LabVIEW
saving and plotting acquired data
A very good start, actually. Well done. Give yourself £10. 
You actually can run the code without hardware. DAQmx allows you to create simulated devices and you can use Measurement & Automation Explorer to do so. I don't recall you mentioning what kind of device you have, but if it's not in the list of devices that can be simulated you can always find one that's close, especially since all you're doing is performing a simple voltage read. Then in your code you need to select the channels for whatever device you created. That's how I ran your code.
Code comments:
- My comment about checking whether or not data acquisition was started was based on the UI state checking if a user pressed any of the front panel buttons. Since you've changed the state machine operation such that the "Collect" state goes back to itself unless the Stop or Exit has been pressed (an acceptable alternative), this is no longer necessary. However, you still need to check if the user pressed on the Exit button in the UI state. Otherwise, there's no way to stop the program if you're in the UI state.
- "Also as the program is at the moment would it be better to move the creation of the TDMS file into the start state?" Yes, for the reasons you stated. The Initialize state should take care of setting up the front panel, and initializing any internal variables that a program requires. You should not perform any I/O operation (such as creating file that are dependent on a data acquisition) until a user specifically starts an acquisition.
- "I created the state machine using the labview
template and i'm unsure what effect the 'milliseconds to wait' function
will have. Does this add a wait in between each iteration in the loop,
therefore meaning that in every loop there will be a 100 millisecond or
so gap in my recorded data? " Yes, it will. You can mitigate this by moving the wait inside the UI case, since that's the only place where it matters. In your "Stop" state if the user is simply stopping, go back to the UI state.
- You are converting a Boolean into a floating point value, only to checkif the value is zero in the "Stop" state. Instead, have the shift register pass around a Boolean directly (in this case the value of the Exit button).
- You should have some form of error checking so that if an error occurs in any state you will know it. As you have it now, the only way you will get an error dialog is when the user presses the Stop button. If, say, an error occurs when you configure the DAQ and the user presses Exit rather than Stop, you will never know about the error. One way to handle this is to have an "Error" state that the state machine goes to whenever an error gets generated. What you do in this "Error" state is really up to you. You can have something as simple as displaying a dialog and then pass out a no error condition so the state machine can continue (e.g., to try to restart the acquisition). Or, you can have it display the dialog and then immediately terminate the program.
- Do not leave the shift registers uninitialized. If you run the VI again, the shift registers will "remember" the value from last time. Note that this can be taken care of in the "Initialize" state.
- Don't know if this is going to be an issue or not, but your filename is based on hour/minute. Thus, if you stop an acquisition that has been running for less than a minute and then start it again while still within that same minute, then you will get an error when trying to create the TDMS file. Like I said, not sure if this is an issue for you.
Ha ha, touché! I'd better get on ebay!
Couple of things i'm having trouble with:
- can i have my buttons appearing in more than one case? So for example my exit button currently appears in the collect case, can i also have it in the UI case somehow so that I can allow the program to be stopped at that point? Or do i have to do this some other way?
- when trying to move the creation of the TDMS file to the start state, presumably i have to also move the 'set file properties (TDMS).vi' with it?
- Regarding initialising the shift registers, is this just a case of setting a zero value for them, as with the (what was a floating point but is not a boolean shift register)? You say that at the stop state if the user is only stopping then to go back to the UI state, do the shift registers not need reinitialising at this point before the next set of data can be recorded?
- I like the idea of having an error state and i've found a function to reset the error once a dialog box has been shown, but i'm not sure how to navigate the program to the error state when an error occurs. At present anytime i need to choose between possible states it's done by just using the select function to choose between 2 options. How can i add in the 3rd option of moving to the error state, and make this take precedence over the other 2 options?
When it comes to actually using the system for real the hour and minute time stamp should be fine, but for testing the program i might add in seconds too just to prevent anything going wrong.
I'm really pleased with how well it's gone so far, thanks for your patience!
