Last week I attached some 1-Wire temperature sensors to the floor heating tubes to monitor flow- and return temperatures. While I was doing that, I looked at my Remeha Calenta again and thought what a pity it was that I failed to monitor the Calenta with the Remeha Gateway. I’ve known for a long time that there’s a 2nd solution to this: Remeha Recom. A “special cable” and the Recom software make it possible to monitor your Remeha Avanta, Quinta, Calenta (and more). However the price for this cable is rather high; you won’t be able to get it below 130 Euros with as only result a Recom window on your screen where you can see all kinds of things being monitored… all you can do is make a screen-dump or log the values to a file… 🙁
And if I would buy that “wonder cable”, would I be able to understand the protocol? I didn’t want to risk the chance of buying that expensive cable and not coming any further than using Recom, so i stopped thinking about it. Untill last week.
I started roaming the Internet for more information; I read about “it” being a null modem cable; I looked at the PCB and saw the RJ-11 connector for the Remeha cable was labeled RS-232; I took a long cable with a RJ-11 plug and stuck it into the connector and started measuring with a voltmeter; I saw the outer 2 were 5V and the other GND; that leaves the inner 2 for the serial part. I started thinking about what this super duper Remeha cable could hide inside to make serial communication work? There has to be something special to it… converting TTL to RS-232 perhaps? Why not give it a try…
I have a MAX3232CPE laying around for some time; so I planted it on a breadboard, added some 0.1 μF capacitors and built this schema I found (click it):
Here’s the result:
Guess what… it works!! My Remeha Calenta was recognized immediately and I watched the data arriving in Recom:
With no more than 8 Euros I created my own interface cable; too ridiculous… Special cable? My A!@&%#%^!!!
OK, but this was just the beginning. With a serial port sniffer i saw the Calenta being queried and I started recognizing the flow temperature, return temperature etc. in the responses that came back from the Calenta. These packets look like this:
02 01 FE 06 48 02 01 F0 14 AA 14 00 80 00 80 86 F3 00 80 B7 10 00 80 40 1F 70 17 00 80 00 00 00 00 00 BC 02 00 00 00 00 64 00 00 00 00 C2 0B 10 00 FF FF 00 00 00 00 FF FF 17 00 BC 02 00 00 00 00 00 00 00 00 00 00 00 C5 9B 03
After an hour or so, i knew where to find some temperature values and stuff like that. The F0 14 marked in red for example, means 53.60 degrees Celsius. That was easy… not good enough for a quiz 🙂 But I also saw on the amount of values Recom could produce from the incoming bytes, some things had to be stored in bits; the on/off, yes/no, open/closed values appeared not to be stored in a byte, but ‘hidden’ somewhere in a bit maybe? Hmm, how do I know exactly when the Gas valve opens or closes, so how I can locate the bit for that? If it is stored in a bit? This could become a bit more challenging and time consuming than I would like.
Aha! There’s a config directory belonging to the Recom software package, containing XML files; one of them was named exactly like the model that Recom detected. Let’s have a look inside that file… Bingo! These XML files contain very detailed information; they tell me that I can find that Gas valve value in bit 0 of byte 38… Yeeha!
Now it’s just a matter of finding out some more about the leading and trailing bytes and I can start creating my own Remeha Calenta interface to my Domotica system.
Finally I’ll know what the Gas is being used for: DHW or heating. And when the water pressure drops below a value I find alarming, I can be warned before it’s too late. And I can see how much power is actually being produced; and …
Update: RJ-11 is incorrect; it’s a 4P4C connector!