With an Uptick in Social Distancing Devices, Time-of-Flight Sensors May Simplify Designs

July 23, 2020 by Maya Jeyendran

Reopening businesses are honing in on social distancing. Time-of-flight proximity sensors may be the answer to cost-effective, easy-to-integrate designs for such use cases.

In the past, designing a device for distance measurement has been a costly and time-intensive process. According to a Digi-Key article on ToF (time of flight) sensors, some of the common technologies to accomplish this task have been infrared and ultrasonic sensors.

But such devices, which often implement AI for complex tasks like object recognition, are overboard for simple distance measurement tasks like movement detection on paper towel dispensers or access sensors on automatic doors. 

Finding a cost-effective solution for distance measurement is ever more important with an increasing focus on social distancing during the COVID-19 pandemic. Recently, STMicroelectronics teamed up with Amsterdam-based startup Aura Aware to rise to this challenge.


The VL53L1X, the ToF proximity sensor used in Aura Aware devices

The VL53L1X, the ToF proximity sensor used in Aura Aware devices. Image used courtesy of STMicroelectronics

Together, the two companies are employing ST's Flight Sense time-of-flight (ToF) technology for social distancing at retail counters and check-in desks. Aura Aware uses ToF technology within its own device to display a green “OK” signal when an appropriate distance is maintained between patrons and employees of a business; otherwise, a red signal is displayed. 


How Do ToF Sensors Promote Social Distancing?

A Texas Instruments ToF sensor system design explains simply how these devices work: as an emitter transmits modulated light pulses, that light bounces off objects and a portion of the reflected light returns to the receiver. The analog front-end of the device measures the roundtrip time of the light pulses to determine distance. 


Diagram of a standard ToF proximity sensor system

Diagram of a standard ToF proximity sensor system. Image used courtesy of Texas Instruments

ToF sensors are able to measure the duration of time it takes for a particular object to travel a distance through various mediums, too—for example, air or water. One unique feature of ST's new ToF devices is that it measures distance without respect to the reflectivity or color of the relevant object.


ST's ToF Sensor

STMicroelectronics’ ToF sensors include modern technologies such as single-photon avalanche photodiodes (SPADs) to receive light, surface-emitting lasers, infrared vertical-cavity, and more. These sensors are low-cost, unlike their two-dimensional, proximity-based counterparts, and they also report proximity measurements with 1 mm resolution to a host processor.

ST calls its VL53L1X (the device integrated into Aura Aware's devices), the "fastest miniature ToF sensor on the market." It operates from up to four meters away and includes built-in signal processing. The press release also claims that this device also offers crosstalk compensation and distance accuracy even if the sensors are obstructed by an object. 


Block diagram of the VL53L1X

Block diagram of the VL53L1X. Image used courtesy of STMicroelectronics

These ToF sensors comes with supplemental items: a microcontroller-based evaluation board, an expansion board that mounts atop a microcontroller board, and two corresponding breakout boards. To enable rapid development, sensors also come with example source code, extensive documentation, and an application programming interface (API) that is compatible with a multitude of processors and microcontrollers.

This straightforward development process may clear the way for a speedy design process and quicker time to market for social distancing devices that are increasingly in demand. 


How ToF Sensors Minimize Contact

The abilities of ToF sensors extend beyond social distancing. They can also be used to abate COVID-19 transmission by promoting little- to no-contact interfaces. For instance, these devices can be used for touchless swiping, touchless tapping, and touchless push-button door operation—minimizing the contact people have with common, high-touch surfaces.


Aura Aware social distancing device

Aura Aware social distancing device. Image used courtesy of Aura Aware

ToF sensors appear in a variety of other devices and situations governed by touchless interaction; for example, ToF sensors can be present in robotic vacuums and similar cleaning tools, autonomous vehicles for object detection, recognition devices, and laser-based scanner-less LiDAR imaging systems.



Have you seen a boost in no-contact designs in the past few months? What are the challenges of working with such systems? Share your experiences in the comments below.