Drag strip cronomether

Good night to everyone, me and some friends of mine have the previlledge to be able to rent closed race tracks, and as usuall everyone wants to know how long theirs cars make in the 400m(1/4 mile), and as I’m the geek guy of the group I said that using some arduinos I might be able to make the start lights and the sensors to measure how much time one car takes from the start to the finish, the problem is that I dont really know how to make the sensors, they will need to cover 2-3meters of road, each sensor in one lane, professionals use what looks like a laser and a light sensor, the laser path is interrupted and there goes the clock, then in the final there is an identical assembly that stops the clock.
If I search for photogates nothing shows up, only lab material, can I use laser pointers and some light sensor(hint please), or any thing else, if possible not to expensive :wink:
I’m open for suggestions people.
Thanks in advance.

can I use laser pointers and some light sensor

Yes: I’ve seen at least 2 or 3 threads on the subject in the “Hardware Interfacing” section in the last year, from people who wanted to time Pinewood Derby cars and other amateur races. A forum search ought to turn some up.

I have already searched, everything that comes up is made to model cars, not real vehicles, so their sensing methods dont serve my purposes :frowning:
I had a flash ideia, using photocells from automated gates, they usually have high ranges, so any source for 4 photocells?

I would make a laser trip wire set up.
Laser at one side of the track, solar cell covered from sunlight at the other (connected to arduino’s analog Pin). When the analogRead on that pin falls below a certain value, you know something has passed in front of the laser.

Yep. You can even get final velocity this way too.

issue with laser is that you don’t have a flat front profile - I would assume that your bumper height’s are all over the place with bumps and different car makes. Maybe 4 inches doesn’t make a different for what you’re doing. In bike, house and car racing (and others) they use high speed slit camera’s for that reason because it does - you could also use rfid - you measure off the front x distance for each car with the transponder. Or use contact strips on the ground to pickup the tire contact.

I have already seen photo-cells aimed at the windshield, but 5-8cm of diference is nothing, because both start and finish sensors will be at the same height, so they will be interrupted by the same part of the car, so I dont think its a big problem, and the best cars have 600hp tops.
Maybe the laser pointer plus sensor is the best thing, should I use LDR(I heard that those are pretty slow, or IR(maybe red lasers trip then hopefully :confused: ), or another?

if it doesn’t make a difference (a few inches) then lasers sound like the best.

I sort of looked into it a while back for bike racing - I saw some intresting stuff for horse racing - and what people did to get better times - by pointing lasers or ir remotes a bit before their horse crossed the line to get a better time…

and what people did to get better times - by pointing lasers or ir remotes a bit before their horse crossed the line to get a better time…

Did I misunderstand or did you mean that they cheated by triggering the sensor manually?

And the best part is that I can get the lasers at less than 5$ from ebaym just hope that they dont get busted in customs, now what about the sensors to sense the laser?

And the best part is that I can get the lasers at less than 5$ from ebaym just hope that they dont get busted in customs, now what about the sensors to sense the laser?

To account for wabble room, I’d use small solar cells (they are bigger than photoresistors/transistors… atleast the ones I can get at radioshack). As i mentioned in my first reply, you can use an arduino’s analog pin to measure the voltage they produce.

yes - people cheating to get better times

As I want fast response I may end up using comparators and just triger and interruption, that would be the fastest thing, because adc conversions take a while until they are done(125KHz clock and each conversion takes 13 clock cycles).
Now my big doubt is in really what sensor should I use, photocells are a bit slow I think, but IR sensors shouldn’t detect the red laser, so I dont really know :confused: