The STKNX is the smallest KNX transceiver today thanks to its VQFNPN24 package of only 4 mm x 4 mm, making it smaller than a grain of rice. We are also the first company to offer a complete KNX Twisted Pair (TP) node, the EVALKITSTKNX, with both our transceiver and a microcontroller on the same board to facilitate developments. Our device passed the KNX-TP1-256 certification, meaning it will work worldwide and it can link up to 255 devices while managing a topology with a maximum length of up to 4,000 meters. Primarily aimed at building automation, the STKNX is part of our efforts to shape the Smart Industry movement by offering a comprehensive solution to popularize KNX solutions so homeowners and building managers can save costs and energy.
KNX, which is an abbreviation for Konnex, is one of the most comprehensive protocols for building automation. One of its strengths is the fact that it is an international open standard officially approved in Europe, China, and the United States. As a result, manufacturers don’t have to fear additional royalties, and they have access to an important market to justify investments. KNX is also versatile since it supports a multitude of way to transport its signal, such as Twisted Pair, power line, wireless, infrared, and Ethernet. TP remains today the most common interface, which is why we decided that build the STKNX transceiver around it. Very simply, the signal travels in parallel to the electrical power supply that feeds all KNX products in the building, while a common kernel ensures that all KNX devices, regardless of their physical layer, can talk to one another.
A Power Efficient KNX Transceiver for a Powerful KNX Network
The history behind the STKNX is fascinating. Initially, ST worked on a KNX ASIC (Application-Specific Integrated Circuit) for select customers. However, the component was so successful that we decided to make a public part number out of it and came with the EVALKITSTKNX development board to help teams surf the new wave of smart building and smarty industry appliances. One of the benefits of the STKNX is that it doesn’t require a crystal oscillator. As a result, the system doesn’t need to synchronize a clock, which simplifies designs and keeps the Bill of Materials down. Moreover, the STKNX can easily interface with our microcontrollers (MCU) by just using a few GPIO pins instead of the more complex UART or I2C protocols. The system is thus more straightforward to program and more modular, simplifying any future changes to the PCB.
Another significant feature of the STKNX is the presence of two voltage regulators on the die. The first one is a 3.3 V / 5 V and 20 mA linear regulator that will help power an external MCU. The second one is a 1 V to 12 V and 250 mA DC/DC step-down switching converter that can efficiently power analog devices, such as sensors. And to make things even better, engineers can use the integrated DC-DC converter to feed the linear regulator, thus reducing losses and optimizing power management while using the smallest KNX module in the industry. Furthermore, the transceiver can also adjust the KNX bus current slew rate to adapt to particular applications to further optimize power consumption.
The Tools That Will Make You Want to Build a KNX Network
The STKNX is also a unique device in our portfolio because we decided to partner with the German company Tapko who built the software stack for our component. Given their extensive knowledge and experience in the KNX standard, our collaboration ensured that we could offer a robust solution that would also help customers receive the appropriate certifications for their products faster. As such, Tapko takes care of the kernel, the application layer, and the protocol’s security features. Developers who acquire the EVALKITSTKNX development board will get to enjoy the Tapko software out of the box since we load it at the factory. The license installed allows for 16 devices, which is more than enough for prototyping purposes, and the software maker has a system in place to get a license that will unlock the possibility of using the 255 devices that the STKNX can manage.
The EVALKITSTKNX development board itself comes with the transceiver, four user-LED and buttons, as well as an STM32F103 MCU to show that it doesn’t take a high-power system to create a KNX device. The Cortex-M3 of our MCU will be more than enough to manage all the requests and operations that will pass through the transceiver. The board also comes with a UNO and Morpho connector to allow the installation of expansion cards to more easily prototype applications. Additionally, we offer an application example that consists of dimming LED lights. With an EVALKITSTKNX and an X-NUCLEO-LED16A1, engineers can start experiencing their first KNX automated systems. The example code is also a great stepping stone for developers that tend use it as a foundation and build on it.
