40-YD Dash Timer w/splits

I'm building a timer used to record 40 yd dash times with 10 and 20 yd spit times. I'm still in the initial setup of this project but wanted to see what the best course of action would be. I plan on using IR emitter/receiver.

Option 1: Use 4 "gates" located at START, 10 YDS, 20 YDS, and 40 YDS. For the IR emitters gates on one side, use standalone circuits that are battery powered and modulate at 38KHz. On the other side use 4 Arduino Unos to hookup a IR receiver on each Uno to sense a break in IR beam. The START Uno will be the Master and the other 3 are Slaves. The START Uno will also have a display that shows the times of the 10, 20 splits as well as the overall 40 time. A manual power/reset button is placed on the START Uno to control the other boards as well.

Option 2: Use 4 "gates" located at START, 10 YDS, 20 YDS, and 40 YDS. Use IR emitter/sensor combo on one side of the gate powered by 4 arduinos using I2C to create a Master/Slave communication. The other side of the gates will have a reflector to send the IR signal back to the sensor. Sensor senses break in signal once runner passes through. Modulated at 38KHz. Same as Option 1 above with displaying and manual power/reset.

Option 3: Only use 2 Unos at START and FINISH line (40 yards) with the 10 YD and 20 YD gates having IR sensor circuits that feed their signals back to Uno START. Uno FINISH feeds it's signal back to Uno START only with the same setup of either Option 1 or 2. LCD Display and manual power/reset.

I'm leaning towards Option 3 with using the setup of Option 2 since I believe this will save on power and $$$ for this project. Just want everyone's thoughts on what would be best.


It would be easier to synchronize the timing if all the gates are wired to one Arduino.


I agree with Robin, the Arduino at the start and 9.14m and 18.28m points would have almost no work to do. All they would do is detect a break in the beam and send a HIGH output to the master. Hardly worthy of a 16MHz chip. If you want to save money, eliminate them from the design. Perhaps you could use cat5 cable to link the 3 ir modules to the master Arduino.

How big does the display need to be? A small LCD or a large display visible to the spectators?

What resolution do you need, 1/10, 1/100, milliSeconds?
I assume all the gates are hardwired back to the Master.

Tom… :slight_smile:

@Robin2: I think it would be good to go this route. Thanks for your advice!

@PaulRB: The display doesn’t need to be big at all. Just enough to show the times to record it. Spectators don’t need to see it at the moment. Maybe like a 3.5" display at most.

@TomGeorge: I need the time to be accurate to 1/100 of a second and your assumption is correct. I found some code online that should help with emulating a stopwatch but I need to alter the code to detect time at each gate.