Is a simple cheap circuit possible that will detect the vibrations made by oncoming footsteps from a few meters away and trigger a relay at a preset trigger level ?

 

It all depends on the sensitivity you need.

If the material you are trying to "read" is a slab of concrete weighting 20 tons, and you want to detect a 103 pound girl walking on it in her socks, good luck.

If it was a 20 foot board with only 2 supports and you were trying to detect a 220 lb man in work boots.. That would be rather easy.

Look up seismometers.

They detect the vibrations caused by plate tectonics and other such events.

It sounds like you could make bad things. Dont hurt anyone.

 

@retched
Not sure why you think the OP is making BAD things.

@Curry67
If you can explain what the sensor is for and how you intend to use it, we could possibly figure something out for you, perhaps a motion sensor would work better, don't know...

iONic

 

Is a simple cheap circuit possible that will detect the vibrations made by oncoming footsteps from a few meters away and trigger a relay at a preset trigger level ?

I would guess that the large number of variables (surface walked on, shoes worn, gait and weight of walker) would make reliability and repeatability difficult. You might experiment with something like this.

 

What is the reason for using vibration rather than heat/motion?

I guess using some pins on a piezo, and an opamp to increase sensitivity would work for light vibrations.

 

I bought some seismic sensors for an alarm system a long time back.

Here is a document on design http://lib.semi.ac.cn:8080/tsh/dzzy/wsqk/SPIE/vol5071/5071-297.pdf

The ones I got were quite bulky, and rather heavy, and needed to be buried.

 

I was once calibrating a laser mounted on a concrete floor, and the spot began wobbling all over the screen. The wobble didn't change amplitude in a few seconds, so I decided It was not an earthquake. When I went outside to see what was happening, I saw a freight train passing by at about a quarter of a mile distance. This tells me that a laser might be used for a vibration detector.

 

Years ago I worked for Kistler Instruments. We buried a vibration transducer in the middle of the front yard of the building. We could tell when they were mowing the lawn, we could discriminate between girls wearing high heels and others wearing flat shoes walking inside the building.

 

... we could discriminate between girls wearing high heels and others wearing flat shoes walking inside the building.

What about mini skirt and trousers ....?


I have bought and built this, and it is working. Should be easy to implement a relay or something...

http://www.jameco.com/Jameco/PressRoom/recipe4.html

 

What about mini skirt and trousers ....?


I have bought and built this, and it is working. Should be easy to implement a relay or something...

http://www.jameco.com/Jameco/PressRoom/recipe4.html

It was a piezoelectric accelerometer that we buried. If we would have had to buy one, it would have cost far, far more than $1.95 though. Likewise the electronics would not have been cheap either. What cost $750 in 1968 to implement can be almost duplicated for 10 bucks today.

Karen was the only girl there worthy of a mini/micro skirt. Strangely enough, she was the receptionist. Trousers weren't a priority for us.