Konnekting Rail System XL

Description

The Konnekting Rail System XL (KRS-XL) is a bunch of modular hard- and software for building devices in big DIN Rail Cases. It is designed for applications with a high number of channels.

Design ideas and principles

The itention for developing this system was to reduce the costs of the devices. Because Bus connection, case, microcontroller are often the most expensive parts, a high number of channels very effectively reduces the cost per channel. So the system is designed for use in 6, 9 and 12 TE DIN-Rail cases.

Another important design priciple was the use of prebuild componentes. Not only to reduce developement complexity and enable persons with limited soldering skills and tools to build it, but also to make it easier to repair devices in the future. On the Controller Board three prebuild components which are generally availible are used: a pluggable microcontroller board, a pluggable Bus interface and a display module.

Modularity was added later in the developement phase, but was a logical step. The Controller Board is designed to be used in all devices within this system. It contains not only the microcontroller and bus interface, but also the user interface (frontend). To make it possible to handle high channel numbers and also to have one common hardware, a 320x240 px 2.2" Display is used as UI, operated by 4 buttons. To improve supply quality, it is not only possible to use the µBCU, but also the Siemens BCU. Unfortunately, the Siemens BCU comes with some limitations regarding power consumption. To fit the needs for every device regarding power supply and galvanic insulation there is a wide range of assembly variants and solder jumper options.

Because of the need to have the Controller Board at the top (because of the UI) and the fact that the pluggable component need some space, I choose a two PCB design - the big application PCB at the bottom and a the Controller Board at the top. With the ApraRail DB DIN Rail casing series, KRS-XL comes with quite robust, widely availible (Reichelt, Amazon) casings. Unfortunately in this casings there is no possibilty to connect to the top PCB - so KNX and if neccessary DC power have to be connected to the application PCB which is connected to the Controller Board.

To enable easy replacement, repair or improvement, two-part conectors are used. They can be unplugged from the device an remain in the cabinet without the danger of short circuits, and the cany easily plugged in again. To achieve this, Phoenix combicon MSTB with 5.08 pitch (to enable bread board use at application PCB) are used. They are avaiblibe up to 16 amps and can also be used with 230V.

Because there is no possibility to have a standard KNX connector with the ApraRAIL DB casings, the Combicon connector is also used of standard for the KNX connection. Plugs with two wire per pin are availibe, so the devices can be chained.

Controller Board CB6-9-12

Microcontroller Board

A Adafruit ItsyBitsy M0 Express Board was the almost perfect solution for the needs of KRS-XL:

• ATSAMD21 controller ("standard" controller for Konnekting) with sufficient cpu power, RAM, and FLASH
• SPI Flash to enable FOTB
• good availablity
• quality supllier
• pin compatible big brother ItsyBitsy M4 with Cortex M4 CPU available