Designing a Passive Lidar Detector Device

Summary

Characterization of the iPhone LiDAR[…] https://pmc.ncbi.nlm.nih.gov/articles/PMC10537187/pdf/sensors-23-07832.pdfSo we know it is a 60hz, 940nm infrared signal. We also know that it can be expected to present as a rotating pattern of lattice grid beams of light. Armed with this information, I began brainstorming different approaches to measuring such a signal in a meaningful way. It was at this point that I realized I actually don't really know how to do that, so I looked it up.LiDAR is a Flashy Light, How Do We Measure a Flashy LightAfter a lot of web searching, reading other researchers' existing work, reading a lot of Wikipedia pages, struggling to get good suggestions out of LLMs, and poring over datasheets, I reached a point where I felt I was beginning to understand the objectives well enough.See a signal as light spread into beams over an areaSense and convert that light to an analog signalConvert the signal from analog to digitalMeasure itThe iPhone TrueDepth uses a 60hz, 940nm VCSEL DotGrid Lattice LiDAR system. In order to detect this and distinguish it from other signal sources, a device would need to sense IR signals from multiple discrete sources at high speed from which several factors could be measured. Once these factors are measured, the device would need to be able to quickly perform calculations on the measurements and programmatically decide whether the measured signals are the desired target, or noise. The factors we would want to measure are signal frequency, pulse repetition frequency, whether the signal is steady or in bursts, and how many sensors detect the same signal at the same time or not.Now, armed with even more information I set about looking up what components might suit the needs of the project.HardwareThis device needs to detect 940nm infrared signals. I tested several ways to accomplish this, including LEDs wired as photodiodes with and without 940nm bandpass filters, pin silicon photodiodes with and without bandpass filters, and...