Laser Range Finders

Introduction

A laser range finder is a Triangulation sensor. It uses a laser diode as the light source and a linear photodiode array as the detector.

How it works

• the laser beam reflects off the object
• part of the reflected light goes through a detection slit on to the diode array
• the range is a function of the position on the array where the reflected light is at its maximum
• the emitter pin hole has a diameter of 0.5 mm
• the sensor has an active range of 5 to 60 mm, with reasonable accuracy

Key equations

In the figure, $h=24.5$ mm is the height of the detection slit above the diode array. $x_0$ and $x_i$ are distances along the array, measured from the laser source. $x_i$ is the position where the reflected light falls. The two triangles are similar, so:

$$\frac{\text{Range}}{x_0}=\frac{h}{x_i-x_0}$$ $$\boxed{\text{Range}=\frac{h{x}_0}{x_i-x_0}}$$