:feet::back: An embedded sensor sole project.
Creating a new sense of balance by applying a live feedback of pressure sensors under the feet to alternative parts of the human body.
We use microcontroller platforms, pressure sensitive textiles, small vibrating motors, wireless communication, and a lot of creativity. Prototypes are all based on the Arduino platform and breakout boards.
The project implements interaction between two basic components:
Different kinds of generators (sensors) and consumers (actuators) can be combined using a common protocol. The value stream can be captured, intercepted, filtered, enhanced, augmented, visualized, or relayed using a smartphone or dedicated hardware to create arbitrary audio-visual feedback for therapeutic use cases or performance art.
In the first prototype the sensors and actuators communicate via serial link. A wireless link is provided over a Bluetooth LE serial connection. At first the connection is unidirectional from sensors to actuators. The sensors send a continuous stream of values. There is currently no need for a more sophisticated approach and this simplifies prototyping a lot.
The sensor value stream is sectioned off in packets. A packet has a header, followed by the raw uint16_t data values. The header consists of a magic value + a length field. Consumers (loggers/actuators) can scan the serial input for the magic value to synchronize on data start.
| Magic | Value | #values | value 1 | ... | value n |
|---|---|---|---|---|---|
uint8_t |
uint8_t |
uint8_t |
uint16_t |
... | uint16_t |
The length of a single packet is therefore 3 + (2 * #values) bytes.
The serial interface is usually limited to 115200 baud (bits per second) on fast interfaces. On lower end platforms this might be limited to 9600 baud. Assuming 64 values in a packet (131 bytes per packet), this translates to ~109 packets per second on a fast or ~9 packets per second on a slow serial connection. Accordingly we expect a best case packet latency of ~10ms (fast) / ~110ms (slow). This ignores all other overhead and marks expected lower bounds due to the communication interface.
Board: Adafruit Bluefruit nRF52 Feather central / peripheral bluetooth low energy (ble)
Input: 64 points of pressure sensitivity (10 bit ADC)
See the sensor_board/sensor_board.ino Arduino project.
See the actuator_board/actuator_board.ino Arduino project.
Thanks to the simple serial communication, we can use commodity hardware and very basic software to generate or consume the data streams.