LabVIEW
Using one button to start and stop
Generally, you should have a single loop to handle your GUI. That is the loop which contains your Event Structure. You can use Notifiers or Queues to send messages to your other loops to start acquisition, stop acquisition, close, etc. Look into the Queued Message Handler for more details.
You need to start over and implement a simple state machine with one single event structure. Your "Acquire" event structure is outside and can only execute once. This means that if somebody would press that button again later, your UI will lock up forever, because the event can no longer be serviced.
As a first step, get rid of all the hardware interactions and create an UI that simulates the hardware. Once that works as desired, add the IO.
As I've not yet installed LabVIEW 2019 I cannot open your code. However, typically this would be done with an event structure for your button. You then send the appropriate message based on the state of the button.
I use Channel Wires all the time. However, you are using the wrong Channel Wire. The Stream Channel Wire is, indeed, a "super Queue", suitable for point-to-point wiring. But what you need is a Channel Wire that accepts Branching, like a Tag or a Messenger.
Here's a picture of a Event-driven State Machine, with Tag Channels carrying State information from the middle (State Machine) loop to itself, and also from the top (Event) Loop to the State Machine. In addition, there is a Producer/Consumer design between the Sampling Loop in the State Machine and the Display Loop below it. I created this is 2016, when Channel Wires were first available, so you should be able to open it with whatever version of LabVIEW you are using. Note that the Tag Channel allows the information to branch and merge, acting as a Feed-back loop and as an "Event-injection" pathway.
A related Design Pattern to the Event-driven State Machine is the Queued Message Handler (there's a QMH Project Template that ships with LabVIEW). I frequently create a "Channel Message Handler" by replacing the Message Queue with a Messenger Channel. There's a "natural mapping" between the QMH and the CMH -- both use a "Message Cluster" consisting of an Enum representing "What to do" and a Variant representing optional Data. I generally create a "Send Message" VI that takes the Enum and an optional Argument and creates a Messenger Channel output, and a "Receive Message" VI (there's only one, at the input side of the Message Loop) that takes the Messenger and outputs the Enum and optional (Variant) Argument.
I've also attached this VI as a LabVIEW 2016 file.
As to creating a "One-Button Front Panel" (which was the reason for your Post) -- think about your User, who doesn't want to "guess" what button to push, nor guess what the "one button" does. Have Your Cake and Eat It, Too -- create three buttons, with obvious names like "Play", "Pause", and "Stop". If you want the User to push only one, then set the Visible property of the other Buttons to False. Once you are done with a Button (such as after you push "Play"), in the "Play" State, set the "Play" Visible Property to False, and set the "Stop" and/or "Pause" Visibility to True. Note you can also place the buttons "on top of" each other -- LabVIEW has convenienntly made it so you can't press an invisible Button.
Bob Schor
