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We've had our house equipped with KNX bus cables. Only now have I discovered Wago and figured out non-KNX systems are much cheaper. We need KNX 11 switches, for that we pay more than €2000. So we have the bus cables installed and I've been looking for alternative bus systems but found nothing. The only thing I've come up with is to build switches myself. Each switch would be equipped with a ATMega8 and a P82B715 I2C extender and some resistors. One switch would cost about €40 in parts compared to €190 for a KNX switch. The bus cable would be connected to another ATMega8 (the I2C master) that would control 11 relays. These relays would be connected to the Wago digital input module. This master module would cost about €30 in parts. So my questions are:
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Hi, Let me add that I don't think I2C is a suitable bus system for this kind of solution, as it is designed to allow a total bus capacitance of 400pF, which translates in having only a few meters maximum distance, which in turn is not practical for home automation. However, there are nowadays manufacturers in the markets that can provide you with fully certified KNX coupling modules and stacks, for you to use with your favorite microcontroller. This should allow you to build a DIY KNX system. You can take a look to these two manufacturers, although may be others: Hope this helps. Regards, Asier |
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The simpliest binary input 2-fold to the KNX system costs about 50EU. You can mount it with standard switches (recomended pushbutton). But if you build your own switch, you will get priceless satisfaction :-) What do you want to control? Heating also? |
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In addition to Tommy' anwser I can also suggest Theben's TA6 KNX ( see http://www.theben.de/en/Products/SYSTEMS/KNX/TA-6-KNX ).This allows you to conect 6 conventional push buttons. It is a cheaper alternative to pure KNX switches ( round about 130.00 Euros ) but you still get the beneficts of a KNX system. Or you can also connect the conventionl push buttons via the KNX bus cable directly to the binary inputs of a Zennio ACTinBOX CLASSIC HYBRID (Multifunction Actuator 4Outputs 10A 6Inputs) at round about 180 plus VAT. Or you can even think about chinese KNX manufactures that are now starting to arise. Look for example at http://www.video-star.com.cn/index.php?option=com_k2&view=itemlist&layout=category&task=category&id=27&Itemid=19&lang=en. Not sure about the prices in this case. |
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I think you should find a way to use KNX, building something yourself is potentially a false economy in the longer term, due to maintenance costs, and potential other issues (e.g. if your custom solution causes your property to burn down, you may find the insurance will try to not cover it, or if you try to sell or rent your property, purchasers may be concerned [and try to negotiate a discount] that there is something so non-standard in place). |
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I don't know how it is in your country, but I had to use KNX after evaluating various other solutions (including DIY) because here in Italy electrical components MUST be certified, and KNX system seems to be the only "completely" certified one. I'm against such policies, but I must admit that playing with 6kw @ 220v may be dangerous at least, and I don't have a full lab to test a DIY solution properly to make it safe. This sucks, but it's the reason I'm using KNX and not crafting a DIY solution, despite how much I'd love to. |
