GPS Speed plugin or show any line from text file and change

Hello!

I try to use TLB as control panel for carPC.
I set all what I want, but there is one problem, I can't solve.
I need to see car speed from GPS every time.
I get this data from COMxx and want to see it as TLB Clock.

So, possible to make simply. I put the speed value in the txt file and plugin get this value any XXXms and shows (with font and color choise).

So - If you explane how to write plugin I can make it by myself :-)

Best regards, Vitaly