Basic control with a serial port

[DarkMarc86]

Hi everyone,

I would like to do some basic control with Labview. I have four digital 10V inputs and I would like to send four outputs. I will write a basic Labview program that performs a sequence of outputs seperated with timing delays ranging from 5ms to about 10s. The most important requirements in this tast are reliability, repeatability and accuracy of the timing intervals. Can this be done with Labview reading and writing to a simple serial port? I'm guessing there would be issues with the timing intervals not being exactly as you set them to be?

[Dennis_Knutson]

There are problems with timing on any non-deterministic operating system. It has nothing to do with LabVIEW or serial communication. If you need precise timing, you should look at LabVIEW real-time.

[crossrulz]

Or if you want to get into some real fun, LabVIEW FPGA.

As Dennis said, Windows in not a deterministic operating system.  This means that the code is not guaranteed to work with reliable timing.  Mostly because you have to allow other processes to work.  Going to RT, you have a deterministic operating system.  You will still have some jitter, but nearly as much as with Windows.  Going to FPGA, you are actually programming hardware.  Hardware will give you the least amount of jitter.

[DarkMarc86]

So lets say I want to be able to repeatedly output signals with accurate 5ms delays (with a tolerance of say 1ms), will I be able to use regular Labview with a cDAQ chassis and DI/O card, or do I need to go to Labview real time? I would like to be able to modify the program on the fly (particularly the length of the timing delays) and have a GUI as well. 

[Dennis_Knutson]

If you get a DAQ device that supports hardware timed output, then timing will be very accurate.