2 Description

As explained, the direct time of flight is a technique that measures the time (Δt) light takes to travel from source to an object and back. From this information, the distance of the object from the source can be determined. To implement this in hardware, we need a transmitter or source which can generate narrow high power light pulse, and a receiver sensitive enough to detect the weak echo optical pulse signal reflected after hitting the object. Both transmitter and receiver are typically placed next to each other facing the object whose distance has to be measured. This makes sure that the transmit path signal and the reflected path signal have the same distance to travel. In this way, the distance (d) of the object from the source is given by speed of light (c), multiplied by half the total time of flight (Δt) of the light pulse.

For this design, a laser (TL90AT03) is used as a light source, which is driven by TI’s laser driver, LMH13000. The LMH13000 pulses the laser to emit a short burst of infrared light. The optical output light from the laser is collimated using a lens and is then transmitted, which then travels through open space and gets reflected once the light hits any object in the path.

The reflected light is collected by a converging lens and focused onto an avalanche photodiode (APD), which converts the optical pulse into a small current. This current is then amplified and converted to a voltage signal using a transimpedance amplifier LMH32401, producing a clean electrical signal that represents the arrival of reflected pulse.