Optical Range Finder Based on Position Sensitive Detector

Student: Craig Thomas Davies

Supervisor: Dr. Aleks Rakic

Category: Computer Systems Engineering Thesis Project

A range finder is any device capable of measuring the distance between two points. Optical methods to measure distance have a long history. There are several methods used to measure distance-using light. These include instruments based on the rangefinder principles such as fixed base and fixed angle. Other technologies include theodolites that use stadia tacheometry, tangent tacheometry and wedge attachments to theodolites. Finally there are devices such as self-reducing tacheometers, subtense bars and plane table alidades.

Based on the above technologies, the most important variable to determine range is the angle of incidence. The basis of this project is to design and build an inexpensive, accurate range finder that can measure the angle of incidence. The starting point of this project then is a Position Sensitive Device (PSD) manufactured by Hamamatsu Photonic Devices. This device is most sensitive to Infrared light of 920 nm.

An infrared laser pulsing at one KHz is used as the light source, which is incident on a target. A PSD based optical receiver collects the reflected light from the target. The PSD produces two current signals that are amplified and passed through a band pass filter. The two signals are read by two 12-bit analogue to digital converters on a National Instruments I/O Card inserted in a Personal Computer (PC). These two readings are manipulated by a software package, Lab View. Mathematical manipulation by Lab View converts the two signals into a range in centimetres.

The optical set up and the length of the PSD determine that range finder has a range of 34 – 64 cm in the prototype. At these two extremes, the received light spot goes past the ends of the PSD. Over this range accuracy is about 1%.

Poster Presentation (PDF)

Thesis Document (PDF)