Trigger case structure using OPC variable

[jdruano]

Hi,

I am using OPC to communicate Labview with a Siemens PLC. One memory location from the PLC will work as a flag that triggers a case structure in Labview.

However I only want to trigger that case structure once.

So far the vi seems to work but the case structure just keeps on executing because I do not know a way to use the flag of the PLC as a edge trigger.

Could anyone help me please?

[Gregory]

OpenG toolkit actually has a Boolean Trigger which may be useful. Here is a simple implementation with shift registers. I'll let you fine tune it if you only want it on the rising edge 🙂

[Jacobson-ni]

If you are feeling stuck I would search more specifically for LabVIEW FPGA rising edge detection. It is something that is done pretty often in FPGA and there are some really clever implementations. A lot of the examples will use feedback nodes which will make it really easy to put in a subVI as well.

[jdruano]

Thanks a lot man! I didn't know about openg libraries, the boolean trigger over there saved me.