You can use the timer by powering the Feather through USB or using a Lithium Ion battery.
Once the car goes past both sensors the speed will be displayed. I did not have another track piece to connect to the left side. But both sides are compatible with Hot Wheels tracks.
I designed the timer to fit taller vehicles but some are too wide for the track and will not fit. This vehicle was an example, it was just a bit too wide.