Human Detection

You can make motion detectors using ultrasonic transducers and dopler effect and they used to be popular in intruder alarms some 30 years ago before the mass uptake of passive IR which is generally cheaper and better.

With small 40kHz sensors you can (with care) manage a detection range of up to 10m. The design issues are to do with processing the analogue signals  - unless you get into very complex and sophisticated attempts to sort out noise from people I don't think that processing in the digital domain will do much good.

The problem is that the reflected signal from the target will be small at extreme range and quite big when close, the stray signal from the transmitting transducer picked up by the receiver will be large. Your analogue signal chain must have a large dynamic range and low noise.

If you really want to do the whole thing digitally I suppose you could, by using a 24 bit audio type ADC running at at least 200k samples per second - you still shouldn't need a DSP - and ARM Cortex M4 clocked at 150MHz gives you 750 processor cycles per sample which would allow some fairly fancy signal processing. Compared with an analogue bandpass filter (at about 40kHZ), a synchronous rectifier (to extract the doppler frequency) and some low frequency bandpass filters I think the all digital soultion will use far more power and cost a lot more.

As I recall from developing some of this stuff a  very long time ago the market leader (then) was made by Aritech and they used much larger transducers than the Murata ones (about 30mm diameter) and worked at about 30kHz rather than the 40 which seems common now.

I think our design used 3 quad op amps and  a handfull (about 5) of transistors.

MK

Thanks for the generous reply. but the problem with the pir sensor is that they can't differentiate between animals and humans and i want my system to detect humans with a fairly good accuracy rate . please suggest now.

Hello Anurag,

You coul try to use some kind of fixed obstruction in front of the pir sensor, to limit its range of vision. This way you can block the complete zone under, for example, 110cm. This is used in several commercial products to prevent burglar alarms from detecting cats or dogs walking by.

Howver, if you deal with larger animals, or places where cats can easily jump across your field of vision, you'll need some other technology, probably a camera and image processing.

Capacitive sensing might be another option for example using this info:http://www.smartec-sensors.com/assets/files/pdf/application_notes/APPUTI07.pdf . It's just a technological principle, I don't know how well it discerns between humans and animals.

Hi Anurag,

I am at a loss. 

I do not see how an ultrasonic sensor can reliably detect between human and animals any better than a PIR sensor.

The advantage of the PIR is that it can be set up to normalize the background IR in its field of view.

You could differentiate the amount of IR recieved, such as humans, children, large animals, and small animals, based upon the amount of IR detected.

I think it is time that you provide us with some diagrams of your idea and your discrimination needs for such a sensor.

Then we can better understand your problem and provide better answers.

Thanks,

DAB

As I mentioned before, any real work I did with ultrasonic doppler intuder detectors was a long time ago (before cheap micros). We had problems with false alarms from close up moths, distant curtains, moving air (drafts under doors etc). The move to PIR was mainly prompted by their improved performance at first (they only got really cheap later on).

If anurag is up for some serious research then he could use complex signal processing to try to use more of the huge amount of information in the ultrasonic signals but it would be new work and far from simple. (Classic doppler sensors only pull out  a speed signal - by modulating the transmissions you might be able to estimate speed and distance and size of the target) . I see that Aritech are still around and make hybrid ultrasonic/PIR detectors - they probably know what they are doing.

You could also think about enahnced PIR detectors (using a sensor array rather than just one sensor and segmented lens).

MK

Human motions have unique doppler signatures which reduces the possibility of false alarms.Acoustic doppler based human motion detection uses frequency shifts of low frequency ultrasonic tones to characterize motion.the basic concept used is when a continuous tone is incident on a person,the reflected signal contains a spectrum of frequencies arising from the doppler shifts of the carrier tone by moving body parts.these differences help in differentiating b/w humans and animals.

the system will comprise a ultrasonic transmitter and reciever to capture reflected signals.so , these are the details.

anurag gupta wrote:

 

,the reflected signal contains a spectrum of frequencies arising from the doppler shifts of the carrier tone by moving body parts.these differences help in differentiating b/w humans and animals.

 

Can you refer me to any references about this - only for fun because my real work no longer concerns intruder detection - and I'll think about the processing power needed to do it.

MK

Hi Anurag,

You have deffinately crossed into DSP territory.

To capture real time signals to process doppler is a non-trivial exercise.

Can you provide the source of your formulas?

Also, are you planning to use multiple detectors to get a spatial as well as signal map of the area being monitored?

I would have to see some study data before I would be convinced that such an arrangemet would be better than using a couple of PIR sensors coupled by some simple background subtraction algorithms.

You have your work cut out for you, but you have my interest to see how you plan to pull this off.

Thanks

DAB

How it is possible to detect the presence of human using pir sensor because the pir sensor can detect only the object at motion if there are human in a room in a stable state then how can we detect them? Another doubt is pir sensor produces 3volt digital pulse as output if it detects any object then how to differentiate between men and animals.i am working in this project please reply for my clarification. Thank you.

There are 44 replies here, they cover your question.

Sensor to detect Human Presence

There are 44 replies here, they cover your question.

Sensor to detect Human Presence