Momentary drop in sensor level

Apps
1

I am using Garadget in MQTT, non cloud setup with OpenHAB. Recently I’ve added a new rule that plays an alert sound as soon as the garage changed from “closed”. Funnily enough, every now and then (about 2-3 times a day), this alert sound would go off without anyone opening the garage door.

This was in my OpenHAB log:

22:18:01.597 [INFO ] [smarthome.event.ItemStateChangedEvent] - Garage_Status changed from closed to opening
22:18:01.608 [INFO ] [smarthome.event.ItemStateChangedEvent] - Garage_Reflection changed from 97 to 65
22:18:02.597 [INFO ] [smarthome.event.ItemStateChangedEvent] - Garage_Status changed from opening to closed
22:18:02.597 [INFO ] [smarthome.event.ItemStateChangedEvent] - Garage_Reflection changed from 65 to 97

So for about 1 second (which probably relates to the sensor scan interval), the reflection dropped from 97 to 65, and went back up to 97.

My threshold (srt) was set to 70.

Meanwhile I have reduced my threshold to 60 (pending further tests), and added a delay so my alert won’t go off unless the door is open for at least 3 seconds.

I don’t want to set my threshold too low, because I don’t want to end up in a situation where the garage door is open but registered as closed, and would rather err on the safe side.

I am curious though, as to what could’ve caused this brief drop in reflection. I wasn’t in the garage when it happened but at this point, we speculated that a gecko might have crossed the laser/reflector. However, I would think that a gecko would have produced a much lower reflection, which makes me wonder still.

Has anyone noticed this phenomenon?

2

The default/recommended threshold is 10. The only scenario when the threshold needs to be raised is when you receive false positive detection (e.g. reflective panels on the door, laser hits near objects etc).

3

I did have false positive detection initially with the default setting, which is why I had to dig around to find out how to increase the threshold. The question remains as to why it would drop like that every now and then.

4

This could be caused by insect blocking the laser/sensor or ambient light conditions.
If issue persists I’d suggest finding the lowest threshold where false positives are not an issue.