Ultrasonic sensing

Thread Starter


Joined Nov 13, 2018
Hi all,

I am working on an ultrasonic sensor for occupancy sensing. This device would drive an LED based on movement, and I was wondering if detection could be achieved the following way

Where the sensors and the moving person lie in opposite sides of the wall, and the ultrasonic waves would ultimately travel from the moving person onto the Ultrasonic receiver for processing.

Has anyone heard of this or implemented it? I just want to know if it is possible with any low grade transducer.


Joined Jun 4, 2014
What would stop the ultrasound going from the TX, bouncing off the wall directly opposite and back to the RX? The distance is shorter and the area reflecting is bigger so this is going to be the bigger signal.

Deleted member 115935

Joined Dec 31, 1969
It depends if you want to detect the presence, or where the presence is,

If you flood an area with a fixed signal, if nothing is changing , you get a fixed response back.
any movement that changes the return, changes that response.

Looking at this as a radio wave, if you mixed the transmitted with the received, the difference signal would be constant with no movement, and change with movement.

Now the tricky bit where it all falls down.

The change due to movement is going to me very small compared to the standing , its going to be none specific, and your going to get variations even in a fixed environment, due to things like air movements, noise etc.

How you discriminate real movement against the background is the nub of the question,

Over the horizon radar and submarine sonar have the same problem,
very little real signal and lots of none wanted signal.

waterfall display is there friend,
but that could be way over the top for your application,