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.

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.