The findit flashlight: Responsive tagging based on optically triggered microprocessor wakeup

Abstract

We have designed an active tagging system that responds to a coded optical beam from several meters away. The tags contain a minimalist microprocessor that ambiently operates in shutdown mode and, upon detecting particular frequency components in the AM-modulated interrogation beam, awakens to decode the incident digital message and produce an appropriate response. The lack of linear amplifiers means that these tags draw under 0.5 µA when sleeping, hence can operate up to 10 years on a lithium coin cell. Such devices are practical demonstrations of the potential of ubiquitous computing where common, nearly passive objects have a sense of identity and the ability to respond to external stimuli. In our example, the interrogator is a “flashlight”, with which one scans an area; when the light beam hits a tag programmed with a code that matches that sent by the interrogator, an on-tag LED flashes, indicating that the desired object is “found”.