Blog  /  Time of Flight Sensor: What It Is and How it Works

Time of Flight Sensor: What It Is and How it Works

ToF Sensor

ToF Sensor

Source: Flickr

Have you ever heard of Time of Flight sensors working in cameras and phones, but you don't know what is and how it works? If yes, then you're in the right place. Contrary to its name, the time of flight sensor has nothing to do with measuring the flight of an aircraft. Instead, it's more of a sensor that measures distance.

However, if the concept of time of flight sensors confuses you, don't worry. In this article, we'll shed light on the time of the flight sensor circuit, how it works, and how to use it.

So, hang in there!  

What is the Time of Flight Sensor?

 

Time of flight sensors measures how long it takes to travel via a medium from one point to another. In other words, it measures the time it takes an object to cover a particular distance.

Usually, the time of flight sensor measures the time elapsed between the generation of a wave pulse and when it reflects off an object and returns to the sensors. Also, you can use different types of signals on the ToF sensor. But the more common signs you can find are light and sound.  

ToF Sensor Illustration

ToF Sensor Illustration

Source: Wikimedia Commons  

Additionally, you can find ToF sensors in time of flight cameras. These devices use time of flight measurements to calculate the distance between the environment and camera and generate images from individually-measured points.

The time of flight sensor is powerful for distance sensing and range finding–mainly when it emits light instead of sounds. Plus, when you compare ToF to ultrasound, you'll see that ToF offers faster readings, higher accuracy, and greater measurement ranges. The best part is that it packs all these features into its small, lightweight structure, and it doesn't consume much power.  

How Does Time of Flight Sensors Work?

 

ToF sensors measure the distance between an object and the sensor, as we mentioned earlier. And it uses a tiny laser that generates infrared light. Once it generates this light, it'll reflect off the surface of any object and move back to the sensor.  

Infrared Light

Infrared Light

 

Again, the ToF sensor measures the distance between the object and the sensor. Hence, it runs its basis on the time it takes the light to return to the sensor after bouncing off an object.

Indeed, that's what happens on the surface.

Thus, there are two ways ToF sensors can use the travel time to measure depth and distance. Also, you can use timed pulses and the phase shift of an amplitude-modulated wave to run the above measurements.

So, let's take a deeper look at the two methods of measurement:  

1. Using Timed Pulses

 

When a ToF sensor uses timed pulses to measure distance, it starts by firing a laser light at the target. Afterward, it uses a scanner to measure the distance traveled accurately.

Next, the sensor uses the different wavelengths and laser return time to generate an accurate 3D digital representation of the target's surface. Afterward, it creates a visual map of its features.

Also, the ToF sensor uses the following formula to deliver a precise measurement of distance:

(Speed of light x Time of flight) / 2  

2. Using Phase Shift of an Amplitude Modulated Wave

 

In truth, the ToF sensor can measure distance and depth by detecting the phase shift of the reflected light via continuous waves.

When the sensor modulates the amplitude, it generates a light source from a sinusoidal form.  

Sinusoidal form waves

Sinusoidal form waves

Source: Reasearchgate

The known frequency of this form enables the detector to measure the phase shift of the reflected light with the following formula:

Phase Shift Formula

For this formula, c is the speed of light (3×108 m/s), λ is the wavelength (15m), and f is the frequency.

Furthermore, the sensor works with the speed of light. So, you can imagine how fast and precise the sensor measures depth and distance.

However, the principle you choose doesn't matter. If you provide a light source to illuminate the scene, the sensor will measure the object's depth. Also, the results will create a range map where each pixel shows the distance to the matching point on the thing.  

Benefits of Using Time of Flight Sensors

 

Here are some of the advantages of using time of flight sensors for your distance-measuring applications.  

Long Range

 

Since ToF sensors work with lasers, they can measure long ranges and distances with extreme precision. For this reason, ToF sensors can detect both far and near objects of different shapes and sizes–making them flexible.

Also, its flexibility allows you to customize the optics of your system, so you're only getting optimal performance and the field of view you prefer.  

Cost-Effective

 

Regarding prices, ToF sensors are more budget-friendly than other 3D depth scanning technology. However, its lower price does not affect its capturing 3D information fast.  

Precise and Fast Measurements

 

Time of flight sensors leaves other distance sensors, like ultrasonic sensors, in the dust regarding speed and precision. ToF sensors can quickly detect objects and are resistant to air pressure, temperature, and humidity, making them perfect for indoor and outdoor use.  

Safe

You don't have to worry about lasers harming your eyes. Most ToF sensors feature low-power infrared laser lights and use modulated pulse to drive them. Plus, these sensors reach the class 1 laser safety standard–making it safe for the human eye.  

Limitations of ToF

 

As beneficial as ToF sensors are, several factors limit them. Here are some of these limitations:  

Multiple Reflections

 

If you're using your ToF sensor on concave shapes and corners, there's a chance you'll get unwanted reflections that alter the precision and accuracy of measurements.  

Ambient Light

 

Using ToF cameras in bright outdoor conditions, like sunlight, can create difficulties when taking measurements. Plus, the high intensity of the sunlight can potentially cause a quick saturation at the sensor pixels. In other words, the sensor will fail to detect when light reflects off an object.  

Scattered Light

 

If you have any bright surfaces near your ToF sensor, it could lead to the presence of scattering light in your receiver. Thus, it would create multiple unwanted reflections that could hinder measurement.  

Time of Flight Sensor Examples

 

Now you're familiar with how ToF sensors work, let's look at some of the best sensors you can use for your projects. These examples work for various applications, including automation and appliances.  

Opene8008B-QVGA Time-of-Flight Sensor Evaluation Kit

 

Opene8008B-QVGA Time-of-Flight Sensor Evaluation Kit

Opene8008B-QVGA Time-of-Flight Sensor Evaluation Kit

Source: Wikimedia Commons  

The Opene8008B-QVGA ToF evaluation kit is the perfect ToF camera that features high-resolution depth images. Plus, you can get real-time visualization and recording of depth map data by connecting this camera to a PC.

In addition, this ToF goes beyond the operating parameters of regular ToF cameras and reaches a maximum of 10m. Also, you can get coherent images with this ToF sensor since the camera's FPS maxes out at 120.

Furthermore, you can change IR filters within 850nm and 940nm. 850nm filters give you a better image view because of their high sensitivity. At the same time, a 940nm filter would help you reduce glow interference to provide you with an optimal depth image performance.  

TFmini Plus - ToF LIDAR Range Finder

 

TFmini Plus - ToF LIDAR Range Finder

TFmini Plus - ToF LIDAR Range Finder

Source: Wikimedia Commons  

Here's another great example that works best for single-point short-range distance ToF measurements. The TFmini plus LIDAR distance sensor can generate near-infrared rays to measure the difference between the emitted and reflected glare and get the ToF distance.

However, the LIDAR principle makes it hard for this sensor to give precise measurements between objects like glass or water. But its sensor is sensitive enough to measure the distance between a moving object and the TFmini in real-time.

Plus, you can get your distance data on your PC by simply plugging your TFmini via USB. Additionally, developers can take advantage of TFmini's UART and I2C interface.  

Slamtec Mapper ToF Laser Scanner

Slamtec Mapper ToF 

Slamtec Mapper ToF 

Source: Wikimedia Commons  

Need a ToF laser scanner; then this example is perfect for you. This scanner offers two different frameworks with different detection ranges:

  • 40m
  • 20m

The M1M1 is powerful enough to map scenes for home or commercial use and heavy-light locations.

You can also get real-time localization, top-notch mapping, and navigation functions from laser scanning. Plus, you can map external and internal scenes with this device.

This Slamtec scanner has fantastic performance, and it's straightforward with no hassles. You also don't need to depend on external tools. You only need to connect it to your PC or mobile phone, and you're all set.  

Are Time Flight Sensors Accurate?

 

The accuracy of any ToF sensor depends on how far the object is from the sensor. Also, you estimate the accuracy of a ToF sensor as 1% of the distance value. Thus, if your object is 8 meters away, the ToF sensor can get an accuracy of about 8 cm.  

Is LIDAR A ToF?

 

LIDAR is a form of ToF that uses pulsed lasers to generate point clouds that allow the sensor to create a 3D map image. Additionally, the LIDAR system uses an LED which you can direct to emit infrared light.  

Final Thoughts

 

You can use time of flight sensors for various applications, including industrial automation, autonomous vehicles, robotics, 3D mapping, gesture recognition, and even augmented reality.

Interestingly, there seems to be no end to applications that can use ToF sensors.

What do you think about the time of flight sensors? If you have any questions regarding the time of flight sensors, don't hesitate to contact us, and we'll be happy to help.