hi 0306,
Is this a College assignment project or Homework.?
E

Sorry for the late reply. It’s a college project.

 

hi,
Have you finalised the design.?
E

 

A single ultrasonic transmitter ‘pings’ the receivers. Each one will return a different distance which is then used to triangulate the position.
dj

But that assumes that the transmitter is mounted on the 'target'! The OP says "When the device detects a person, it will turn it on." So everyone would have to wear an ultrasonic transmitter!

Sorry - I'm not trying to be facetious, but I think this is outside the original requirement.

I am inclined to agree that a PIR sensor is far more suitable for this apllication.

 

But that assumes that the transmitter is mounted on the 'target'! The OP says "When the device detects a person, it will turn it on." So everyone would have to wear an ultrasonic transmitter!

Sorry - I'm not trying to be facetious, but I think this is outside the original requirement.

I am inclined to agree that a PIR sensor is far more suitable for this apllication.

No, no devices are mounted on the target.

 

General ultrasonic transducer receiving signal is at the same frequency of the output transducer. It tends to be a spike and then an asimtopic decay of the ringing. If you are using it for speed detection, it is a doppler effect and knowing the going frequency very accurately is key. Then doppler effect will either increase the frequency (coming closer), or reduce the frequency (going away).

Other option is to get a single response to identify a distance. Then do this again to see what the new distance is. Difference over time between measurements is speed.

DerekK

 

But that assumes that the transmitter is mounted on the 'target'! The OP says "When the device detects a person, it will turn it on." So everyone would have to wear an ultrasonic transmitter!

Sorry - I'm not trying to be facetious, but I think this is outside the original requirement.

I am inclined to agree that a PIR sensor is far more suitable for this apllication.

So, this sensor has both the transmitter and receiver. Three of them will allow you to determine the exact location of a person or object. Two have their transmitters removed, so the echo from transmitter on the third activates all three receivers. Calculating the distance from all three receivers allows accurate triangulation of the object /person reflecting the signal. Note (this is critical), nothing is located on the person/ object!

 

In order to detect motion, you need to detect the Doppler signal.
Study this link: https://www.slideshare.net/mobile/nanilamp/doppler-physics-by-dr-nani
Also look up Doppler in Wikipedia. Then search for "ultrasonic Doppler detection circuit", to get an idea of what's been done in the past. Here's one example: https://pdfs.semanticscholar.org/f001/d49fec6e960a9314eca2e03205e4906f152e.pdf
Can you come up with something better? That's your challenge.