The start line is rather simple: its only job is to allow racers to input their ID number and send the start signal to the finish line when the start wand is tripped

This is accomplished with a minimal bill of materials. Besides general electrical prototyping resources and 3d printed parts (which can be found in the next section), here is what you will need:

1. Arduino Uno
   1. Xbee Arduino Shield
2. 2.4 Ghz Xbee with compatible RPSMA Antenna
3. 9 Button Keypad
4. Micro Switch (triggerable with 0.005N-m of torque)
5. Extensible Spring (Approximately 1/4” x 7/8”)

This Xbee works over 4000 feet with line of sight. If you need less distance, others can be substituted to save on cost. Just make sure you find a compatible antenna!

A Note Regarding Power Supplies: We have refrained from listing a power supply in the bill of materials, as we have found different solutions work well for different scenarios. Beyond simply wiring up a 9 volt battery or multiple AA batteries in parallel, we have also had success using USB battery banks that are widely available for charging cell phones. You simple need to take a USB cable and cut it open to expose the positive and ground wires, then plug these into the power terminals of the Arduino.