write data to a logbook file only when a boolean indicator changes

[Tom_Pa]

Hello

I need to write my local variable state to a simple txt file only when it's true or false state changes.
for example, when my local variable 'temperature too high' is true, I need something like: temperature too high.
When it changes back to false i need: temperature OK. This with a date stamp.
It already worked to get a date stamp and to write the true or false state down but it always gets stuck in a while loop so the program keeps writing the same sentence.

[NIquist]

Post your code so we can do more than guess at what the problem might be.  

[Tom_Pa]

I had to take a picture with my phone because we're not allowed to connect the computers with an usb drive, I hope you can see it clear.
I know this while loop causes the program to write the same sentence over and over again but I don't know an other way to do it right.
Thanks 

[GerdW · Accepted solution]

Hi Tom,

pseudocode:

IF current boolean state <> previous boolean state THEN
   save data to file
ENDIF

To check boolean state changes you can use the BooleanCrossing-PtByPt function…

[_Bryan]

That makes life a little easier.   I did not know that was there.  I guess I need to get out and look around more.

[Tom_Pa]

GerdW thank you very much, it works perfect now!