Time Of Flight Measurement

1

Hi there,

I am starting out on a small DIY Project to be able to measure distance of objects using light and map it out in 3D.

I am using an IR LED with 940nm as its wavelength and a photodiode to capture the light and convert it into current. However I would like the photodiode to enable it to measure the time taken for the light to reach it i.e., the light leaves the LED at its own speed of C. It reflects of an object and some of its rays get scattered and some make their way to the photodiode. The LED will be pulsed i.e., will switch on/off at some clock frequency and a timer will start as soon as the light leaves.

I have hit a wall as to how I can measure the time it took the light to make its full flight back to the photodiode. I know there is an ADC converter needed somewhere but that is when I need to get the analog data already known and have it converted to binary.

Could someone please share their ideas and tips.

Many thanks,
Tony

2

This is not going to be an easy DIY project. The speed of light © is approximately 3x10^8m/s. If you were trying to measure ten meters you have (2 x 10) / (3x10^8) seconds before the pulse returns or ~66.7ns (6.67x10^-8 seconds). There’s a reason these sensors are very expensive. I found a simple description of how it all works here (https://www.allaboutcircuits.com/technical-articles/how-do-time-of-flight-sensors-work-pmdtechnologies-tof-3D-camera/).

I would recommend you purchase one of the TFmini TOF distance sensors Core-Electronics sell. I use these on my robots and they work very well.

1 Like