A conceptual view of the PhotoBeacon system for robot localization.

PhotoBeacon Localization System

The PhotoBeacon system is meant to provide a simple means for localizing many (>50) small, autonomous mobile robots (in particular, we are targeting the CotsBots).  This system works using triangulation, or measuring the angles between robots. However, in addition to determining the bearing of other robots for localization purposes, the PhotoBeacon system can also be used to map obstacles or free space and provides a 1 kbps optical communication link between robots. In order to reduce the computational complexity generally required for localization, the PhotoBeacon system moves much of the complexity to hardware. The system is composed of four basic components: a high-power LED beacon to transmit, a fisheye lens to capture transmitted light from other robots in the horizontal plane, a custom CMOS sensor chip to detect signals from other robots, and a printed circuit board (PCB) with microcontroller to control the other components.


Design concept for PhotoBeacon system consisting of four separate components: the high power IR LEDs, a fisheye lens, the custom PhotoBeacon IC sensor, and a PCB with 8-bit microcontroller.

Die photo of PhotoBeacon IC fabricated in 0.25 um CMOS process.

PhotoBeacon IC

The custom PhotoBeacon Sensor IC is perhaps the most interesting and challenging design aspect of this system. This sensor needs to be able to detect very low power incident signals and resolve the relative angle to approximately 1º. In addition, the chip itself should be low power and provide a relatively simple interface to any external controllers.

The PhotoBeacon IC uses 256 photodiodes arrayed in the shape of an annulus to detect incoming signals. If light is focused onto a single pixel, the angle of incidence may be determined to approximately 1.4º. These photodiodes are multiplexed into a modified version of the 1 Mbps optical receiver designed by Brian Leibowitz which includes three switchable sense resistors and a gain stage which can provide up to 33 dB of gain. In addition, it also provides a way to discard DC current from ambient light. Finally, the receiver and multiplexor are controllable over a simple 3-wire serial interface. Simulations show the receiver detecting 1 kbps signals at under 100pW received power (equivalent to high power LEDs at 10m range).

Publications

Bergbreiter, S.; Pister, K.S.J. "PhotoBeacon: A localization system for multi-robot teams," submitted to ICRA 2007.


Sarah Bergbreiter
497 Cory Hall
UC Berkeley
Berkeley, CA 94720
sbergbre at eecs.berkeley.edu