This CoDeSys 3.5 project is built for home automation purposes. The goal of the approach is to perform any critical operations like reading inputs, switching light, controlling sunscreens, etc. Inside the PLC itself and make use of MQTT events to send events to an MQTT broker. Using MQTT subscriptions it's possible to send commands to the PLC to control -for example- outputs.
The purpose? Redundancy on a software level but also on a hardware level!
The project is developed using the IEC 61131-3 standard, there are multiple development environments with their own runtime that support the standard:
Core processing logic is executed in the (robust) PLC. Meaning that events like reading pushbuttons/switches, updating outputs are executed in the PLC software. To enable integration with external software the PLC sends out events to an MQTT broker when events occur (like pushbutton events, outputs that change state). MQTT subscriptions are enabled as well to allow control from the external software to control -for example- outputs.
More information on the software architecture here.
Basic function blocks for basic IO events and operations.
Function blocks developed to easily set and get values from the processing logic through MQTT.
With many PLCs having a onboard RS485 serial port it is a popular protocol to create a robust Modbus RTU sensor network.
How to use Modbus RTU differs depending on the PLC/development environment used. The topics belows address the usage of Modbus RTU in several development environments:
To translate the byte array received by the modbus device to their actual value and send their values through MQTT the function blocks below have been developed. Note that a specific function block is required for each type of Modbus RTU device.
In addition to the above a buscontroller function block (FB_RS485_BUSCONTROLLER) is used to control access to the RS485 bus between multiple RS485 device function blocks.
The following libraries are used in this PLC project and can be found under
Special thanks to StefanDreyer for his assistance in some of the MQTT aspects of this project and his great work on his open-source CoDeSys MQTT library.