Distance Sensing Overview

How do distance sensors work?

Distance sensors (or proximity sensors) generally work by outputting a signal of some kind, (eg laser, IR LED, ultrasonic waves) and then reading how it has changed on its return. That change may be in the intensity of the returned signal or the time it takes the signal to return. Some common terminology when talking about distance sensing include the following:

Resolution:

Resolution refers to the smallest change in distance that a sensor is able to detect. For example, an IR LED may have a resolution of about 5mm, while a VCSEL unit may have a resolution of about 1mm.

Update rate:

Usually measured in Hz, update rate comes into play with moving objects. the faster the refresh rate, the more reading per second the sensor will receive, important information if your sensor is traveling towards a fixed object at a high rate of speed.

Range:

Range is a distance, from minimum to maximum, that a sensor is capable of returning accurate readings.

How do interface options play a role?

Many things factor into deciding what interface option is best for a distance sensor project. The first is usually what type of sensor does your project require. Can you use an Ultrasonic Range Finder, or will you need to measure distances of over 20 meters? This may make the interface decision for you. However, if you do find yourself with multiple options, one of the main things to consider will be how many sensors you need vs. how many available pins you have. I2C will use two pins on your board, even if you're using multiple sensors (with different addresses), whereas SPI sensors will each need their own pin. Other considerations will include things like power consumption, speed, length of wire from board to sensor, and whether or not received data verification is necessary.