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Topic: wireless xbee Ardunio network timing of mountain bike race is this possible? (Read 6564 times) previous topic - next topic


Below within quotes is my original post under the topic "RFID conundrum for start / finish line timing of mountain bike race".  Instead of creating a new thread I have chosen to modify the title of this one. 

I am now proposing,
An Arduino Uno at the start connected to an Xbee, ID-12 RFID reader and a photoelectric switch.
An Arduino Mega at the finish connected to an Xbee, 3.2inch TFT LCD module with touch panel & SD card cage, ITeadstudio ITDB02 Arduino Mega Shield V1.1 for LCD Module & DS1307 RTC, ID-12 RFID reader and a photoelectric switch.

At the start a rider would first scan an RFID card to identify themselves then they can pass through the photoelectric switch onto the course which will start the timer.  At the finish the rider will first pass through a photoelectric switch and then scan their RFID card to register the time recorded as their own.

The Arduino at the start would only need to transmit the RFID card value and switch state to the Arduino at the finish.
The Arduino at the finish would be responsible for everything else...

Does this sound realistic or is it back to the drawing board again?

Thanks in advance for any input, Jason

Hi All,

  I am currently working on a downhill mountain bike race timing system based on a Mega 2560 with a real time clock and an lcd display.  The Ardunio will be located at the finish line and will be directly connected to an RFID reader and an Xbee.  Connected to another Xbee will be another RFID reader located at the start line.
  The problem is I dont know how to spec the RFID system for my application.  Ideally the antenna would be contained in a 2m x 0.5m mat and the system would be able to read Tags upto 0.5m above the mat that are travelling at a velocity of up to 10 m/s.  It would only have to read one Tag at any one time.  All I have seen in relentless googling is complete turn-key timing systems for huge amounts of money.
  Thank you in advance for advice or suggestions, it will be very much appreciated!



Ideally the antenna would be contained in a 2m x 0.5m mat and the system would be able to read Tags upto 0.5m above the mat that are travelling at a velocity of up to 10 m/s.

This is not the sort of thing you could do with a normal passive RFID system. The range is too large.

You might try and look at active tags, those have small batteries in them that last about three years. And yes they are an enormous amount of money.


Thank you for your reply.

I have recently discounted passive tags as the propagation delay would also make them unsuitable at 10 m/s would it not?

How expensive are we talking about and do you have any links to a suitable product?



Norbane are suppliers of RFID stuff.

The products you want to look at are the long range readers and the hands free readers.

IoProx proximity long range reader, SI-HF500 hands free reader

I don't know prices but I would guess in the £300 - £800 region.


Ah that is quite pricey when I was initially looking at simple passive card reading kit for say £20!

Do you know anything about commercial systems like championchip as they use passive tags?



Yes but championchip requires the tag to be on the shoe and therefore the read range need only be very small.
With a passive EM RFID tag you can only get a range of about 12" if that. That is what all the low cost RFID readers are. I used to design RFID readers for a living.

To get greater ranges with passive tags you have to go to UHF readers and they are very expensive.


I used to design RFID readers for a living

Then you are certainly a good person to talk to and I think you for taking the time to respond.

As I know next to nothing about this, is it possible to use a battery activated passive tag with any low cost passive RFID reader or do they require specific hardware?  Assume that a read rage of 12" (30 cm) is workable would it also be possible to read a chip that passes over the antenna at 10 m/s ?



a battery activated passive tag

If it is battery activated then it is not a passive tag, it is an active tag and we are back to those hands free readers.

The cheapest RFID tags operate at a speed such that it takes about 50mS to read a tag. At a speed of 10m/S the active read area has to be half a meter for the tag to be in the field long enough. That is way too much for a passive tag, I think you will struggle to do this with low cost technology.


Back to the drawing board then!

Can you suggest any other technology that will let me uniquely track individual riders as they cross the start and finish lines?



The fact that there isn't a commercial system to do this (is there?) probably tells you there is not a simple way of doing it. How about a 2D bar code on the vest and a photograph at start and finish?


Well there are championchip, ipico etc but obviously they are shall we say, not affordable.

I would like an automated system and thought using RFID would be pretty simple and not that expensive.  Machine vision was considered a possibility but deemed unsuitable as on a wet muddy course it would end up unreadable by the time the rider finished.

What about something like this? http://www.ebay.co.uk/itm/RF8315RT-u-Active-RFID-8-Meters-Transmitter-n-Receiver-/290365177740?pt=LH_DefaultDomain_0&hash=item439b1cff8c#ht_2066wt_1064


For (car) sprint racing we use a lighting split beam and have somebody read the number off the side of the car to say which car it was. :)

How much separation will there be between consecutive riders? If they are going to be multiple seconds apart, you might be able to get something working by using a simple 'bike presence sensor' (timing beam, pressure pad etc) to give you an accurate time, and a short range transmitter on each bike that just keeps broadcasting "I'm number seven" (or whatever) over a range of a few yards. If your bikers are going to be crossing the line close together I can't see that working, but if they're coming through separately you might be able to get something to work.

Alternatively, for multi-lap races we often use active transponders and a beacon - the hardware is quite expensive to buy but you may be able to rent it - people who have splashed out on this sort of thing may be keen to recoup some of their costs?
I only provide help via the forum - please do not contact me for private consultancy.


short range transmitter

Please elaborate as your suggestion sounds entirely feasible.

It works like this, Riders start at the top of the hill and race down the course one at a time to the finish at the bottom.  A really short course would take a fast rider approx 30 seconds to get down but a slow rider on the same course may take 90+ seconds.  Rider starts are staggered by 30 second intervals so although it would be bad practice to send a slow rider down before a fast rider it is still feasible that there would be 2 or more riders on the course at any one time and they could finish in a different order than they initially set off.  Riders would typically cross the line separately.

That's it in a nutshell.

Initially I had planned to wire a infra-red photoelectric switch into a motorola walkie talkie as the push to talk button to trigger the vibrate function in a receiving walkie talkie wired into an arduino and start a timer.  At the finish would be another photoelectric switch connected directly to the arduino that would record the time.  While this would work it seemed somewhat crude and a waste of the hardware, also it would only allow one rider on course.  RFID seemed ideal for the project until I found out the cost was significantly more than I first expected!

Any suggestions?  Im all ears!




Original post modified to reflect new direction of project.

Thanks for any input!



Does this sound realistic or is it back to the drawing board again?

I guess I fail to see the solution here. Are the racers racing each other, or the clock? If they start at staggered times, more than one rider at a time may reach the finish line. Lining to to scan RFID tags to stop the clock hardly seems like a viable solution.

How is sending the switch state going to prove useful? What you need to send is the RFID tag and the time that the switch was triggered. That defines the start time for a particular rider.

The end time will be defined when the rider scans his/her tag again. Getting them to not pass each other on the course, and to line up neatly at the finish line will be the biggest challenge.

It's back to the drawing board, I think.
The art of getting good answers lies in asking good questions.

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