How to implement boolean comparison and event structure?

Hello all,
I'm currently developing an undergraduate lab in which a laptop sends out a voltage via USB-6008 to a circuit board with an op-amp, the voltage is amplified, and then sent back into the laptop. The student is going to have to determine an "unknown" voltage which will run in the background (they can do this by a step test, graph V_in vs V_out and extrapolate to the x-axis).
Currently, I have two loops that are independent in my VI. The first loop is used to "Set the zero." When 0 voltage (V_in) is sent out of the laptop it returns a value around -1.40V (V_out) typically. Thus, I created the first loop to average this value. The second loop, averages the V_out values that come into the laptop as the V_in numeric control changes. Then I take the "set zero" value from the first loop and subtract it from the second loop average to get as close to 0V for V_out when V_in is 0V.
The problem I'm facing is, the event structure waits for the V_in numeric control value change, but after "SET ZERO" is pressed, if there is an unknown value, it will not be added to the average for V_out until V_in is changed by the user. So, I tried implementing a comparison algorithm in the "[0] Timeout Case." This algorithm works for step tests with positive values for V_in, but there are two problems.
1) Negative values cannot be used for V_in
2) If a user uses increasing positive values for V_in there is no trouble, but if they try to go back to 0, the value change event has been called and it is added to V_out as well as the timeout case.
Sorry for the extremely long post, but I've been banging my head over this and can't figure out how to properly implement this. I'm using LabVIEW 8.0.
Attachments:
Average Reset Test.vi ‏371 KB

OK you have bigger problems than Raven's Fan is pointing out.
When the first event loop stops ( after pressing "") (the boolean text is "Set Zero") The second loop may start- (AND PROCESSES all of the events it was registered to process before the loop started!) that would enclude the value change event from "" (The boolean text is Stop) Being pressed bebore the loop started. Of course, since the labels of "Set Zero" and Stop are identical nulls....................................................BOTH event trigger at the same time and are processed as soon as the event loop they are registerd to is available.
Get it ... The two buttons labeled "" both queue Value change events to both loops registered to act on the value change of the control labled ""!
Both loops will do what you programmed in the case of "" Value Change! This can, (as you have observered) lead to confusing code actions.
Do avoid controls with duplicate labels (There is a VI Analizer test for that!) Do avoid multiple event structures in the same hierarchy.
DO NOT bring this to your studients to help you learn LabVIEW! We get enough studii asking embarassing questions
VI Analizer will help you provide sound templates. If you need help with that hit my sig line- e-mail me and I'll always be willing to help.
Jeff

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"Lee Robertson" <[email protected]> wrote in message
news:[email protected]...
>I am just learning to use event structures to improve operation of front
>panels.  At the moment, I am working on a tab strucrture we use to
>montinor/set program paramters.  VArious parametera are displayed on
>each tab as controls (not indicators) and are constanly updated sice they
>can be modified elsewhere by other pieces of code.  We controls are
>normally disabled via a property node so they behave more like indicators
>and the values are updated by writing to a local variable (I know this is
>evil but it works in this case).  There is a boolean on each tab that
>toggles between "monitoring" and "changing" modes (or states).  When
>toggles to "changing" (or setting) parameters the monitoring activities are
>suspended and the control are enabbled.  After making the desired
>changes the controls are either read and the changes implimented or get
>rest based on some other boolean controls, the parameters controls are then
>disables and monitoring resumes.  The issue is that many users fing
>the need to toggle between "monitorsing" and "changing" modes to be
>confusing.  I want to replace this switch with an event.  If the
>user clicks on any of the parameters controls in a tab, I want to go into
>changing mode rather than using the "monitoring"/"changing" boolean
>control.  All other asspects are handled as before.  My problem
>is than if I use a mousedown event to go into "changing" mode and the user
>clicks on several parameters to shift the keyboard focus to edit more than
>one parameter, these subsequent mose clciks get processed as new events
>when change mode is exited.  This means that as soon as it returns to
>"monitoring" mode it jumps immeadiately back to "changing" mode.  How
>should I structure the events to avoid this problem?
>  
> Thanks,
>  
> --Lee

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