Haptic feedback refers to the force experienced when an object is touched or physically manipulated. It is an essential part of human interaction with physical objects, includ- ing electronic devices. Notably it provides a useful interaction channel independent of sound and vision, which are predominant in today’s digital interfaces.
Moreover, haptic feedback serves as a primary input modality to convey information when auditory and visual feedback may not be appropriate or available. However, with the exception of vibrating cellphone alerts, computer-controlled haptic feedback (sometimes called force feedback) it is not yet ubiquitous. Even so, other forms of haptic feedback, such as electronic control of temperature, stiffness and texture, are po- tentially valuable.
Unfortunately, the electric motors, solenoids, or other electromechanical actuators employed in many force feedback systems have significant power requirements. This seems inevitable since haptic feedback ultimately relies on electrical energy to affect physical movement. This in turn, limits mobile applications where battery life is an important fac- tor. As such, many of the haptic design schemes reported in the HCI literature require external power supplies.
We present Interactive Generator (InGen) , a self-powered wireless rotary input device capable of generating haptic or force feedback without the need for any external power source. Our approach uses a modified servomotor to per- form three functions:
(1) generating power for wireless communication and embedded electronics,
(2) sensing the direction and speed of rotation, and
(3) providing force feedback during rotation.
While InGen is rotating, the device is capable of providing the sensation of detents or bumps, changes in stiffness, and abrupt stops using only power that is harvested during interaction.
The TI eZ430-RF2500 platform with a MSP430 microcontroller and integrated CC2500 radio communications was chosen primarily on the basis of low power requirements and ease of use.
We make use of the optimized, low-power RF protocol stack called SimpliciTI for all wireless communication. To minimize power consumption, the transmit radio is only turned on briefly every 50 ms to beacon the speed and direction of interaction to the PC. The PC has a matching microcontrol- ler and radio that is always on. To ensure that InGen receives commands sent from the PC, every 5th wake up cycle (every 250 ms), the microcontroller turns on its receiver radio and polls for command messages.
A pending command is then executed before going into a low power mode again. More experimentation needs to be done to establish the ideal rate of polling, but we found that 250 ms provides a good tradeoff between interactivity and “device on” time.
To the best of our knowledge, InGen is the first self-powered device which also provides haptic feedback during operation. More broadly, this work demonstrates a new class of input systems that uses human-generated power to provide feedback to the user and wirelessly communicate sensed information.
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