KNX Tips And Tricks Part 1: VMWare, Dongles, and Scene Teach-In

The Back Story

I want to deploy KNX in some existing and new buildings. KNX is something I’ve been interested in learning ‘how to do’ for ages. Finally a good intersection of time and opportunity has lead to this being the right time for me to undertake the learning journey.

In the COVID era, I couldn’t easily attend the hands-on physical accreditation training courses in KNX design and deployment that are offered by the very fine people at IvoryEgg. So, instead, I started with a free KNX intro seminar they delivered online..

Next, I did the short online ‘eCampus’ introductory course at the site to get a high level understanding of how to drive the ETS5 app (and I will say that it was indeed very useful for that purpose).

Following that, well, I just licensed ETS5, bought some KNX gadgets from IvoryEgg, and started to just ‘figure it out myself’ because, to borrow the classic geek thought bubble:

How hard can this be?

The answer is that its not too hard, really, except that in doing it this way I’ve missed out on plethora of small nuances (especially about how to drive ETS5, and in how KNX concepts map to ETS5 reality).

These pieces of missing knowledge and understanding would have been gained by doing a formal hands-on training course. Without that, I found myself repeatedly in the situation of knowing something can be done in ETS5/KNX, but being unable to figure out in the first instance how to do it.

I felt that there may be some merit, for others, in writing down the non-obvious things – and their solutions – as I go along. Hence this blog post (and any others that may follow).

What is KNX?

KNX is a remarkable thing. It is a 30+ year old, published and standardised, protocol for building automation. It includes a standardised set of mechanisms for physically wiring and installing KNX-speaking devices in a building. More than 450 hardware vendors with guaranteed interoperation.

There is one ‘master’ programming tool (“ETS5”) that is used to program/configure and deploy KNX devices in real world environments. It imports definition databases and applets from each manufacturer, on demand, to support the myriad variations offered by each device, in a (moderately) consistent manner.

Now, lets start looking at the tricks and traps I have encountered on my self-taught journey into the wonderful world of KNX and ETS5:

Using ETS5 on a Mac: Making it work with VMWare Fusion

ETS5 is Windows software. I use a Mac.

I am running ETS5 on Windows 10 by using VMWare Fusion, which turns the Windows environment into a window on my Mac. This works really nicely with one particularly frustrating and non-obvious trap, related to ‘Network Settings’.

Out of the box, VMWare Fusion configures the Windows virtual “Network Adaptor” using NAT. This means that your windows instance has no direct TCP/IP connection to your Mac, but rather that it is sharing the IP address that your MacOS system uses.

Far from being a good thing – with ETS5 this is a very bad thing.

That’s because ETS5 relies on being on the same physical LAN segment as any IP-connected KNX devices (KNX ‘Interfaces’) that you want to use.

If you leave the VMWare environment set up using VMWare’s internal NAT then ETS5 cannot ‘see’ any of your TCP/IP-based KNX access devices at all – it is as if they just don’t exist.

You can’t make them turn up on the ETS5 interface selection page.. nothing works. Even worse, there are no error messages to help you figure out what is going on, either.. its just that nothing works as expected. 

Fortunately, the solution is simple.

In VMWare fusion, go to the Network Adaptor settings for the Windows instance, and change it to use ‘Bridged (Autodetect)’ instead.

That is all there is to it! Now your Windows instance reaches out and obtains its own TCP/IP address on the LAN, and it now has distinct (and direct) network identity. Now, it can see the LAN environment properly including (in particular) the IP Multicast packets that KNX relies upon, to work properly.

Fire up your ETS5 software again, and now all your KNX interface devices magically autodetect and work as expected. Win!

The only other thing of operational consequence in terms of using VMWare Fusion to run the Windows instance you need is that you need to plug the ETS5 license dongle into the Mac after activating my windows instance in VMWare Fusion, or it doesn’t ‘see’ it in ETS.

At worst (or if you forget), just unplug and re-plug the device after launching ETS5, and ETS5 will re-scan and notice the device soon afterward (no need to quit/relaunch ETS5).

How to avoid losing the (tiny) dongle

The ETS license is implemented via a physical USB Dongle. I have some issues with that dongle.

Iit is tiny, the same size as those little plug-in wireless keyboard dongles. This is something I hate – because a software license worth thousands of dollars shouldn’t be deployed in something that is so very easy to lose!

(Note that if you do lose the dongle, you can get it replaced for a moderate re-issue fee – but – why make it so easy to lose the thing and suffer financial cost and replacement delay in the first place?)

The ETS dongle uses a conventional USB-B plug, and my Mac is 100% USB-C. Given how expensive the license (and hence dongle) is, I have no qualms about dedicating an Apple USB-B to USB-C adaptor for the exclusive use of the dongle.

Because of that, though, I can’t leave it plugged in to my Mac all the time.

When you license ETS5, the KNX association sends your dongle in a lovely little presentation box. The box is made of sturdy cardboard material with nice printing on it, and the dongle sits inside, in a little foam bed. Very swish.

This box is big enough that I can put it in the accessory pouch in my laptop bag without losing it. Having to open that presentation box and clip the dongle into the Apple USB-C adaptor to use it, and then having to take it all apart again after each use, was painful. I lived in fear of the dongle getting detached from the adaptor and being lost.

This lead me to a pragmatic solution to the issue of the thing being too small.

What I did was to cut out a little hole in the end of the cardboard presentation box, plugged the dongle into the USB-C adaptor, closed that into the box and taped it shut (and wrote my name and number on the back).

In effect, I have created my own ‘super size’ and natively USB-C version of the ETS dongle, that is much harder to lose! This makes it much, much easier to find (and harder to lose down a drain) versus dealing with a little green dongle the size of a coffee bean.

Make a test bench to play with

It is very worthwhile getting a selection of real KNX devices as soon as you can, and starting to play. Here’s a photo of my home test bench at an early stage of my own exploration’:


What I did soon afterwards was to segment my KNX environment between that test bench and some pre-existing KNX equipment that was installed into my house some years ago by someone else (to implement an underfloor heating system). I segmented it using KNX/IP routers (more about those in a later blog post).

This means my test bench can be turned off and on, or futzed with in general, without breaking the production environment in the house. However, because I am using a couple of KNX/IP routers (one in the production setup, and one on the test bench), I can still reach back and forth between the deployed hardware and the test bench to try things (e.g. making a switch on my test bench drive a real world gadget somewhere else in the house).

Understanding ‘Scenes’

Scenes are an excellent concept in KNX – and it seems to me that driving rooms (and outcomes) via scenes is much more rational than having a forest of individual light switches and/or dimmers, even if all you are adjusting is lighting.

That said, once you realise a scene can drive outcomes across multiple types of actuators at once (lights, climate control, blinds, locks, audio systems, you name it)…that is the real lightbulb moment, starting as simply as the notion of having one button at the building exit labelled ‘Home/Away’.

There’s a key (and quite useful) concept related to scenes, called “Teach-In”. More about that later.

The ETS menu structure device Parameter configuration and adjustment is highly dynamic – sub-menus come and go depending on other menu selections

The Theben TA x S binary input device (you can buy them in various values of ‘x’, e.g. 2 4, 6 or 8) is a great device.

This was the first device I tried to get the hang of configuring using ETS5. When I started trying to do that, I just could not work out how to send anything but binary (single bit on/off) outcomes from it.

What I really wanted to do was to make a row of buttons that are ‘scene selection’ buttons. I made up a nice metal box with a row of pushbuttons on it, I wired them into a TA 4 S unit, and I set out to make each button select a scene number (1 through 4).

In the first instance, when I tried to program it in ETS5 – moving to the “Parameters” tab for the device – I just could not work out how to send a scene number with this device.

“Out of the box” the unit let me drive the switches as binary devices (one bit per input) only. It has lots of flexibility about how that works (in terms of whether the bit sent represents absolute switch position or a toggling value, various de-bouncing parameters, etc etc). All lovely, but I wanted to send scene numbers, and they were just absent from the menu structure entirely.

Finally I figured out the subtle quirk (in my view) of the ETS5 interface, and it is this:

When you are looking at a Parameter menu for a device, take note of whether there is a ‘+’ or a ‘-‘ to the left of the menu concerned. If it is a ‘+’ then there is a hidden sub-menu, waiting for you to discover it, by double-clicking on the menu concerned.

In my case, realising that and opening the button menu revealed a sub-menu that let me chose the type of data to be sent in response to input changes. Yay!

This situation can continue through multiple levels…there can be rabbit holes within rabbit holes.

I discovered yet more sub-menus allowing me to configure other cool things to do with that TA 4 S device.

The crux, then, is that there is a pandora’s box in the Parameter system, and you just need to know to look for it. Changing parameter settings can bring additional sub-menus dynamically into existence related to the thing you just changed… its an exploratory process, and once you know how to open the door to deeper levels… keep doing it!

WIth that successful discovery made, I programmed my button box to send scene numbers 1, 2, 3 and 4 in group telegrams in response to pressing buttons 1,2, 3 and 4. I downloaded the configuration into my devices and started pressing buttons… and … weird stuff happened (!).

This lead me (after significant head-scratching) to the next discovery:

Scene Numbers officially start at 1 but they have an underlying Index Origin of 0

If your device supports setting or recognising Scenes using the data type ‘Scene’, then you have 64 scenes to choose from, numbered 1 through 64.

However, ‘under the hood’, the Scene numbering that is actually sent ‘on the wire’ is a value from 0 to 63.

This means ‘Scene 1’ is actually sent as an unsigned 8 bit value of ‘0’, Scene 2 is sent as a value of ‘1’, and so on.

The source of confusion here is that some devices (like the Theben TA x S units) don’t seem to allow you to send a ‘Scene number’ as a data type (if you can, I haven’t found it yet). They do let you send a “Value” perfectly happily though (as an 8 bit unsigned byte).

Devices that receive scene numbers and that describe them as a Scene then operate on the byte received as a value you describe starting from 1. Hence when configuring an actuator to respond to, say, Scene 4, you select “Scene 4″…and that scene activates when a ‘3’ comes in over the wire.

Understanding this, at last, I reprogrammed my TA 4 S to send ‘Value’ bytes of 0, 1, 2 and 3 for my four buttons. When my group telegram packets then landed on the actuators I had configured to respond to Scenes 1, 2, 3 and 4… the right thing started to happen at last.


I expect this could also be fixed by tweaking the data type for the TA 4 S unit in the ETS5 setup for device, to make sure the TA 4 S ‘knows’ that what is being sent is a scene (and thus to avoid this confusion). In the end it doesn’t matter, providing you understand the underlying issue.

What the heck is “Teach-In”?

Teach-in is a pretty cool concept, but some Googling on my part failed to turn up a good explanation of what that really meant in practice. Various KNX product data sheets mention that their Scene logic supports Teach-In, but they mention it as if it is an axiomatically understood concept for the reader. Well, it wasn’t at all obvious to me.

One way to think about Teach-In is as if Scene numbers are ( in my case, literally) a row of numbered buttons on a button box. A way to think about that row of buttons is to compare to them to the row of ‘station selection’ buttons on an old-style car radio. Just hit a button to recall a previously saved radio station frequency, to save manually adjusting until you bump into it.

To continue the car radio analogy – if you want to set up one of those channel buttons to select a station, you first tune in the station manually, and then you press-and-hold the button concerned for a few seconds, which locks the current station in to the button you are pressing right now. In other words, long-press means ‘save station here’.

Teach-in, it turns out, is the analogous thing in KNX!

Teach-in is the way to update (save) the current actuator settings back into a scene number in those actuators ‘on the fly’. This can be far better than statically programming them in ETS5 and hoping that they somehow come out ‘perfect’ in your real-world building (and that the occupants’ needs won’t evolve over time).

If your actuator(s) support Teach-In, then this is how Teach-In works:

– Adjust settings on various actuators in some way other than via scene change. This might be by using manual control buttons on the actuator (if present), and/or by using other KNX sensors to individually change settings, and/or using a KNX whole-of-building control panel or a app to adjust individual lights, sounds, blinds, whatever to be ‘just how you want them’

– Once you have your room and/or entire building ‘just the way you like it, you can save this entire setup into a Scene number across all the relevant actuators by sending a group telegram to those actuators containing the scene number plus 128 (i.e. with binary bit 7 in the byte ‘set’).

Hence to update (re-save) the current actuator configurations into Scene number 6, you would send a group telegram specifying Scene number 6+128=134 (or if sending Values, that would be 5+128=133) to the Scene selection element of the actuators concerned. Bingo – you’ve saved your current Scene state away for future use!

Once I understood this, some nice features back on the Theben TA 4 S suddenly made sense:

By opening up yet more of those hidden sub-menus in the Parameters section for the TA 4 S, it turns out that you can program each single button to be able to send three distinct Value numbers based on ‘how’ you press the button!

You can send distinct Values out on each button depending on whether you (1) short-press the button; (2) long-press the button (i.e. press-and-hold), or (3) double-tap the button

Understanding this, back on my test bench, here is what I did to prove it up:

I programmed the TA 4 S in my button box to send 0, 1, 2, and 3 in group telegrams to my actuators, for short presses of buttons 1,2,3 and 4 (Scenes 1 to 4)

I programmed it to send the values 127, 128, 129, and 130 in response to a long press (Scenes 1 to 4, plus 128)

I also programmed all four inputs to send the value 6 (i.e. select Scene 5) in response to a double-tap on any of those inputs. I programmed Scene 5 in all of my actuators to mean ‘turn everything off’.

And voila – a nice demonstration of Teach-In:

– Press a button to select a scene.

– Adjust manually by other means, and then press-and-hold any button to store the current actuator settings back into that button (car-radio style) – nifty!

– Double-tap any button to turn everything off (Scene 5) – just to demonstrate an outcome for that third way to use the very same buttons.

Next Time

In the next Part, I’ll discuss some tricks and traps around the selection/purchase and programming of KNX/IP routers (and what is, and is not, a ‘router’ in the KNX world).

I’ll also give you a tip on how to deal with a KNX device that is physically inaccessible, where that ETS5 really wants you to press that ‘programming’ button on, again, to change anything… but when you just can’t do that (because you don’t know where it is, or because you do know, but you can’t ‘get to it’ physically).