Infrared/Laser Trip Wire

Hello everyone,

I am looking for some insight on how to continue with my project. Here is a brief overview of what I have so far.

I am making a portable drag racing tree using my arduino uno. This will be used outside and on dirt and with diesel trucks, so basically it will be subject to sun/shade, dust, and smoke. Two trucks will line up at the starting line (designated by me), I will start the light with my remote, it will cycle thru red, yellow, and then they will leave on green. This part works extremely well, I am using a wireless remote and dont employ any "delay()" in my code, it is all done using millis().

The next step is to add a trip wire to tell if one of the trucks jumps. I first tried simple photo resistors in the middle of the track (inside of a box with 1/2" holes on each side to block out ambient light). In my garage this worked really well, but as soon as I took it out this weekend to use it, it fell flat on its face. It was extremely hard to get the lasers lined up from 20+ feet away in the daylight (I can definitely come up with a better way to do this tho) and as the day went on and the sun went down it messes up my calibrations for the photo resistor. Long story short the laser and photo resistors were not reliable enough to continue on this path.

I have been reading up on the forum here on maybe infrared sensors and an infrared LED. Im thinking TSOP4038 and TSAL6200. But here is the next problem, I can only send power to either the middle of the lanes (lanes are side by side) or the outside edges. To be able to send power to both sides of the track and the middle would be too much wire to put down and clean up and trucks would be running over it.

So here is my question, could I put an emitter and a receiver right next to each other in the middle of the track? And maybe have them hit a mirror on the other side of the track? If i did this, could the emitter reflect off of the truck and give a false reading? Is there other options?

Any help is much appreciated, as well as other ideas.


The emitter doesn't need much power, so a couple batteries in a standalone circuit (all you need to do is create a 38KHz blink of an LED - can do this with a 555 timer or ATTiny) would work fine. With an IR LED, a mirror, and a lane width of no more than 6 meters you could probably keep everything on one side, but you do have the problem of a reflective car acting like the mirror as you mentioned. It's much more foolproof to have the emitter on the other side. Perhaps you could have the IR receiver mounted about a meter higher than the emitter to prevent reflections off the cars.

If you use a laser module with a focusing lens (so you can "unfocus" it) it's much easier to hit your IR receiver target. Any cheap, red laser will have more range at lower power than an IR led.

The TSOP4038 became the TSSP4038. Make sure you keep it shielded from direct sunlight.