RC cars: IR 2.4GHZ multi client Lap timer for Arduino

sadly I cannot find a specific topic posting finished projects, so @admins feel free to move this topic.

I’m a RC-car driver and often use temporary race tracks for bashing with my friend. So this project was born:
IR 2.4GHZ multi client Lap timer for Arduino
Highly transportable IR-tracking lap timer for up to 6 different RC-cars.

Function description:
You need at least 3 devices:

  • IR-generator pillar: This device contains an Arduino mini generating a very short IR code. Via 3 IR-LED’s the code is beamed permanently
  • Transponder box within car: Arduino Nano/mini + IR receiver + NRF24L01 module. If a IR signal code is recognised (car is passing the IR pillar) a short unique code will be send via the NRF2401 module to the master box. Up to 6 different transponder can be used (Currently only 2 are implemented)
  • Master Box: Arduino Nano + NRF24L01 module + Encoder + Display. Collecting the transponder data for generating lap times,…

The whole project (code, details, photos) can be downloaded here:

Whole project is on instructables:

Thanks for sharing.

"pillow" sounds like it may be the wrong word. A pillow is the soft thing I rest my head on when I am sleeping.

Is the IR transmission restricted to a narrow beam to ensure timing accuracy?

What is the greatest distance at which a car can receive the IR pulses?


Thanks Robin, I changed every "pillow" with "pillar".
I didn't tested the whole range of the IR signal under all conditions (like full sun), but with my 3 IR LED's (consumption 60mAh) the range is over 10 meter plus. Enough for the width of a race track.
If the transponder is within the IR range it fires up and 2.4GHZ signal to the master box. To get best results it might be an idea to cover one side of the IR-Led's, because the angle of my ones are 20 degrees:

-LED--> ^
####### ^
-cover-- ^

What is the accuracy of your time measurement - plus or minus how many millisecs?

Perhaps if the cars always approach the IR beam from the same direction the width of the beam is not material - it is their first encounter that triggers the timing?

Can your system deal with 2 (or more) cars side by side?

I have seen previous Threads about lap timing systems without a solution.


The accuracy of time measurements depends on how accurate you get the beam. So if you cover (red line) the IR LED and the IR receiver like on the picture you'll get best results:

The NRF24L01 communication is very fast, if the first message is recognized it's about 1ms, the second (if the first fails) follows in 2ms, third in 4ms and so on.
The IR signal is also very fast, much less than every "standard" IR signal (remote controller use about 16-32bit!) because of it's slim code.

Two cars parallel. This also depends on the construction, see the picture for optimal results:

So the real trick is to use more than one IR LED'S in a row within a special angle.

Are all the LEDs transmitting the same signal? Or is there a different signal for each car?

What are the best results you have achieved?

I am familiar with the nRF24 - I am using them for controlling model trains.

Just out of curiosity what size are the cars you are using?
And what size is your pillar?


It's the same signal, different signals wouldn't make any sense. You can look into the code on my drive account.
I use a 1:10 buggy (TeamC TC02 evo) and my friend a traxxas slash (also 1:10 but with 1:8 tire, this car looks more like a 1:8 model), so unequal "partners", they won't hide the IR signal by "nature". I cannot say what are the "best results", because I would also need a laser line within the pillar for exact matching (cross checking) when the car is passing the line and compare the results with the incoming signal (Maybe I'll try this out in the future). It also depends on which place you fix the IR-receiver on the car avoiding any different angle than 90 degrees (lower angle: you get the signal too soon, higher angle: you get the signal too late). All I can say is that it works quiet good without any missing triggers. There is also one thing:
If a signal is delivered with delay, this won't be a problem only in the final lap in case of a "photo finish".
If the car pass (lets say in lap 7/10) the line and there is a short delay sending the signal you'll have this missing milliseconds as "bonus" for the next lap, because physically the car is this missing milliseconds beyond the IR-line and this will be subtracted the next lap. So maybe bad because you'll cheat the "fastest lap" a little bit .
The height of the pillar is about 40 centimeters.
I know the system is far away from "perfect", but as a cheap "just for fun" solution more than comfortable. Keep in mind that professional time tracking systems costs beyond 200 Euros.
A far better solution would be a RFID system. But I'm not familiar with it: So I have no plan which transmission strength/length is needed, but I guess far more than the cheap RFID modules you can get on Ebay or Aliexpress.

I have been commenting on this because it seems like it may be very practical.

Again, thanks for sharing.


Have you tested your lap timer with sunlight ??

I have developed 5 diferent version of lap timers, and sunlight, kills all my prototipes. Indoor works perfect with ranges over 5 meters, but outdoor... max 30cm. A very poor result.

sorry for my english, i'm from spain.