Abstract
We propose Greendicator, an indicator system that augments embedded systems with display capabilities through cameras on smartphones. The transmitter encodes the message to be displayed in the form of light pulses emitted with an existing visible-light LED or other light-emitting devices such as IR, laser diode, or light re?ector as the emitter. The receiver uses a camera-equipped smartphoneto sense the light pulses and to decode the original message. Greendicator can be extended using the camera’s built-in ?ashlight as an acknowledgment to enable reliable communication. Greendicator enables virtually all embedded systems with an existing LED status indicator to convey both staticand dynamic messages while occupying a small footprint of only 1932 bytes of code memory and 128 bytes of data memory. The average transmission throughput of Greendicator is 5.7 bit/s and can be speeded up by the Table-encoding method, which costs 2.1 s to transmit a complete one of 16 messages of arbitrary lengths. Greendicator achieves practical decoding performance for its intended applications. On the iPhone 4S, Greendicator consistently achieves above 90% correct-decoding ratio in the distance test and angle test. An API is provided for programmers to incorporate Greendicator in their systems by simple function calls. We present the complementary support to existing RF-basednetworks by applying Greendicator to two real-running applications.