Tips on transponder types (BLE, RFID or something else)?


I’m about to do start a project where I will build a laptimer for off-road motorbikes, and I’m trying to find out what kind of hardware I could use for identification of the bikes.

The case looks like this:

  1. I want to get inidividual laptimes from multiple bikes at a given checkpoint of the track.
  2. The bikes may be dirty, so IR sensors are not applicable.
  3. The bikes will travel at a speed of maximum 20km/h when passing the checkpoint.
  4. The bikes will pass the checkpoint with a distance of roughly 2-4 meters.
  5. A timing accurancy of ±1sec is accepted.
  6. The system will be built with a main unit at the checkpoint, and with some kind of slaves/tags/transponders on each bike. The laptimes will be displayed only at the checkpoint.

Anyone having any suggestion on what kind of hardware that would be suitable?
I first thougth about RFID, but as far as I know the range of RFID is to short?
IR is not an option due to the fact that the bikes may be dirty.
BLE may be an option but I’m not sure and I can not find transponder/tags to put on the bikes when I’m searching at google.

Interesting project.
I see a problem, however. If you rely on the motorcycle transponder to connect to a receiver and pass data in a matter of one second- what do you do when the connection is not made? WiFi might be responsive enough for a garage door opener to recognize a car in the driveway, but not to link to a passing motorcycle.

RFID modules like the inexpensive RC522 module has a range of about 1 cm, so toss that solution outright.

I have zero experience with Bluetooth- I don't know if a Bluetooth device would connect fast enough for this purpose. And if it is, you would have to pair every bike with the receiver. I do know that old-school Bluetooth connects faster than BLE.

The transponders on our cars for toll collection are read by microwave transceivers at the toll collection point, but that is likely out of your budget.

You could put a GPS receiver and a LoRA transmitter on each bike to constantly feed location data to a central computer, but the low data rate of LoRa might not update the position often enough for the checkpoint accuracy you want.

I'm out of ideas....

Most of the basic RF modules you can buy for use with Arduino, using 433MHz or 2.4GHz, will have enough range. Can transmitters on the motorbikes be powered by the bike battery? If so, maybe they can just send out a unique code at, say, 1s intervals. An ir beam could be used to detect exact time of the bike passing the checkpoint (doesn't matter if the bike is dirty for that to work).

But what if two or more bikes cross the checkpoint together? Can that happen, or are the starting times staggered for each bike?

There are RFID readers that can read tags at a distance - fifty feet or more for some of them. They tend to be expensive though. Zebra and Trimble are brands you can look for.

This one works at 3.59 MHz. It says "inductive" so presumably there's a transmitter/receiver coil at the finish line.

It would be possible to feed the transponder with 12v from the bikes, but as I want to build the system independent, and be able to use the system on different motorcycles from time to time it would be a bad solution.
It's fully possible to narrow the track width at the checkpoint for the laptimer. That would give the system to positive effects:

  1. The bikes will pass at a slower speed to be easier to detect.
  2. There will not be enough space for two bikes to pass at the same time.

The MyLaps-system your linking to is a very nice system, but very expensive. This have tall the functions I'm looking for and more. That is the system that are used for most professional competitions, and most dirtbike riders have their own transponder from mylaps.
What I want to do is to a more simple copy of that system for laptiming at training. The absolutly very best solution would be if I could build a laptimer computer that could read the MyLaps transponderns, but I haven't found any information of how to read and identify them.

How much money are you prepared to spend?

If you only have a handful of riders, then for each rider you could use a pair of cheap low power, narrowband radio transceivers, one on the rider, the other at the finish line both set to the same RF channel number.

Each additional rider gets their own pair of transceivers set to their own unique RF channel number.

Adjust the transmit power so that each pair is only able to communicate when they are close together.

Use an Arduino to continuously query the stationary transceivers at the finish line to log when they make contact with their mobile counterparts.

Cheap 433 MHz transmitter on the bike sending out its ID continuously (and very frequently); receiver with directional antenna or shielding at the finish so it only picks up the signal while the rider is crossing the finish. The limited range of those transmitters becomes a feature here.

Of course you have to make sure the covered area by the receiver is big enough and transmission frequency is high enough to be guaranteed to receive the transmission at least once.

Ok, what if we combine these ideas? An ir or laser beam is broken by a bike passing through the checkpoint. The checkpoint immediately sends out an 433MHz RF signal. The bike circuit, powered by 2 or 3 AA or AAA batteries, receives the signal and send out a response with the unique code for that bike, possibly repeating a few times to ensure reception. The checkpoint receives the code and logs it along with the exact time the ir beam was broken.

This means neither circuit is transmitting continuously, keeping battery life long enough for a day's use. The 433MHz receivers consume only a few mA.

@mikb55 The question of how much money I'm ready to spend is a little bit tricky. If I find a good working solutions that is easy to use and works well and the transponder works well in dirty conditions I'm ready to spend up to roughly €1.000.
For a crapy solution that wouldn't last and work for a long time i guess the limit is €3-400.
The solution with individual transponder and receivers for all bikes are not a solution i want to go for. Not good enough.

@wvmarle Sounds like a good solution. Do you have a link to a suitable product that I could buy that works well with arduino?

@PaulRB There is no need for a battery life of the transponder longer than 3 hours. And the accurancy with the IR-beam is not needed either.

@wvmarle Sounds like a good solution. Do you have a link to a suitable product that I could buy that works well with arduino?

Lots of such transcievers around. You could go cheap and primitive with a receiver/transmitter pair such as these; or more fancy with an RFM69 or HC12 module. The latter are much easier to work with, especially in this situation.

The hardest part would be the antenna: the module on the bike would be omnidirectional, the receiver shielded so it can only receive transmissions in a very narrow cone: the finish line.

@wvmarle I looked at the link you sent and if I understand this right thoose are modules that you have to attached to an arduino and supply electricity?
I guess that the enviroment for the transponder at the bike will be the crucial part for a transponder like that. The transponder will be exposed for continuosly vibrations and shocks and have to be encapsulated to withstand water and dust (at least IP66).

All require power. There are no doubt beacon type of transponders that don’t need an Arduino (such as the toll gate tags mentioned before), I have no experience with those.

Lots of interesting answers, but none look at the problems of what if two or three bikes pass the checkpoint at the same or nearly the same time, and they are gone in a few milliseconds. There is no way that Bluetooth would connect that fast. 433 might work, but you need something to encode the bike ID into the 433 data, meaning an Arduino or similar microprocessor on each bike. Again, what happens when three bikes pass the checkpoint within milliseconds? You could consider a GPS/LoRA combination so that you could "see" the bikes all along the path, but precise checkpoint detection would still be a problem.

I don't know how fast these readers respond to a transponder, but you probably would need to add another zero to your budget.

@SteveMann Like i wrote earlier there is a possiblity to narrow down the track at the checkpoint, and this would make it possible for only one bike at a time to pass the checkpoint, and it would also be possible to lower the speed of the bikes down to maybe 10km/h.
But just as you say, it may be impossible to identify the different bikes without a microsprocessor on every bike....

I put an order on thoose yesterday:

I think there may also be another problem with the 433 RF solution, and that's the range of the transponders. When I look into the data sheets it seemes like the signal has a little bit to long range, and I'm worried that the reciever will pick up the signal to early. Hopefully this will be possible to solve with some kind of shield around the transponder.