Re: Ultrasonic Sensors

["rgondzur" <rgondzur@xxxxxxxxx>]

Whew!
After wading through all the "dialog", it's nice to get back to the
original discussion.
The actual area that I want to monitor is small.
For example, take a stake in the ground, attach a ten-foot rope and
walk a circle around the post. You have a circle with a ten-foot
radius.
Now replace the ten-foot rope with a twelve-foot rope and repeat the
process to create a concentric circle with a twelve-foot radius. The
difference between the two circles, two-foot of radius is the area that
I want to monitor. Anyone walking into the two-feet wide perimeter is
who I want to recognize. Consider it the demilitarized zone around the
inner circle.
In my original posting, I mentioned the parking sensor system on a BMW
auto. It indicates when someone approaches the car and gets within two
or three feet of it. The car is replaced by my inner circle, the area I
want to protect.
The catch is, people are allowed to walk through the outer circle and
into the inner circle. Therefore, the sensors can't hinder their
progress. I just need to know when have approached the inner circle by
passing through the demilitarized zone.
I believe the BMW uses ultrasonic sensors with a moderately focused
beam, but I don't know that for a fact. However they are sensing
objects, it is a fairly solid system with few false alarms.
I originally was thinking of using wireless motes interfacing with the
sensors to form a mesh network, but rethinking the process will allow
for wired sensors. That will help with power consumption of the sensors
themsselves and simplify the controller monitoring the sensors..

One final issue is that it won't always be a nicely-formed circle. They
can have odd shapes, kidney, oblong, ... so there positioning of the
sensors to achieve overlap around the perimeter will vary.

If I can find a reliable sensor like the auto uses, I'll be in
business.