String Limitations

When programming in step7, strings variables can be a little tricky and cumbersome. This is because the software absolute addressing protocol makes it hard to manage the variable memory space required for strings and string manipulation. This problem became clearer during the HMI programming stage.  Especially when trying to write the order receipt on screen7. We had the expectation that we could just create a string variable arrays and called them later to print them/display them similarly to other software packages such as C, C++, MATLAB and JAVA but found it to be impossible.

After referring to online tutorials and the Siemens manuals, we found the best method to accomplish our task is to use individual text boxes on different layers and control its appearance using the WinCC animation tools. Using this method we accomplished our task but took a very long time and was cumbersome. Having learnt this limitation of the Step7 and WinCC software, we look forward to learn about SCADA software next semester.


Improved group collaboration and efficiency using Graph and HMI

Our approach for having the HMI functions and sequence follow the State Machine design sequences, allowed our group to work simultaneously increasing both productivity and communication. At any-one-time, one member worked on the PLC coding and functions while the remaining members worked on the screen layout/animation and the I/O triggering the state transitions.