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Open Access Publications from the University of California

Development and Field Testing of Laser Photodiode Array-Based Vehicle Detection Systems


Over the past year we have researched the development of a network-based real-time laser-based nonintrusive field-deployable detection for the delineation of moving vehicles. The primary goal of this project is to develop a roadway detection system that can be used to gather reliable travel time data non-intrusively. A powerful Rabbit 3200, instead of multi-microchips, is used to control digitally controlled potentiometers (DCP), which adjust the gain of the sensors' signals. Utilizing digitally controlled potentiometers allow for quick and easy adjustment on the highway with only the need of pushing a button. The adjustment, which used to take half or an hour, now only takes several seconds. The Rabbit 3200 is also used as a data sender to a computer through the Ethernet. The rabbit digital input ports are triggered to collect the signals by an interrupt pulse from a PWM signal, which also acts as the laser source trigger. The Rabbit 3200 will then pack all of the data into TCP packages and send them to a remote computer over a network. The Rabbit 3200 is also able to filter noise after having finished the task of adjustment. The software of the system has been modified for 8 channels. Compared with the previous 4 channel code, the new system is able to obtain more information on vehicles, including the profile of a passing vehicle. In order to improve the precision of the system, we improved the mechanical design, optical design and electric circuit design. We also use an interrupt to sample signals instead of a fixed sampling interval strategy. This method ensures every signal generated by the APD will be captured by the Rabbit 3200. The laser sources are pulsed at 10 kHz and the sampling rate of the Rabbit 3200 is synchronized to the 10 kHz laser pulse. This report describes the design and implementation of each functional component of the field-deployable system, the configuration of the field detection system, software design and implementation, and a signal calibration method to obtain higher system precision. It also demonstrates four different ways to test the field-deployable system and the results from each way of testing for future improvement.

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