The challenge of standing in the toilet in the dark

The Zennio Motion Detector (ZN1IO-DETEC-P) which also includes a luminosity sensor connects to devices such as a TMD Plus 4 via a pair of wires and not directly to the KNX bus. In such a case it's the responsibility of the TMD to place the messages onto the KNX bus and not the Motion Sensor. This process (as I found) is less than perfect. The main issue I found appeared to relate to some of the limits with the communication between the Motion Sensor and the TMD and these are not really clearly explained in the Zennio manuals. Here I go into some of the issues I experienced and what I discovered.

The Zennio documentation relating to the communication between the Motion Sensor and (in my case) the TMD states that we should: "bear in mind that during continuous motion detection, the value of the luminosity level may take a little more time to update, as both signals (detection and luminosity) share the same input port of the device." From my testing it appears that what can occur is that if a the motion sensor is busy sending motion occurrence events the luminosity status is not sent. Exactly what signal (digital or analogue) is used to communicate motion and luminosity status to the TMD is not explained. However, it appears that the Motion Sensor itself is pretty dumb and what it sends is pretty simple.

As a result of this - one of the tests I initially tried to get working behaved strangely. What I wanted to occur - was in a toilet with a motion sensor and no light switch - was to have the light to come on only when there was low light AND motion. It appears that there are settings to achieve this in the Parameters for the TMD (which I'll discuss below). In actuality I was more interested in getting this to work in some other spaces (e.g. the garage). However, for testing purposes it was simpler to trial this in the toilet where I could easily control the light by opening and closing the toilet door and subsequently control the light. I placed settings so that if the toilet door was open there was enough light such that a Motion sensing event would not be triggered - and this worked ok - so far so good. When the toilet door was shut luminosity dropped beneath the level necessary to trigger a motion event and as such the light should have come on. However, this is where I ended up standing in the toilet in the dark. I believe the reason was as follows. While the light level had dropped to a point where the light should have come on, the Motion Sensor become tied up continually reporting motion that was sensed and didn't have the bandwidth to report the light level to the TMD. So as I tried to move around in the toilet in the dark to get that motion sensor working - this only made the situation worse as the Sensor remained fully occupied sending motion sensor data continuously, with no time to update the luminosity. In the mean time the TMD remained unaware that the luminosity was now 0% with the door closed. Interestingly when I stopped moving and remained still in the toilet, the motion sensor was able to update the luminosity to the TMD and this provided the opportunity for the lights to come on. It seemed counter intuitive at the time because the lights appeared to come on when there was no motion.

Probably the big frustration in all this, besides it not being well explained in Zennio documentation (that I could locate), was that when I tried to monitor what was happening I didn't initially realise that the luminosity the TMD reports is not what it actually may be. So when I set the TMD to report luminosity every 20 seconds, if the TMD didn't receive updated data from the Motion detector, it appears to send what it knew to be the case previously which, for reasons just described, may no longer be correct.

So the outcome of all this - is that I don't believe the Motion sensor can't really support what I was trying to do. If light levels drop suddenly (i.e. from a toilet door closing) then this can't be communicated quickly if the motion sensor is busy reporting motion. However, where light levels change more gradually and in the absence of continual motion then it's more likely use can be made of this functionality. Hence implementing this functionality in spaces like my garage should work reasonably. Anyway, after a long explanation of what didn't work here's details on what should work.