Wednesday, October 2, 2019

Homematic - Missing messages mess up metering

Well, actually they mess up diagrams, but this title sounds better 😅

My Homematic CCU2 collects data and displays them in a diagram. I had added an additional Temperature / Humidity sensor in the bathroom (for a future ventilation project) but sometimes an error was displayed, about some 'data missing'.


The cause

An incorrect factory default configuration. Duh.

Smart devices, and those a little more dumb 😎, have their own 'default' settings. Now if a manufacturer gets things right, everything should work right out of the box. Unfortunately, this doesn't always happen.

I couldn't find the cause of the problem, until I added yet another sensor for a little 'free cooling / freezing alert' function.

The old indoor sensor

I did install a Homematic IP humidity / temperature sensor in my bathroom. This one:


The idea is to switch the ventilation system to a higher mode whenever someone takes a shower. Typically taking a shower would also cause the local humidity to spike, so speeding up the ventilation system for, let's say, 15 minutes or so seems to be a good idea. It should bring humidity down just a little faster...

But before buying more parts and wiring up the the ventilation system (a WHR950) I'd better make sure the concepts worked.

Diagrams

I decided to create some graphs of the bathroom humidity and put them in a diagram. And that resulted in some weird behavior...

When I look at the graph I noticed there was often little bit of data missing at the end of the graph, like this:


The yellow line shows humidity as reported by the HmIP-STH, the red and blue lines are humidity as reported by the HM-TC-IT-WM-W-EU (regular Homematic wall thermostat).

I suspect what happens here is this: the software in the CCU is drawing a graph using b-spline or some similar algorithm, AND that the HmpIP-STH doesn't send any messages for a period of time if there were no changes (quite a sensible thing to do). See also the settings of the HmpIP-STH:


The 'leave 20 messages out' option seems to suggest that.

(Unfortunately, the Homematic stuff is great, but it's so focused on Germany that documentation is, ah, spotty. In fact, even the German documentation doesn't seem to explain everything, and the English is even worse. So I just have to guess the exact effect of each option.)


Missing data

Now, I think I'm experiencing a bug in the CCU firmware with diagrams and this missing data. I ask for a diagram for which there is partially no data. For example in the diagram below I have less than a months' data for all three sensors.

When this 'monthly view' includes data from the Homematic IP sensor HmIP-STH (which has been logged for the same period, but where some data might be missing) it shows an error message at the top of the diagram, like below. (It doesn't show that message for single day data.)


It won't show *any* data for the HmIP-STH sensor though it will show data for the other sensors. Zooming in proves there is data, it just isn't shown, see the first image.

I suspect that the CCU stumbles over a few bits of data missing at the start of the diagram, missing parts which are conveniently located to the left of the visible area when zoomed in.

Was my thinking wrong, or is this a bug?


The Fix

Fixed it.

I recently bought an outdoor sensor (to decide if I should open my windows, see here).

The new outdoor sensor:


Diagrams generated using the outdoor sensor did not cause the 'diagram problem'...

When I looked into the parameters, I noticed that both sensors had some completely different options, even if they serve pretty much the same purpose. But lo and behold, I spotted a difference...

The indoor sensor, default setting, had a different parameter:

Number of messages that are left out: 1.

The outdoor sensor, same option: 0.

I went back to the indoor sensor, and changed it to 0 as well. Problem solved.


It lives!

The proof of concept seems to work: I am able to switch on some LED's on the display unit in the kitchen, depending on the humidity in the bathroom.


I might even extend the system to support a ventilation boost whenever someone's cooking (not very useful, but fun) or reduce ventilation when no-one's home (that might save perhaps 0.3 kw x 5 hrs x 365 / 7 x 5 x 0.25 = 156 euro per year, enough to look into).

Anyway, my diagrams now show all relevant data, so it's time to start analyzing the bathroom diagrams and consider (re)wiring (to) the ventilation system.


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