If you want to measure just a few environment value and send them to a central server, the ESP8266 is a great platform. And it is even cooler when I tell you that you can do it without even programming. Check out the ESP Easy firmware. This firmware allows to configure sensors and actuators connected to the ESP8266 without the need to write your own program. You can just configure the sensors in the web interface:
If you are an experienced electronics hacker and you want to do some tests with KNX, you need to invest a bit. However, a minimal KNX setup for initial tests doesn’t have to be very expensive:
- a 29V power supply that supplies at least 300mA
Most bench power supplies will do the job. For a test you don’t have to buy an expensive KNX power supply.
- a KNX choke
You can’t connect KNX devices directly to the power supply. A choke is essential. Without it, no communication on the bus will be possible. Standalone chokes starts at around 35€.
Another option is using a 47-Ohm resistor in between the power supply and your KNX bus line. While it might not work, it is worth a try as it will cost you only a few cent.
- a KNX sensor
If you have some push buttons laying around, a cheap KNX bus coupler from eBay might be the cheapest option. You can get these for less than 30€
- a KNX actuator
Some KNX sensors (like wall-mounted push buttons) have status LEDs that can be controlled from the KNX bus. In this case, you do not need a separate actuator. Otherwise have a look on eBay for old binary outputs. You should be able to find something for less than 30€
- USB or Ethernet interface
USB interfaces are usually a bit cheaper. You might find used USB interfaces in the range of 50-80€. However, I would still recommend to spend a bit more money and buy an Ethernet/KNX interface. You are more flexible with these as multiple devices can access it simultaneously. You might not be able to save a lot of money on a used one, but new Ethernet interfaces are available from 150€
This means, a minimal KNX setup will cost you between 200€ and 300€. This isn’t really cheap, but still less expensive than many people might think. The good thing: The most expensive component is the Ethernet interface. If you decide not to go on with a full KNX installation, you can still sell it for a good price. Otherwise, you can use this in your house installation.
The minimal installation looks like this: