Accelerometer on doors and windows

Question

We have made a mistake. We created this pcb with accelerometer , a very good one (ADXL345) datasheet here and it sleeps ,and waking up on acceleration event. in our case we set it to almost the minimum possible of 124mg thresh .

What happens is that it works great almost for any touch or move that you apply to it by hands, means if its on a table even a tiny move will fire it on .

But, when its mounted to a door, or window, if you open the door not quickly enough it just won't wake up .

We have tried everything, including taking sensitivity to maximum.

Seems that it only needs a change that is not occur on an average door opening .

1. Is there anything you can do to improve this not including migrating to other sensors ?

2. We have a free GPIO connected to interrupt, we can add some part there, that will sense this tiny movement, is there anything like tilt sensor that will do it?

Thanks .

Answer 1

The first thing to do is to mount the accelerometer as far out on the swinging end (not the hinge end) of the door as possible. Then, of course, the accelerometer axis must be aligned perpendicular to the door.

High pass filtering may help, but that requires leaving power on.

Ultimately, you may not be able to do get what you want within the constraints you have imposed on yourself. The obvious answer is to use a device appropriate for this application. Not all things are possible just because you can write a spec for them.

"I bought a bushel of tomatoes instead of a lug wrench, and now I'm on the side of the road with a flat tire. How do I use these tomatoes to get the tire off. No, I insist on not walking to the hardware store around the corner to get a lug wrench."