Initial situation

RS485 repeaters are readily available on the market. So why redevelop the famous wheel again? The customer, active in the field of visualization systems for buses, streetcars and trains, wants to retrofit the compositions of a regional train with modern digital information systems. High demands are made on the dielectric strength and interference immunity of the data transmission. The communication lines provided for this purpose are already occupied with other functions, which must continue to function.


Meng Engineering was commissioned to create a concept for an intelligent RS485 repeater based on meetings, discussion documents, and on-site measurements, which would take into account the special requirements, such as multiple occupancy of the communication lines, and high external voltage exposure. Some points remained open. The field test had to provide clarity here.

The repeater is based on two galvanically isolated half-duplex transmit and receive circuits, which are connected to the ARM7 microcontroller LPC210x via optocouplers. The application on the 32bit controller acts as an intelligent bidirectional FIFO. The directional interlocking is done based on the received data from the respective input. The data appears shortly after on the opposite RS485 output. The controller is currently not used to capacity. This offers much room for extensions in the area of line diagnostics, logging, framing of the data, dynamic measuring of the line parameters, etc.

The software is based on a small portable RTOS, which is available in C source code, and makes adjustments easy. This was necessary in the driver area of the serial interfaces. The RTOS is HW independent. It is distributed, maintained and further developed by the company The customer could be offered a solution, which uses the existing cable and connection infrastructure optimally. An expensive installation effort can thus be avoided.

Meng Engineering took over all work for the realization of this assembly. These are concept work, design, schematic, layout, SW adaptation, as well as the coordination in the area of material procurement logistics and fabrication / testing.

Do you have a similar situation? We would be pleased to learn about your requirements and boundary conditions.