Triggering Updates to Components

Ok, so I got my hands on a Kinect and want to play in Grasshopper. I have no problems getting it to function using Quokka. I am attempting to create an archery simulator, totally useless, but I have some free time.

The idea is that the line between the two points which represent hands is the arrow, vector, and magnitude of the arrow. Since Kinect cannot read finger gestures, I would like the arrow to "fire" once a certain distance between the hands has been reached.

Using Hoopsnake, I'd like to have the arrow fire one x is > length. So, if x > length then True, else False. Yet, because the distance between hands is constantly changing, the value "True" is constantly being re-sent to Hoopsnake, causing it to fire constantly. At least, this is my deduction.

Is there a way to only send the True value when it changes from False? Am I mis-interpreting the function of the trigger on Hoopsnake? Can I write a custom component which will achieve the same function?

Thanks!

Shane