Ultrasonic distance measurement and ultrasonic sensors

If you need to measure the distance to an object located at some distance in front of you, or to some major obstacle in a non-contact way, then you can use an ultrasonic sensor. Devices of this type are very easy to use, they are reliable and economical, while they do not require any consumables.

The principle of measuring distance is based here on the technology that some animals use simply because of the specific structure of their body and the characteristics of the environment. The main condition is that there is air between you and the object, the distance to which is measured.

The ultrasonic sensor generates individual sound pulses of the ultrasonic range, that is, those that are not audible to a person. And since these pulses propagate through the air, they move at the speed of sound.

As soon as this sound reaches the nearest boundary of the object opposite, it is reflected from it according to the principle of the appearance of an echo, and then the sensor, receiving the reflected signal, calculates the distance to the object from which the reflection occurred. First, the time elapsed between the sending of the signal and the moment it arrives back is recorded, then it is multiplied by the speed of sound, and after that it is divided by two.

Since the distance to the object is determined here by the time of propagation and return of the sound wave, the accuracy of measurements performed by the ultrasonic sensor is independent of interference.

In principle, any object that reflects sound can be detected regardless of its color and illumination. It can be a wooden fence or a glass window, a piece of stainless steel trim or polycarbonate. It doesn’t matter if there is fog in the path of the ultrasound, or if the membrane of the sensor sensor has light dirt. This will not affect the functioning of the sensor.

The first sketches on the topic of ultrasonic distance measurement can be traced back to 1790, when the Italian physicist Lazzaro Spallanzani found out that bats navigate and maneuver during flight even in total darkness, using hearing, and not at all vision.

The researcher made many observations of bats, made several experiments, thanks to which he came to the unequivocal conclusion that bats are oriented and navigate in complete darkness using ears and sound. So, Spallanzani was the first to study echolocation, starting with observations of bats.

Only in 1930, the American zoologist Donald Griffin, studying the sensory mechanisms of animals, finally confirmed that bats move even in complete darkness, using ultrasound for navigation purposes. It turned out that the bats themselves provide ultrasound in order to then hear its reflection, in order to understand where and at what distance in their path are objects, obstacles, insects, etc.

The scientist called this sensory-acoustic technique of bats navigation echolocation. As you probably remember from the school physics course, echolocation is generally called the technical use of ultrasonic waves and the study of their reflections (echoes) in order to determine the locations and sizes of objects.

By the way, not only bats, but also many nocturnal and marine animals and insects use ultrasonic frequencies to ensure personal safety, hunting and survival. Sound frequencies that are not audible to the human ear are so important in nature.

We return, however, to ultrasonic sensors. The module consists of an ultrasonic transmitter and receiver (like a bat’s ear).The transmitter serves to generate ultrasound radiation with a frequency of 40 kHz, and the receiver - to capture ultrasound at this frequency.

The transmitter is located on the board next to the receiver, so that it is able to perceive ultrasonic waves emitted by the receiver and reflected from the object in front of the sensor if there is air between the sensor and the object from which it is reflected.

When any obstacle enters the zone of action of the ultrasonic beam, the circuit calculates the time that elapses from the moment the ultrasound signal is sent until it arrives back - to the receiver.

This is easy to do, especially for electronics, because the speed of sound in air is known, it is 343.2 meters per second, therefore, multiplying the time by this speed, we get the length of the straight path along the path of the ultrasound from the receiver to the place of reflection and back.

Dividing into two - we get the distance to the reflection surface, regardless of whether it is hard or soft, color or transparent, flat or some kind of bizarre shape. And several of these sensors, located at right angles, will determine the size of objects.

Structurally, the sensor has two membranes, the first for ultrasound radiation, the second for echo reception. In essence, it is a speaker and a microphone. An ultrasonic frequency pulse generator is installed in the circuit, which starts the electronic timer at the moment the measurements begin, and as soon as the microphone receives the reflected sound, the timer stops.

Further microcontroller calculates the distance that the sound has traveled in the counted time. This distance will be twice the distance to the object, since the sound wave first went there and then went back. The result is shown on the display or fed to the next electronic unit.

Ultrasonic distance sensors are widely used in industrial engineering and in everyday life: detecting obstacles in the machine's operating area, ensuring car safety during parking, measuring distances during operation of machines and machines, during conveyor movements.

They help to determine the position of an object, material, water level, measure graininess, because ultrasound can be reflected from almost any surface if these surfaces do not absorb sound (as is done for example with special sound insulation or wool).

Ultrasonic sensors are especially popular today. with control on arduino in robotics, etc., simply due to the fact that these sensors (even several in one device) easily interface with many gadgets and, if desired, can be built into any automation system.

An example of creating a simple ultrasonic rangefinder at home: