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I'm doing a project which using ultrasonic sensors to measure the distances to objects.

As far as I know the sensor can only measure the distance of the closest object to it. Is it right?

And in case there are multiple objects, can the ultrasonic sensor be able to detect distances to those?

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Typically ultrasonic sensors are designed to only return the distance to the first object. They send a pulse out, then time until that pulse comes back from a reflection, and that is the result. They ignore any remaining returns from other reflections.

It may be possible to modify or design your own ultrasonic sensor that pays attention to the other reflections as well, giving multiple outputs from multiple objects, but unless you control the environment carefully it can be very complicated to do well.

But the answer to your question is no, unmodified ultrasonic sensors do not perform multiple object detection.

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There are some sensors with an analog envelope output. Which enables you to detect all the reflections detected by the receiver. And of course you can allways just use a transmitter and receiver without additional electronics, so that you deal with the raw signals, and then extract from it whatever you want.

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Unltrasonic sensors have a cone in which they measure. The aperture is usually specified in the data sheet and quite wide. Within this cone, the closest object will give the "sensor reading", although objects on the bounds of the cone might not be recognized correctly.

So for getting a good idea of e.g. a robots surroundings, laser sensors mounted on a servo might be better. You can sweep the surroundings in well-defined steps with this thing.

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  • \$\begingroup\$ Thanks for the help. But the problem is I need to use the ultrasonic sensors because they consume less power than laser sensor. And i want to use those ultrasonic sensors to measure the distances of several objects. Any idea ? \$\endgroup\$ – bienle Apr 29 '14 at 8:53
  • \$\begingroup\$ Hmm. How big are the objects and what are typical distances? Are we talking few car-sized objects within several meters distance or navigating a tight maze with a shoe-box-sized robot? \$\endgroup\$ – arne Apr 29 '14 at 9:14
  • \$\begingroup\$ the object has the size of an apple, and the range is about 0.5 meter. And I want to measure the distances to multiple objects, however the sensors are fixed and can not be rotated or moved during the measurement. \$\endgroup\$ – bienle Apr 30 '14 at 6:58
  • \$\begingroup\$ @bienle So you have a fixed sensor that is oriented into a "field" with multiple "apples" and you want to measure the distance to all of the apples? I don't see a way to do that, but maybe someone with more experience with these sensors could pitch in. \$\endgroup\$ – arne Apr 30 '14 at 7:06

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