Hardware advice - Interface Hardware

I’d appreciate some advice in relation to hardware.

I’m planning to add to my existing OpenHAB setup and need to use Homegear to control some wireless TRVs (Thermostatic Radiator Valves) and also connect to some wireless smoke alarms.

So I need my solution to work with HomeMatic smoke detector (HM-Sec-SD)

Then in relation to TRVs I have two choices (I think), the “HomeMatic Wireless Radiator Thermostat (HM-CC-RT-DN-(BoM))” or one of the various “MAX! Radiator Thermostat” devices.

My queries are two-fold:

Firstly if I want to control both HomeMatic & MAX! devices what is the best interface hardware to use (and would I need two of them).

Also in relation to the HomeMatic vs MAX! TRVs what are the pros-cons of each (I was looking at the MAX! range because they seem to be more readily available in the UK).


I would buy a CUL USB stick - it’s easy to use and works really good - much better than the communication modules from eQ-3. But you need two of them indeed, if you want to use HomeMatic and MAX!, as the register settings are different. One disadvantage is that AES handshakes are not supported yet. For them to work you need one of the eQ-3 devices.

I don’t know what the prices are in the UK, but in Germany HomeMatic is not much more expensive than MAX! (ok, except for the really cheap new BC-RT-TRX-CyN (TRV basic) ), so here to me it doesn’t make much sense to buy MAX! devices. HomeMatic works better than MAX!:
[li] You don’t run into the 1% limit that easily[/li]
[li] As you can disable wake on radio, the battery life is better (especially when the total number of devices increases)[/li]
[li] The HomeMatic devices seem more robust and my guess is the mechanical system is better.[/li]
[li] The temperature regulation might be better (I don’t know for sure)[/li][/ul]



Thanks for your thoughts.

In relation to the HomeMatic wireless TRVs which ones do you have.

These are the only ones I can find in the UK:

conrad-electronic.co.uk/ce/e … 5?ref=list

But I’m not sure if this is compatible with Homegear, the only part I can see in the compatibility list is this part: HM-CC-RT-DN-(BoM)


yes, that TRV is the HM-CC-RT-DN and it is compatible to Homegear. I’m using it myself :wink:.



Ah good, thanks.

I must admit I’m finding it pretty difficult to work out which of the wireless TRVs are compatible.

These are the ones I’ve found to date (available in the UK) but I’m not sure which work with Homegear:

EAN: 4047976420162
conrad-electronic.co.uk/ce/e … ostat-head £16.99

EAN: 4047976990177
conrad-electronic.co.uk/ce/e … ostat-head £22.99
rapidonline.com/Electrical-P … at-52-1975 £21.21+VAT

EAN: 4047976059362
conrad-electronic.co.uk/ce/e … ostat-head £28.99

EAN: 4047976308095
rapidonline.com/Electrical-P … ve-59-2090 £11.79+VAT

EAN : 4016138939255
rapidonline.com/Electrical-P … -C-60-4094 £25.34+VAT (set of 3)

What are your thoughts.

[li] EAN: 4047976420162 => works[/li]
[li] EAN: 4047976990177 => works[/li]
[li] EAN: 4047976059362 => works after modifying the XML file (contact me, when you want to buy this one, it’s just adding a number)[/li]
[li] EAN: 4047976308095 => has no communication interface[/li]
[li] EAN: 4016138939255 => also has no communication interface[/li][/ul]



Excellent thanks.

By the way, what is the “You don’t run into the 1% limit that easily” you mentioned in an earlier post.

868 MHz devices are only allowed to transmit 1% of the time. Typically the 1% is measured per hour, so devices have to limit their transmissions to 36 seconds per hour. Id’s say the average packet has a length of 13 bytes. With these packets at 1kb/s one packet needs about 100 ms to transmit (it’s actually a little more because the rf chip adds some more bytes, but at least the culfw does not count that). So you can send about 360 packets per hour. Some HomeMatic devices support a mode called “wake on radio”. This mode enables battery powered devices to always be reachable with a reasonable battery drain. HomeMatic wake on radio packets have a preamble signal sent 360 ms prior to the packet. So one packet now needs 460 ms to transmit resulting in 78 wake on radio packets per hour. Luckily wake on radio is implemented well with HomeMatic so there is only one wake on radio packet per communication queue. So you normally don’t run into any problems. With MAX! the preamble signal is sent 1000 ms prior to the packet resulting in 33 packets per hour. Additionally most of the packets (even within one queue) are wake on radio packets. That’s the problem. For the central it’s a big one - 33 packets is not much. But even for devices it’s not a lot. After opening and closing your door 17 times in one hour, the door contact is not working anymore…



Thanks for the detailed explanation. Cheers