Inspired by birds, TheSixthSense is an ankle device that gives wearers a better sense of direction.
Release a homing pigeon thousands of miles from home, and it’ll find its way back using its innate ability to sense the Earth’s magnetic field. Following the same principles, Maker Sebastian Foerster has developed what he calls “an extra sense for a better orientation.”
Initially inspired by his father’s balance disorder, TheSixthSense is an ankle-worn device that uses vibration motors to help guide a wearer in the right direction. Ideally, a gadget like this could one day prove to be invaluable for the visually-impaired, for those with a lack of orientation and in environments where there is limited visibility.
The wearable itself is comprised of a small, two-layer circuit board featuring an ATxmega32E5 at its core, along with an accelerometer, a magnetometer, a LiPo charger, a 2.5V LDO regulator and some MOSFETs to drive the set of vibration motors. TheSixthSense is also equipped with a 700 mAh LiPo battery, which boasts a life of about 30 hours before needing to be recharged. To program the system, Foerster employed Atmel Studio and the Atmel Software Library.
TheSixthSense must be calibrated before wearing. Once completed, the program is ready for magnetometer readings. Simply push its small button and turn the PCB around the different axis; push again and the calibration data is written to the EEPROM section. Beyond that, an accelerometer is used to make a tilt compensated compass, which means the exact position of the PCB on the anklet doesn’t matter all that much.
“However, the inconstant movement speed of the foot is a problem. When you walk the ground vector is moving with the acceleration of your feed. Since the acceleration is raising and falling in one step an additional filter is required to determine the true ground vector,” the Maker explains.
Once the magnetometer output is read, the two vectors can be used to calculate the angle to magnetic north. Afterwards, the correct motors are activated and set to the desired intensity.
“For my first test, I used four motors. As it turns out, four motors don’t work well enough when it comes to exact positioning. The shin isn’t sensitive enough to detect the small differences between two vibration sources. The solution for my second prototype is to use eight motors,” he adds.
“At the time, TheSixthSense works well and it is rather comfortable. I have been wearing it for three days during my time in the office and nobody could hear the vibration,” Foerster writes. “Nevertheless, in a noise free environment, it is loud enough to be heard by other people in the same room. It can be easily washed since all of the electronic parts can be taken out of the belt.”
Looking ahead, the Maker hopes to improve its filter, test adaptive vibration time, create a case for the circuit board and battery, as well as integrate Bluetooth Low Energy connectivity. More on TheSixthSense, which is currently a semi-finalist in this year’s Hackaday Prize, can be found on its project page here.