Ideas for a lap counter for RC cars?

Hi,

What about optically? Put some time of simple 'bar code' on the bottom of each car. Read it with a reflecting type ir emitter/detector and decode the pattern data in the computer.

Put some type of simple 'bar code' ....

-- Luhan Monat (luhanis 'at' yahoo 'dot' com) "The future is not what it used to be..."

Good idea, Luhan! Let the bar code be the "clock". Can a PIC or CPU handle the interrupts quickly enough to establish "pecking order" at each lap... if several hit simultaneously?

...Jim Thompson

If the 'bar code' is simple enough (maybe 6 bars) the timing is somewhat easier. I'd say a 20mhz PIC would have no trouble. The que idea looks good because there is a lot of 'free' time between readings.

Most likely. At 1000 inches per second (a plausible maximum speed for a slot car these days, apparently), 0.01" is 10 microseconds. It should be possible to handle, say, 4 lanes with that resolution even using polling with a micro with a 100ns instruction cycle (eg. a 40MHz

Best regards, Spehro Pefhany

I am going to read the link you sent Paul..thanks.

Here are some more ideas I found searching for the article Michael mentioned:

Hi Joe,

We worked on an RFID system a few years ago for a local store owner who believed the system was not detecting some tags.

What we found was the 6 or more tags in the same bag with one tag in the patrons pocket would fail to detect all the tags. The result was collisions and some tags are not detected.

We reported our findings to the store owner and he followed through with some RFID people.

Older RFID tags have collision problems. Newer tags have a globally unique digital signature and transmit twice, both transmit times are random so there is little chance of a collision. RFID is probably the answer, an RF source to power the tags is easy to build, the receiver is a little more difficult but easily doable. The tags are small and don't need external power, and your local Wal Mart and or your local record store has an endless supply.

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As luck would have it, I also design low power photonics. I don't know how big your cars are and how wide the finish line is though. If the cars are small, even the simplest transmitter is probably to large and the coverage of the transmitter and field of view of the receiver can be a problem too. An LED transmitter would need the same type of anticollision provisions built into it as the RFID systems have.

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There is a third possibility if the cars are large enough and have dc power available to power a transmitter. That option is to use a Hall magnetic detector and transmitter in the car. As the car passes over magnets in the race track, it sends out a unique identifier code to the receiver located at the computer. Lynx makes the 433 Mhz transmiter chips that use SAW devices to set their operating frequency. You would need a unique identifier generator chip (Maxim and others) and some anticollision measures too.

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A note on anticollision technology...... You don't need a James Bond secure and accurate system. If you have a capacitor charge to determine the first transmit time and the discharge to determine the second transmit time, you end up with 2 random signals. After all, you aren't trying to time supersonic aircraft and a few milliseconds error is probably acceptable.

Regards,

Mebart

But the flag weight and wind resistance is not trivial, especially on smaller cars. Even the lightest weight flag and flag pole will affect handling in tight corners. I'd hate to be the unlucky one who has to use the highest flag.

Also, it's limited to a max of six users. What if number 7 comes along and wants to race in place of racer number 5? Each car owner needs an assortment of flags and needs to be able to change them easily.

It looks fine for 2 or 3 racers on an home track, but for larger scale exhibitions and events, the system has problems.

Good luck.

Mebart

A co-worker races people-controlled cars in the SCCA and has recently talked about some kind of transponder system they are using for lap times. I can't remember if it's RF or infrared. Each car has a relatively small and inexpensive transmitter, and I think the receiver(s) plug(s) into a laptop. This is off-the-shelf stuff. In your case, though, the weight of even a small transmitter might be objectionable.

You might look into "RFID" tags. The idea here is that there is a small, cheap, passive tag that gets stuck on the can of beans or toy car or whatever, and a reader that sends out a burst of RF that energizes the tag and causes it to transmit its serial number (or whatever) back. I think you can get these that work over relatively short distances, so the reader at the finish line won't count cars on the other side of the track.

The barcode idea might work for slot cars, but I think you are talking about cars with rubber tires that don't run on a fixed track. You might be able to make the barcodes work IF the finish line is maybe only one car wide.

Maybe you could put racing numbers on the top of each car (say a 2" white square with 1" tall black numbers in the middle), hang a camera over the finish line, and apply OCR to the digitized pictures.

For the RFID, bar code, or OCR ideas, you could shoot an infrared beam across the track to decide when to turn on the RFID reader / turn on the scanner / take a picture.

This can happen. The trick is to select frequencies that don't add up to one another or are harmonics (2x, 3x, 4x, etc) of one another. Look up the frequencies for Touch-Tone (tm) phone dialing for an example.

One thought... with any system like this, you will probably be able to count laps fairly easily, but lap _times_ will be harder. To count a lap all you need to know is that the car got close to the line; to do timing you have to know exactly when the front edge (or whatever) of the car passed the line, which is trickier to detect, especially if two cars can pass the line at almost the same time.

Matt Roberds

I was going to build something similar to

Looks fairly easy to do

Paul

Curcuit Cellar published a construction article on such a system (for mud bikes, IIRC). Sorry, I don't remember issue# or date. Within the past 5 years, I would guess.

Un bel giorno Joe G. digitò:

IMHO the easiest solution for a good precision is to put a magnetic stripe on the finish line, detect the passages with an unexpensive sensor mounted on each RC car (just like go-karts), and send a short RF burst to the fixed station at a different frequency for each car. On the fixed station you can use various ways to detect each burst, for example a module that "scans" your range of frequencies: the modules studied for frequency hopping applications are very fast in switching carrier frequency (tens or hundreds of us), look for example