I have seen a lot of posts regarding how to send sensor data from Arduino to Android. But my question is how can I send sensor data from Android to Arduino using bluetooth. I know about the existence of the application Serial Bluetooth Terminal, but using this app I can only send text messages that I write, not real-time sensor values. I also know about Arduino Cloud, but in my project I need to use specifically bluetooth.
Is there another app that reads the sensors and sends the data via bluetooth? Or any other way?
You would need to have an App on the phone that reads the sensor and forwards it via Bluetooth.
If such an app doesn't exist, then you'll have to create one. I'd consider using the web-based AppInventor which is a very basic App development environment, but which is more than sufficient for this sort of project.
You'll find an introductory tutorial to AppInventor here and a Bluetooth/HC-05 tutorial here.
If you cannot send binary because of limitations on what is being sent you can send ASCII HEX, that would go through without a problem but you will need to convert it back at the receiving.
This one seems to do what the original poster is looking for without any additional development on the Android side: sesoduino or Arduino Serial Sensor
I've used AppInventor to write a simple App to display sensor data on the phone screen and I've written a Android terminal app that's a wireless Bluetooth terminal to a microcontroller with HC-05 on the serial port, so I'm certain that developing such an App is manageable in that environment, but may be unnecessary.