Creating a latch with an LED indicator control

[M3GAPL3X]

Hi Guys,

Labview newbie here and am trying to build a Labview simulation of a basic sensor. Here is the question I can't seem to figure out.

Basically I have one input - a on/off switch. When the switch is on, it will simulate a crucial event where the user must pay attention to it. This will light up an LED for this event. When the system is off, the system is running fine and there is an led indicator for that also. For the crucial event, I want the LED to stay on until the user sees it and acknowledges it --> he or she can acknowledge the event until he/she clicks on the LED which will turn it off. This LED will stay on even if the on/off switch is in the off state because I want the user to see that the crucial event actually occured. 

I have this so far (really basic):

I want the bottom LED to stay on until it is acknowleded!

Any insights on this would help! Thanks!

[altenbach · Accepted solution]

You would use a shift register for the historic status, e.g. as follows (LabVIEW 8.5):

Message Edited by altenbach on 11-01-2008 11:21 AM

[M3GAPL3X]

Thanks altenback! I'll definately give this a true and understand the logic behind it! 

[M3GAPL3X]

Hi altenback,

Just wondering, what is the purpose of that timer to wait 100 ms?

[altenbach]

A loop that just services user interactions, does not need to spin millions of times per second, consuming 100% of the CPU. It is sufficient to spin it maybe 10x per second, which drops the CPU usage to 0.001%. A big difference, especially if you have many other things running on the computer.

[M3GAPL3X]

Thanks for the explanation. Can you please give me a brief explanation of the shift register connecting to the output of the select switch? From what I am reading, the switch statement either returns an on or off depending on the reset switch.

Thanks in advance. You have really helped me tons!

[altenbach]

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M3GAPL3X wrote:

From what I am reading, the switch statement either returns an on or off depending on the reset switch.

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It returns either an OFF (If reset is true) or the historic status (The output of the boolean OR operation of the historic fault value and the current fault value. This value is either true or false, depending on the fault history.

Initially, the shift register is FALSE. Once the alarm is tripped, the shift register will contain a TRUE until the reset is pressed, no matter how long you wait.

[lauraalkhoury]

How would one reset the Historical Status, after, say, 5 minutes?

[altenbach]

Measure the elapsed time with each iteration and act accordingly if the boolean is TRUE and the time has elapsed.

Let me know if you have problems with that.

[lauraalkhoury]

To clarify, I only want to programmatically reset the Historical Status (after 5 mins) AFTER it's been switched to false/low.

My problem is getting the Elapsed Time Express VI to start only after Historical Status is switched to false.

Then I would wait 5 mins and set the Historical Status back to true, as you said.