Looking for suggestions on autocross timing system


I’m trying to build a system that will provide timing for autocross events. I’ve got two arduinos with xbees, one pair each for the start and finish lines, connecting to a web service via connectPort. So far, so good.

What I’m missing is the trip mechanism. I’ve been testing infrared, but have not found any emitters / receivers that are strong enough to cross the road (No chicken jokes, please). So first question, could someone recommend a emitter / received pair for the job?

But even if I get an infrared beam across the road as a timing trigger, I’d need, I believe, two arduinos at each timing gate: one to modulate the IR on one side of the road, and one to receive it and transmit via xbee on the other side of the road. (I see I could use a timing circuit to modulate, but I think thats beyond my skills.) So, could there be a way to set up a trigger mechanism that only uses one arduino? For instance, could the IR emitter be so powerful that the car passing it would reflect the light back into the same arduino receiver? (I feel foolish asking this, but seeing as how my home stereo remote IR bounces all over the room, I thought it might be possible).

Lastly, I wish there were some device I could attach to the cars that would identify the car as it made it around the course. Right now, if for some reason either the start or finish gate does not register a time, and because the times are not tied in any way to a specific car, a missed trigger or errant trigger will cascade through the service and is difficult to correct without lots of re-runs. But, if I could tie each trigger to a specific vehicle, it would be easy to see if a vehicle was missing a start or finish trigger. So, would there be a practical and inexpensive way to “tag” the cars? (Typically there are ~50 cars participating)

I appreciate any input!

There are several versions of laser “trip-wires” on Instructables, for example,

As for tracking individual cars, you might try looking into DIY versions of racing transponder systems. Now that I think about it, the RFID-based systems they use for marathon runners might be a better way to go.

Thanks, Pantaz. I'm a bit leery of a laser trip as the small laser point can be difficult to line up with the receiving photo resistor in the autocross environment. Thats why I'm hoping an infrared system might work which could provide a little more ease in setup.

You could do it with IR using the TSSP58038 IR Receiver Module for Light Barrier Systems from Vishay + TSAL6100 (narrow beam)

It is possible to get very long distances from IR, but 5->20m would not be hard.

To get it all on one side of the track (tx & rx & 1x Arduino), use a reflective material on the far side, like a hi-viz jacket/armband or bike reflector.

Then modulate the IR @ 38kHz with on/off pulse of 500->1000 uSecs. (depending on timing accuracy/resolution required)

If you need longer distances you will need to use optics & tubes, which also have the benefit of narrowing the beam and thus increasing accuracy.

Of course this will not distinguish between 2 finishing together!

Make sure you place the rx facing away from the sun & bright lights. Best ot conceal in a dark tube.

You will need to play with it to perfect it.

For the backup option, look into active RFID (essentially a low range RF transmitter with unique ID. You could mock up your own without the need for expensive commercial options, using low cost transmitters (avoid blutooth as you will get intefernce from cell phones). with this it would be hard to distinguish between close finishes & timing accuracy would not be great.

Great info, AnalysIR. Thanks!