Initial rats nest on arduino works with 4 buttons and a bluetooth adapter. Annoying tidbit you need to have the usb unplugged if you want to use the bluetooth or vice versa.  Makes reprogramming slightly more annoying. Oh well.  Right now the systems waits for a ready "1" from bluetooth module. Then it waits for the first input to turn high. After that it waits for input 2,3,4 etc until all have been triggered and returns the difference in time between input 2,3,4 and the first input. In my case it will tell me my 15m, 30m and 45m sprint times times. Eventually someone might desire to make it more flexible where you can pass in the number of timers.  We will see when the app is made if I get to it or not....

Code is on GitHub