Not receiving bluetooth sensor data

Hello, I am making a gait tracking sensor with the Arduino Uno. I have connected 5 MPU6050 IMU sensors to the I2C multiplexer and an HC-05 Bluetooth module to the Uno. One sensor measures hip motion, two measure knee motion, and two measure ankle motion. I have successfully uploaded the code that can make the calculations before I connected the HC-05, since I learned that having the HC-05 connected before uploading will cause error. I can connect to the HC-05 on my PC, however when I want to view the sensor data in the serial monitor, it is not showing. It keeps saying the COM port is busy. I have provided the code and a circuit diagram for reference. Please help me fix this issue. Thank you.

sketch.ino (7.92 KB)

mpu6050.h (2.69 KB)


There should not be any problem uploading a sketch so long as the HC-05 is not connected to the hardware serial port (pins 0&1). The IDE accesses that.

What are the available ports listed by the IDE? An HC-05 shows up as two ports and you need to figure out which one you select.

Are you sure you have paired the PC with the HC-05?


Thank you John,

In the IDE, the available ports are COM 6 and COM 7. I tried both ports, and according to the windows device manager, the HC-05 should be COM 6. When I connect to COM 7, nothing happens. COM 6 shows the error message still.

Does the LED on the HC-05 indicate it has connected to the PC?

My HC-05 blinks rapidly on power up and changes to blinking twice every 5 seconds when connected.


Yes, the HC-05 only blinks every 5 seconds, however the port is still busy. I am using Windows 10, and I searched for driver updates, but it says I have the latest drivers.

When I first pair the HC-05 to the computer, the LED flashes every five seconds, but when I click on done in the Bluetooth screen, the HC-05 goes back to fast flashing. Then when I go to the IDE and open the serial plotter on the COM6, it says port busy. The PC still is paired to the HC-05, and the COM ports are still available, however when I disconnect and reconnect the HC-05, the lights start flashing every five seconds even after I click on done. Then the PC removes the COM ports and I cannot select the HC-05 as a COM port anymore. I copied the error message below:

Arduino: 1.8.5 (Windows 10), Board: "Arduino/Genuino Uno"

Error opening serial port 'COM6'. (Port busy)