What is Time-of-Flight Technology?

Xabier Crespo

This summer we were one of the few companies selected to participate in the Connect 19 program to boost sales of our Ntouch line of products that have been designed to fight the spread of COVID-19. The program has helped us in many different aspects and we’d like to share part of it with our readers.

This is an engineering blog and we know our readers are here to read about tech and engineering but let me first tell you that thanks to Connect-19 and to ATDP agency, we have a new product logo and name (previously SC Touchless):

If you don’t know what I’m talking about, we have developed a set of devices that can be used with existing machines to interact with them in a safe manner. Imagine you’d like to order a drink from a vending machine or get some cash from the ATM. At the very least you will have to enter a numeric code by pressing the same physical buttons every user before you has touched. But don’t worry, we have a solution for that: our Ntouch Keypad is a plug-and-play solution that requires no modification in existing machines and can turn them into contactless devices.

Ntouch Keypad

If you would like to know more details of the Ntouch devices visit our portfolio page or reach out to us. We will happily talk with you.


But let’s now have a look at the Time-of-Flight (aka ToF) technology. We’ve become quite familiar with these sensors lately because they’re at the core of our contactless devices. On paper there are many other technologies that could solve this problem (capacitive, infrared, cameras, ultrasonic…) but ToF is the one that best fits our needs. We’ll try to guide you through the advantages.

DISCLAIMER: we do not use raw sensors but solutions like ST’s FlightSense™ which include the light transmitter, the receiver and also a small MCU to perform some initial algorithms.

You can think of ToF sensors as an evolution of widely used ultrasound sensors. However, instead of using sound waves they rely on LED lights in non-visible wavelengths. This fact gives them many advantages, including a longer maximum range and higher precision. The cost of ToF sensor solutions is significantly lower when compared to other alternatives like visible/infrared cameras, but at the same time more expensive than other sensors like infrared intensity or capacitive sensors. Nevertheless price is not the decisive factor for us.

The key advantage compared to other technologies such as the aforementioned ultrasound sensors, infrared sensors or even cameras, is ToF sensor’s higher immunity to light and ambient conditions. If you use one of the sensors from the first group in a noisy environment or a dark room you will end-up with many false results (positives and negatives). ToF technology can however work independently of target object reflectivity properties, a big problem for traditional infrared (IR) sensors.

Of course, not everything is perfect. For instance, a ToF sensors have quite low detection resolution (usually one or very few objects at best). ToF can also be affected by highly intense IR ambient light sources (namely, the sun). On the bright side, thanks to the manufacturers commitment and to our own experience we can now detect multiple targets with the same sensor, focus on a given area or mount them inside an IPX mechanical case…

To sum up, check the table below with the advantages and disadvantages of Time-of-Flight technology:

ProsCons
Relatively low costLow resolution
Small sizeSlow refresh rate
High precision and wide range
Noise and ambient conditions immunity
Low power (consumption and computation)
ToF pros and cons

If you would like to learn more about Time-of-Flight sensors go head and visit Terabee website, a well-known ToF solution provider that explains this technology in much more detail.

What about the applications though?

Ntouch Keypad and vending machines (source: Delikia)

As you can in the video above see we are already applying this technology to build contactless keyboards and thanks to this experience we are also experimenting with gesture recognition and capacity measurements. There are many other applications though:

  • Presence detection for computers, smartphones, home appliances or even entire rooms
  • Industrial or clean environment control panels
  • Sensing for industrial robots, flight assistance for drones…
  • Camera auto-focus adjust
  • Load management in logistics

I hope you’ve enjoyed this article. If you have a project, an idea or just want to talk about Time-of-Flight technology drop us a message and we will be delighted to discuss it with you.

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