone requires a serial cable and a Type-C converter or OTG converter, depending on the phone's interface.

3.3 Connection

1. Step 1: Install the APK file and grant Storage permission.
2. Step 2: Connect the sensor with a TTL cable, then connect the cable with a Type-C converter. Plug the "Type-C converter" into the phone.
   Notice:
   1. After a successful connection, a notification "Choose an APP for the USB device" will appear, indicating the device has been detected. Select "WitMotion". "JUST ONCE" or "ALWAYS" is optional.
   2. Only the CH340 driver can be detected via the WitMotion APP.
3. Step 3: Open the APP and select "9-axis Series" as the sensor series.
4. Step 4: Select the baud rate as 9600. After selection, wait a few seconds for the data to display automatically.

3.4 Calibration

For calibration tutorials, refer to the WT901C-232 Playlist.

3.4.1 Acceleration Calibration

1. Step 1: Keep the module horizontally stationary.
2. Step 2: Click the "Calibration" menu.
3. Step 3: Click "Acceleration Calibration" and wait for 3 seconds.
4. Step 5: Judge the result: Confirm if there is 1g on the Z-axis acceleration.

3.4.2 Magnetic Field Calibration

1. Step 1: Click the "Calibration" menu.
2. Step 2: Click the "Magnetic calibration" button.
3. Step 3: Slowly rotate the module 360° around the X, Y, and Z axes accordingly.
4. Step 4: After rotation, click "Magnetic Calibration Finish".

Check the result: The Z-axis angle will show less drift than before.
Notice: If the calibration is unsuccessful, please move away from objects that can create magnetic field interference.

4 MCU Connection

Links to download all sample code and sample code instructions demos are provided.
Notice: Sample code is not currently provided for Linux or Python systems.

4.1 Arduino

Download link and Arduino UNO3 Demo Link are available.

4.2 STM32

Download link is available.

4.3 Raspberry pi

Tutorial link is available.

4.4 C#

DEMO link is available.

4.5 C++

DEMO link is available.

4.6 Matlab

Receive Sample Code and Dataplot DEMO are available.