GPS Laptimer

would like the opinion on the feasibility of the gadget, that I mention on the subject field. The general idea is to use an arduino, with a GPS, Xbee, infrared receiver and lcd (nokia,etc) shields. The trigger for start counting each lap would be one of the coordinates, (because, with the width of the track, the other one would vary) and the beam of infrared to confirm (or, if possible, a coded signal for preventing being triggered by another infrared beam). It would memorize each lap time and coordinates, display to the pilot the best and the current lap time, and transmit that info by radio to a laptop, up to 2km away, on the pitbox. This is the starting point of the device and I would like to make it a reality. For the near future, I have more ideas to evolve it.

My experience with electronics and programming is very basic, but I see, in this gadget, the additional motivation to grasp arduino "lego like" hardware and programming.

I'm hoping to get some construtive feedback about the feasibility of the project. Thanks in advance to all.

Yes, it is feasible subject to actual requirements:

  • With IR, you can get lots of interference from the sun => physical shielding & orientation is important, as is time of day/position of sun vs rx Sensors.
  • it will only detect one time if a group finishes together
  • Using optics will help focus the beam.
  • A low power Laser beam could be an option to consider.
  • you need to decide what resolution of timing you need (how fast is the travel etc)
  • xBee/Zigbee is good but they may be cheaper alternatives available with longer range. You can get long range ZigBee, but @ 2km you will need very good antenna design with RF.
  • What happens if someone wants to 'jam' your RF or even the IR....or if you lose RF contact intermittently.
  • for the IR look at the TSOP4038 (light barrier), which is probably best IR Receiver for this application.
  • make sure there is battery backup if running anything off mains power.
  • Consider RFID or active RFID.
  • Just to repeat.... you need to be 100% sure of accuracy, resolution, reliability, repeatability of time measurements & calibration requirements before the project begins.

In summary, 'do-able' but typically requires lots of trial & error to get it right.

AnalysIR brought up some good points. Here are a few additonal considerations.

  1. What is your required accuracy?
  2. Are there going to be multiple vehicles (or whatever) on the track?

The answer to these questions will determine whether or not the use of GPS and IR/laser sensor will be sufficfient.

If there is a single vehicle, an IR/laser will be sufficient, and will provide better accuracy than GPS, which will then be unnecessary.

If more than one vehicle, you are restricted to the accuracy of the GPS. Why? Because you won't know if another vehicle broke the beam to the light sensor. The consequence of this is that the light sensor becomes useless for anything other than detecting a "start" condition, and then only if the beam can be pointed in such a way as to detect ONLY the vehicle being measured.

So, let's look at GPS as a measuring device for this purpose. You speak of trigglering only by one coordinate. This would be fine if the track is not a closed loop, and if other parts of the track do not cross the starting value of the coordinate being measured. (oval, circle, 'S'-shaped, etc.)

So, you will need to check two coordinates. One can be single coordinate, and the other will need to be a range of coordinates. Assuming your coordinated are, for example, a single longitude (say 82.00000), and a range of latitudes (say 42.01344 to 42.01339), this will give you a position somewhere on the start/finish part of the track( assuming that falls within the latitude range), at a particular longitude. You can, of course, use a single latitude and a range of longitudes. Alternatives could be (1) a single coordinate that you can test for being between the start/finish line and any other part of the track, or (2) a continuous measure of speed, and calculated distance traveled, which could be used to tell if the vehicle is approaching the line.

The next place you run into problems is if the start/finish line is not oriented exactly north-south or exactly east-west. So in this case, you would need to calculate the arrival at a box or a single line that defines the finish line.

As for GPS accuracy, a single, fixed GPS that is near the start/finish line and that can provide error signals to the vehicle or to the receiving station, would considerably improve the accuracy. After all, you don't need absolute position, only positions relative to the start/finish line.

Sounds like an interesting project, and is definitely challenging.

IR lap timer

GPS lap timer

Hi. I'm sorry for the late reply.


The accuracy and the resolution ideally and to have a starting point would be on the tenths of a second. The reliability and repeatability of the measurements would relly more on the light barrier and less on the GPS time. Even if would depend on the GPS, I think that the difference would be on the tenths of a second. This is perfectly acceptable to me, because is at amateur level. It's for trackday riding. When you recommend the TSOP4038 and speak of a light barrier, I would need to put several of these inline? And how would I distinguish from any other light barrier? I was thinking on putting the light barrier on the pit wall and the receiver on the bike? Would a laser like this one be a better choice? (


I thought about what you wrote, and as I've writen above, I was thinking to put the receiver on the bike with the arduino and the GPS. That's why I need to have a radio link back to the pitbox by radio. The light barrier on the pit wall would then be able to be used by other bikes with the same system. The idea of using the GPS, besides lap time measurements, it would be used for trajectories analisys, and partial times measurements. I are right when you say that I would ne a range of coordinates, so my next step is to determine the track orientation, and to figure it out what are the range of coordinates that I'm going to need. If the track is skewed relatively to longitude and latitude, I'm going to need a range of coordinates on both orientations.

So for the Bill Of Materials, I need to buy the GPS and the IR/laser? And for the radio link? What would it be a better alternative to the ZigBee?

The track that I usually go is the Estoril racecourse (N 38º 44'58.09" ,W 9º 23' 26.87")

I am not familiar with that laser, but based on a quick review it seems fine.

Assuming a finish speed of 40 Km/hour one tenth of a second equates to just over 1m travelled in that time. So in theory another user 1m behind could finish at the same time. (Hope my calculations are correct!).

If the receiver is on the bike then I would think the IR led is better. If the receiver is fixed then the laser should be better. You need to match the receiver to the wavelenght of the emmitter. The IR Led will have a different wavelength from the (visible) Laser.

If multiple bikes are finishing together you need to consider that one might be obsured by the other.

I cant imaginge how you could easily arrange multiple beams/receivers at the same loaction with multiple receivers located on one bike.
However, if the receivers are fixed it would be possible to arrange that with IR & Lasers.

Have you considered if dirt/muck will get onto & obsure the receivers?

If you have GPS onboad and its active, you should use it to sync time every few seconds (or just at the start & end of each race), which will give you pretty good timing.

Your other questions just require use of a good search engine…

Overall, it sounds like you are on the right ‘track’ and ready to move on to prototypes.

Thanks for the input to all, and particularly to Analysis for that last one.

I already bought an arduino, gps and LCD from a Nokia phone. If needed, I will be in the prototype forum.


Hy everybody ! I have started the same project in september 2014. In my project i used only GPS to check the lap time and count the laps. Recently i decide to transform it in an open source project, so i put all the complete code on Github. @DHeart, if you want, you can view the project at this url:

In the wiki you can read some information about the project. At this time i'm able to compile the code only with Arduino IDE 1.5.6 (with the new IDE the compiled code freeze).

Tell me what do you think about it and, if you want, you can join the project.