Crossing a metal line

I have a go kart (electric) that goes about 20 mph I have a track setup in a warehouse and I want to put a timing system in. I'm thinking I want to put a metal strip down in the track and use some device that will pick up the metal strip as I cross it and the arduino can write it down on an SD card or transmit it (thats an issue for later).

any ideas how to make that work ?

(it would be sweet if I figure out a way to put in multiple strips so I could get a time at different sections of the track)

Or a light source and a photoeye/photo Detector. Detect the cart breaking the beam.

The problem with a photo light source is if I get a 2nd car (to race) then if both cars cross at the same time (or even close) the 2nd car would "miss" the line

pump AC or pulsed DC through the wire (so it generates a magnetic field) and use a Hall Effect sensor in the go kart’s Arduino? Actually I suppose you wouldn’t need the wire…a strip of magnets would work too (although then you’d have the problem of it attracting detritus over time).

If your go cart is moving with 20mph, it is about 9m/s, relatively fast. Most hall sensors have around 0.1ms response time or maximal switching frequency 10KHz. I use them for my POV displays and have to use a longer magnet from Radio Shack when I rotate the POV at say 5REV/s at 0.25m distance (~8m/s). You have to get that magnet too and make sure you have the sensor close enough.

Wont the metal strip mess up as well if two cars pass at the same time? Perhaps multiple ir setup,
or even a few flattish ir detectors and have ir leds on the button of the car, maybe even each car emmitting a special pattern fast enough to be read while passing and still get enough data to decipher which car it was
or flat as you can get reed switches on the ground, or simple pressure detectors of some sort

I am most of the way through a very similar project. I am using Infra Red to generate a coded signal representing the car, my application is for personal use so I am only interested in tracking a single car (RC or Go-Kart) however I am building it in such a way that I could track more than one if I needed to in the future.

The key challenge is how to capture the IR signal from more than one car and the answer is very simple - point the IR Transmitters up and string a line of sensors above the track. This approach works very well for the commercial lap timing system that we use in our club for racing model cars.

I am building my system so that it can be used in two applications

  1. Timing my RC Cars - in this application the transmitter is fixed to the car, the receiver has a lap time display, indicator LEDs and a buzzer that signal whether the last lap is faster or slower than the previous laps. I can leave this somewhere where I can see/hear it while i drive the RC Cars.

  2. Timing go-Karts - I used to race go karts, but stopped because I got frustrated that I had no feed back on different lines around the circuit until after I had finished the race. I am keeping the my lap timer project as small as possible so that I can strap it to the steering wheel of a club kart and get in car feedback on lap times. To do this I would fix the transmitter to the pit wall - the lap timer cant tell whether it is the transmitter passing the lap timer or the lap timer passing the transmitter.

I will start putting some details up on my blog over the weekend.

Duane B

You could put the timing and sensor in the cars. And what to sense? I dunno if it would work for you but a buried -unshielded- cable with current running through will make a field that a latching (security type) Hall sensor can detect and trigger a digital pin in a lot less than 1 millisecond. They make those especially sensitive to work with weak magnets.

You could set up a very bright overhead light with aperture/shade so it makes a line of light from overhead that will cause a light detector to change state. That could take some work tuning to not trigger for the regular lights, just when the extra bright finish line light is detected.
If you could make a finish line that was lit up then a light sensor under the car would probably have no difficulty finding that.

You could use ultrasonic receivers inside the cars, ultrasonic beam is very directional.

I like the idea of a hall effort sensor and a wire loop ... I've already been working on getting speed information from the kart

I've need used a hall effort sensor and looking at wiki ... it seems like I could put a couple wires down and count how many I go around to get a couple different positions throughout the track

There isn't any other way to encode data in the loop is there ?

the idea is the arudino in the car would be transmitting its time and other information the entire trip and as soon as it crosses the loop it would tell the timing computer its at a "checkpoint" ... it would be nice to have a couple "checkpoints"

I like the idea of a hall effort sensor and a wire loop

Forget the hell effect sensor but go with the wire loop. Pump about 125KHz through it and have a coil on the cart. When it passes over the loop it will receive a signal and use that to time the car. It is a bit like RFID only without the ID part.
You could even have different loops going at different frequencies to differentiate different parts of the track.

Conversely you could put the emitter in the cart and have the track loop pick it up. Then the electronics in the cart would be a simple oscillator and all the smarts could be fixed.

The IR Approach is seriously easy although the commercial track I used to race at used a buried cable system.

Duane B.

I understand the IR solution ...

the loop and coil thing is above my head but the concept sounds good ...

any one know what to google to read more about that ?

Start reading about induction.

Might not be what your looking for, but you have to admit its cool to have your lap time on the steering wheel and also be able to turn the same system to timing radio controlled cars if you wanted -

My work in progress RC/Go Kart lap timer -

Duane B