SensorStreamer

Our phones are full of useful sensors - accelerometer, gyroscope, magnetometer... Every hacker have surely experienced the need to test something with one of these sensors. Usually you take Arduino with a sensor breakout board and you write a small piece of code, which send data to serial line.

But not always you have the sensors you need and the wires are sometimes a limitation. Here comes SensorStreamer - lightweight Android app, which can log sensor data and send them over network to your computer, where you can analyze them e.g. with a simple Python script.

You can download the app at the Play Store: SensorStreamer

Supported Features

• streaming of values from any sensor in the phone (as far as the sensor is supported by Android API)
• stream data over TCP sockets in
  • client mode
  • server mode
• stream data in
  • JSON object
  • binary packet

Format of the JSON Packet

The packets contain a JSON object as the top level entity. This object contains a field for each sensor. Each sensor supplies two values:

• timestamp (in form of nano seconds)
• value which is either a single float value or a 3D array of floats. For precise meaning of these values, see Android Sensor Reference.

As it is impossible to capture value from multiple sensor at the same time, time-stamp is included for each sensor independently. There should be only small differences in this timestamps, however, if you application requires precise timing, this value might come handy.

Format of the Binary Packet

Binary packet is designed to be as simple and as compact as possible. The format is following:

[0x80] [timestamp 8 bytes] [sensor values 1 or 3 float] ... [sensor values 1 or 3 float]

Timestamp is optional and can be omitted. The sensors are in the exact same order as the configuration in app says. This packet contains only one timestamp in order to be as compact as possible.

Timing

Due to the restrictions of Android API, it no possible to specify an exact frequency for sensor reading. Only 4 modes are available with frequencies roughly 5 Hz, 16 Hz, 100 Hz and the fastest possible mode. Note, that there no guarantee on the timing - the sensor might not be able to deliver values faster. In such a case, the frequency is limited by the slowest sensor in the packet.

Python Client

There is a 3rd party Python tool to capture data: PhoneSensor.

Author

Developed as a quick dirty hack by Jan "yaqwsx" Mrázek, graphics made by Martin Mikšík.