Abstract: An optical scanning rangefinder has been developed that creates a depth map of its surroundings by scanning a beam of modulated, collimated light and observing reflections from proximate surfaces. The scanning system uses dual rotating prisms to deflect the transmitted beam and collect a portion of the reflected light, which is focused on a photodetector and converted to an electrical signal. This signal is amplified, AC coupled, and inverted. The inverted signal drives the modulator for the light source. When sufficient light is received by the detector, this sytem forms an oscillator, the frequency of which depends on the distance to the illuminated surface. This frequency can easily be measured to a high degree of accuracy, and the distance to the surface derived from it. The scanner achieves a field of view of 360 degrees horizontally by 52 degrees vertically.