On Wed, 15 Jul 2015 13:11:27 -0700, mike wrote:

On 7/15/2015 8:45 AM, wrote:
On Tue, 14 Jul 2015 17:26:31 -0700, mike wrote:

On 7/14/2015 4:12 PM, wrote:
I bought today a "hands free" garbage can for the kitchen. It said on
the box that it has a motion detector for hands free operation. The
unit as a whole is well made and has features I like. The problem is
that when slid under the counter the motion detector detects the
underside of the counter and the lid opens and stays open. So it must
detect reflected IR, whether moving or not. The under counter position
is where it must go. The hands free opening is why I bought it, it is
for use in the kitchen. All the electronics are in the top, which
comes off in order to remove the garbage receptacle. So I need some
sort of sheet IR absorber so that the thing will work properly under
the counter. I can operate it manually but I don't want to touch the
garbage can when I'm cooking and have food of one sort or another
stuck to my fingers. Anybody have any ideas? I thought about maybe
taking the thing apart and putting a mirror inside that would make the
sensor see at an angle so that it wouldn't detect the underside of the
countertop but then it might open when someone walks past. So it looks
like what I really is a good IR absorbing material that I can fasten
somehow to the countertop underside. Any suggestions?
Thanks,
Eric

Get out your digital camera and take a look to see where the light
comes out and the pattern on the underside of the counter.
You may be able to mask the light source.
You can use the camera to look at reflectivity of various surfaces.
The TV remote makes a usable source of infrared.

The camera is not very sensitive in the infrared, but often good
enough to do the job.
That's a great idea Mike. I have a digital camera I modified to see
only NIR so it should great. Then I can maybe use black paper like Dan
suggested.
Eric

I still think you're attacking the wrong end of the problem.
If you can mask or reflect right at the source, you won't need
any absorber.
I have a motion detector light that was always triggering when I
didn't want.
I put some black tape along the side of the emitter to restrict the
angle (field of view). Worked great.

I'm still confused about why it matters what reflects as long as it isn't
moving.
Typical PIR projects multiple images onto the sensor.
It triggers when there's amplitude modulation produced by changing
patterns as something moves in range.
Even though the thing says it is motion activated I think it just
detects its own reflected light because when the garbage can is slid
under the counter the lid opens and stays open. No motion required. So
I think it does not have a PIR detector but instead sends out pulsed
IR and when it is reflected back the lid opens. Just holding my hand
over it will cause the lid to open and stay open.
Eric