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How to use ultrasonic sensors for measuring distance

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bmn123

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I read somewhere that ultrasonic sensors can be used to determine the distance to an obstacle.

If so, what are the sensors available in the market? Are there any alternatives? How do I implement the distance measuring circuit? I will be probably needing a digital output.
 

A.Anand Srinivasan

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Re: Ultrasonic sensors

in these kind of circuits you send a constant number of pulses towards a reflecting surface and you count the time taken for these pulses to come back multiplying the time taken by the velocity of sound you get twice the distance... now dividing it by two you get the distance...
 

    bmn123

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_i386sx25_

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Re: Ultrasonic sensors

Two ways to do it. First you can measure travel time, second you can measure reflected signals amplitude.

Travel time measurement is explained by the message above.For amplitude measurement, reflected signals amplitude is measured to determine distance. But you need and ADC, you need to calibrate system, plus reflection coefficent can be different for materials.

There is tranceivers around for robotics, usually working around at 40KHz. You can use them. Take a look at digikey.com and other mail order component sellers' calalogues.
 

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barry14

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Re: Ultrasonic sensors

Polaroid first came out with ultrasonic distance sensors which transmitted a series of short pulses at frequencies around 50 kHz. They used several pulses at slightly different frequencies to minimize false readings due to noise and other effects. These were used in their cameras to provide a means of automatic focusing. Nowadays, you can buy ultrasonic tape measures at Sears, Home Depot, and other department stores (or on line). They can measure out to 50-100 feet with fractional inch accuracy.
 

johnyaya

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Re: Ultrasonic sensors

To get an accurate distance you will need to know the air temperature. We use ultrasonic sensors to measure snow depth. We mount the sensor on a tower boom looking downward and as the snow accumulates the distance gets shorter. You must also make sure that you keep other objects out of the field of view of the sensor or account for their reflection in the processing.
 

bmn123

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Re: Ultrasonic sensors

Thanks for the help guys! I think I will use the time delay measurement scheme. I don't need to know the distance very accurately and the range over which I need to measure the distance is between 30cm - (150 to 200) cm.

Can you please tell me which are the most easily available sensors in the market and how to interface the sensor with the 8051 µC.
 

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Re: Ultrasonic sensors

timer circuits are already available in the microcontroller so you send out a fixed number of pulses and when you receive the same number of pulses back you can measure the time.... many ultrasonic transmitters and receivers and available in the market optimized for usage.... you can find these by browsing through company sites...
 

kender

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Re: Ultrasonic sensors

bmn123 said:
If so, what are the sensors available in the market? Are there any alternatives? How do I implement the distance measuring circuit? I will be probably needing a digital output.
There's an SRF family of small inexpensive ulrasonic range sensors. For example SRF08, which has an I2C interface: http://www.acroname.com/robotics/parts/R145-SRF08.html
 

vijaya_narayana

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Re: Ultrasonic sensors

U can use the any sensors for this purpose u can just measure the time between the instant of transmitting till u receive the signal and multiply with the speed of sound i think u will get the distance.The circuit is avaliable in the internet and there are a lot of sample program avaliable in the internet
 

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