Stretch 0.5sec pulse to 6sec

[Michael A. Terrell]

amdx wrote:

On 2/25/2013 7:01 PM, Michael A. Terrell wrote:

amdx wrote:

On 2/25/2013 4:01 PM, Michael A. Terrell wrote:

amdx wrote:

How about this? My sensor points towards a part off a 2' x 3'
Aluminum plate, (part of a drain cover) I have people in a position
where I think they are out of the PIR site area, but they still cause an
alarm. Is a reflection possible off of the aluminum that wouls trigger a
PIR. This particular situation does not always happen, I have not pinned
it down as to sun position or temperature.
Or am I just wrong about where I think my PIR points?


How are they aimed? The center isn't the hot spot, you have to be
angled away so you can cause an imbalance in the two sensors. How wide
(in degrees) is your sensor?


I have the PIR site area limited by looking through a ~3/4" hole.
So I really can't tell you how wide the site area is. If it wasn't
raining I could do some testing and figure out the angle it sees.
But, I still wonder can IR reflect of a piece of aluminum?
That seems to happen on occasion.

Yes, it can, and that is why you need to be very careful to get the
maximum sensitivity where you need it. If it is outdoors, clouds
passing over can drive it nuts. Sometimes it's better to mount it where
it points down across the area you are interested in. Another way is a
video camera and motion sensing software. It is difficult to use PIR or
ultrasonic sensors in places with unstable environments. Another choice
would be a microwave motion sensor which are fairly immune to these
problems..

Ya, I limited it's area severely, I mounted it under a wide step so it
points at a concrete wall at an angle. The IR hits at about 4 feet away
to about 9 feet. The false alarms are not really a problem, sense it
triggered when the customer walked down the step, I'm outside waiting on
them while they move around and possibly retriggering the alarm.
The rain stopped so I did a short experiment and I don't think the IR
is hitting the aluminum panel.

So know I wonder can IR reflect off a concrete wall.

I haven't been able to cause a false trigger, but I know it has
happened, always seems to be when I have two or more people in the area.
It's a very minor annoyance, I'm just curious about the cause of the
problem.

I recently received a few of these PIR sensors,

http://www.mpja.com/PIR-Motion-Detector-Module-Mini/productinfo/19517%20SC/

I little testing and I could get my own answers.

The first PIR detectors I worked with were in the mid '70s. Some had
a set of lenses to let you select the pattern & angles. Have you
considered a modulated I.R. break beam across the path? Very low false
alarm rate and cheap to build. You can use a 555 to drive the emitter,
and a I.R. detector module from an old TV or other remote controlled
device. Add a couple tubes to reduce stray pick (Or simple lenses) and
place one piece on each side. The modules detect the beam and have a
logic output for data.

 

[Randy Day]

In article <9f6ae$512c181b$18ec6dd7$5028@KNOLOGY.NET>,
amdx@knologynotthis.net says...

[snip]

The rain stopped so I did a short experiment and I don't think the IR
is hitting the aluminum panel.

So know I wonder can IR reflect off a concrete wall.

I haven't been able to cause a false trigger, but I know it has
happened, always seems to be when I have two or more people in the area.

Could the rain have cooled the concrete (or the air) quickly
enough to trigger the sensor?

 

[Michael A. Terrell]

Randy Day wrote:

In article <9f6ae$512c181b$18ec6dd7$5028@KNOLOGY.NET>,
amdx@knologynotthis.net says...

[snip]

The rain stopped so I did a short experiment and I don't think the IR
is hitting the aluminum panel.

So know I wonder can IR reflect off a concrete wall.

I haven't been able to cause a false trigger, but I know it has
happened, always seems to be when I have two or more people in the area.

Could the rain have cooled the concrete (or the air) quickly
enough to trigger the sensor?

In Florida? That would result in lots of steam, which overloads the
sensors. The worst rains in Florida only last minutes, and make it
unbearable for an hour or so, till the humidity drops.