Hi all,

I am currently working on the design for an ultrasonic sensor and so far, I am having trouble understanding how the receiver reacts to motion.

- What kind of signal is generated by the receiver?
- How does the signal change depending on motion?

I am currently trying to figure out what kind of circuitry I will need once I decipher what kind of signal I am dealing with.

Any help is appreciated.

Thanks

 

hi 306,
Read thru these two PDF's ask if you have any questions.
E

 

hi 306,
Read thru these two PDF's ask if you have any questions.
E

Hi

I am familiar with HC SR04 ultrasonic nodules, however, the scope of this project involved designing one from scratch for movement detection rather than distance.

My question was geared towards the transducer itself rather than the whole module. We are currently supplying the transmitter with a 40kHz square wave but I would like to understand how the receiver reacts to the transducer sending signals.

What kind of signal should I see if I probed the voltage at the receiver and now that signal is affected depending on movement.

Thanks

 

hi,
Ok,
As you know the transmitter sends out a short burst of 40kHz pulses, if these pulses hit a target, some of the signal is reflected back to the receiver.
This signal is a weak 40kHz sine wave, which requires amplifying, is this what you are asking.?


E

 

If you want to detect motion of a target rather than just its pesence then you need to look for the doppler frequency change of the reflected signal. This might be difficult as the standard sensors are quite sharply tuned to 40kHz so frequencies away from that would be attenuated.

 

hi,
Ok,
As you know the transmitter sends out a short burst of 40kHz pulses, if these pulses hit a target, some of the signal is reflected back to the receiver.
This signal is a weak 40kHz sine wave, which requires amplifying, is this what you are asking.?


E

 

Yes this answers my question.

Now how does this signal change based on the detection of movement?

 

hi,
Movement of the target towards the transmitter shortens the time between the transmission time and the received time. the opposite happens if the target is moving away from the transmitter.
E

 

hi,
Movement of the target towards the transmitter shortens the time between the transmission time and the received time. the opposite happens if the target is moving away from the transmitter.
E

Gotcha. So does this change the amplitude of the sine wave?

 

hi,
Yes, the reflected energy is very weak, it also depends upon how well the target reflects.
Don't forget the pulse has to travel double the distance of the distance of the target to the transmitter.
E

 

A camera would be better for detecting motion, or, depending on what type of motion you are talking about, a passive IR sensor.

Bob

 

hi,
Yes, the reflected energy is very weak, it also depends upon how well the target reflects.
Don't forget the pulse has to travel double the distance of the distance of the target to the transmitter.
E

Got it. Thanks for the explanation

 

hi,
Can you say what is your application, we may be able to help out.
E

 

hi,
Can you say what is your application, we may be able to help out.
E

The application will be to drive an LED in a room. When the device detects a person, it will turn it on.

 

hi,
Ok, ultrasonic detectors can be over sensitive, triggered by moving curtains near a window etc...
Are you using two transducers one for TX and one for RX, pointing say across a doorway entrance.?
TX at one side and the RX at the other side of the entrance.
E

 

hi,
Ok, ultrasonic detectors can be over sensitive, triggered by moving curtains near a window etc...
Are you using two transducers one for TX and one for RX, pointing say across a doorway entrance.?
TX at one side and the RX at the other side of the entrance.
E

That pert has not been specified yet. The project is in very early prototyping stages. We still need to figure out how the signal will be processed in order to drive the LED.

 

hi,
Ok, ultrasonic detectors can be over sensitive, triggered by moving curtains near a window etc...
Are you using two transducers one for TX and one for RX, pointing say across a doorway entrance.?
TX at one side and the RX at the other side of the entrance.
E

That part can also be fixed with a micro controller timer since we are planning on implementing one

 

A passive IR motion detector would do this better. This is exactly what they are intended to do.

Bob

 

If you need to know relative position, you’ll need more than a passive IR motion detector (will tell you there’s motion, but not location), or ultrasonic sensors (will tell you the distance of an object, but also not location.)

You’ll need three ultrasonic receivers with one ultrasonic sensor to use triangulation to determine location. There is a hack with three HR04s to get this configuration (I have the link somewhere, but have to find it). Or you can remove the HR04s transmitters on the outer sensors.

You want 1 transmitter and 3 receivers equidistant from the center sensor/transmitter.

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

I’ve been working on this for a while, but found that using one HR04 rotated by a servo worked well enough for me. That solution provided polar coordinates which can then be converted to Cartesian. You may or may not be able to rotate your sensor.

Just my 2 cents...

dj

 

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