Simpler control panel design for home and building automation with KNX

In recent years, the adoption of smart technologies in enterprises has increased, creating a more automated world. One of the ways to automate is through actors networked to a central controller. This includes smart actuators that make decisions based on data. The data used can be aggregated by cloud services or collected locally using other networked actors such as smart sensors.

By: Mike Sandyck, ON semiconductor

In recent years, the adoption of smart technologies in enterprises has increased, creating a more automated world. One of the ways to automate is through actors networked to a central controller. This includes smart actuators that make decisions based on data. The data used can be aggregated by cloud services or collected locally using other networked actors such as smart sensors.

This level of automation helps improve energy efficiency and gives businesses and homeowners more control over their surroundings. This enables functions such as monitoring, remote management, hydrometering, and enhanced security.

There are many types of networks that enable this level of building management and automation, but one network stands out for its rapid growth in industrialized countries around the world. KNX® is the only open and vendor-independent standard in the world, with nearly 400 million connected devices deployed worldwide, and is regarded as the leading protocol for this application.

In the KNX Association, there are more than 500 member companies and more than 93,000 installation partners. Together, they have developed over 8,000 certified products, deployed in at least 190 different countries. The KNX network is very flexible, versatile and scalable, supporting 256 addressable devices on a 1000 m network segment and up to 256 network segments in one network. The communication protocol of the KNX bus is standardized by several international and regional standards (Table 1), managed by the KNX Association. It brings together the advantages of some traditional buses to create an OSI-based protocol that can be deployed over a variety of mediums such as twisted pair, RF, and IP.

Table 1. KNX bus international and regional communication standards

Probably the most popular of these mediums is simple twisted pair. In this configuration, the cable transmits both data and power, but the power provided is purely the circuit that feeds the node; any power required by the actuator needs to be provided separately. In this respect, it is similar to copper telephone wire.

Interoperability in Smart Buildings

This analogy extends to describing how devices from different vendors are compatible in a KNX network. Interoperability is a key requirement for any infrastructure, enabling multiple suppliers and manufacturers. In this case, interoperability is guaranteed through a certification program, managed by the KNX Association. Part of the certification requires manufacturers to demonstrate compliance with key parts of the KNX specification, including protocol characteristics and supported profiles. The product must also meet the networking requirements of standard data types and optional function modules.

KNX is connecting the world of automation

This level of compliance is a challenge for OEMs, which is not the purpose of the KNX Association. It is in their interests and the interests of the wider ecosystem to bring new products to market as simply and practicably as possible. To support this, the Association offers a simpler certification path for new products based on previously certified products.

The official term is derivative product, or OEM product, for certified products from KNX Association members. OEMs are then free to sell their product and label it themselves without any further testing.

This inherited compliance involves the two most critical elements of the system, the physical layer and the software stack. If these elements are certified and not modified, the OEM product is considered compliant and can be sold as such.

Make KNX simpler

To accelerate the adoption of building automation applications, onsemi has developed the industry’s first KNX pre-certified system-in-package (SiP). The NCN5140S contains all the key and certifiable elements of a KNX device, including the physical layer (PHY) and media access controller (MAC), as well as the software stack. These elements are integrated into the NCN5140S along with an Arm® Cortex®-M0+-based microcontroller (Figure 2).

Since the PHY and protocol stack are pre-certified, NCN5140S based products are considered derivative or OEM products. Therefore, new products only need to be accompanied by a KNX Product Modification Statement and do not require full compliance testing. This significantly saves OEMs time and cost in developing new KNX products.

SiP is designed for the development of networked controllers, usually in the form of user panels, for controlling lights, heating, ventilation and air conditioning (HVAC) systems, curtains and blinds, and access control systems.

The NCN5140S can be further customized with a software tool that allows installers to configure the panel at installation time. This is done with Engineering Tool Software or ETS, a manufacturer-independent configuration tool provided by the KNX Association. ETS is used to access certified product details in the database and to configure certified products.

Since this advanced customization does not change the underlying firmware, certification is not affected and the SiP can be used as the basis for a variety of products. This is not the case for control panels developed from components of the system. It is this pre-integration and certification that allows NCN5140S-based products to be evaluated as derivatives.

Simplified capacitive touch sensing

Developing touch-sensitive interfaces can be difficult. They tend to work by detecting small changes in capacitance, on the order of picofarads. Care is still required when designing the PCB, ON Semiconductor also provides the firmware required to interface with the capacitive touch-sensing buttons. This application software is provided as a binary file along with the certified stack. This file needs to be programmed into the NCN5140S during assembly, but once installed it can be configured during installation using ETS.

During assembly and installation, OEMs must effectively work through three stages:

1. Flash the binary to the NCN5140S microcontroller
2. Configure the product’s unique net ID and application options through the KNX bus interface
3. Use KNX ETS database to set device parameters

For example, during production, the NCN5140S can be programmed and then configured with a unique network ID. At this point, the number and type of inputs will be defined (up to 8 general-purpose or capacitive touch-sensitive buttons), as is the operating mode (eg on/off or dimming). The type and number of outputs (simple or RGB LED) will also be set.

The installer will configure the controller functions through the ETS database. For example, this would include device name, switching behavior, dimming parameters, timers (if applicable), and scenarios (such as dimming levels at different times, different rooms, or different daylight conditions).


The KNX protocol is a powerful platform that supports home and building automation. There is a growing need for this level of automation, which, for example, can be combined with smart meters to help make all types of buildings more energy efficient.

As this ecosystem continues to grow, with thousands of installers around the world, KNX is becoming the dominant protocol in building automation. The NCN5140S is an important step in simplifying the development and certification of KNX products.

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