# Proximity sensor with memory

#### joerenfield

Joined Nov 21, 2011
3
Hello,

I wold like to know if exists a way to register times and id on passing bicycles (individually) in a road by a proximity sensor and keep those times in memory to be able to be sent or downloaded to a computer later.
Maybe fitting an individual transponder in each bicycle to identify them.

Thanks!!

Josep

#### colinb

Joined Jun 15, 2011
351
Sure, there are many ways to do this. Are you looking for a design, or to buy an off-the-shelf product?

#### joerenfield

Joined Nov 21, 2011
3
Off the shelf if possible, but all options may be ok.

#### colinb

Joined Jun 15, 2011
351
I know there are many commercial off-the-shelf (COTS) products for race tracking. Local cycling and running races use ankle-mounted transponders to track competitors and precisely log finish times.

My personal expertise is in the area of custom wireless solutions, however, and I don't know about the specifics of race tracking systems.

#### joerenfield

Joined Nov 21, 2011
3
let me explain our goal and see if you can figure solutions.

We do race timming, we can have up to 70 participants that will be
racing through road stages. In each stage we put 2 to 5 intermediate
time controls that need to be recorded to be recovered on a computer
later.

When the participants arrive to end of sector (3 to 5 stages) we would
need to dump the times into a computer.

Then the participants would start next sector and so on.

Dumping times can be via 3G or cable.

#### colinb

Joined Jun 15, 2011
351
The issue that would concern me the most is getting precise time/location captures at the checkpoints and finish line. If you are using radio communication, how do you know when the competitor's transponder is crossing the finish line? The simplest way to limit communication distance is to reduce transmitter and/or receiver power or gain. However, the resulting precision of communication range is very poor. The competitor could be 3 feet from the receiver when the transponder signal is received, or he could be 30 feet away, depending on orientation of the transmitter, obstructions such as the person's body and bicycle, other competitors' bodies and equipment, etc.

Race transponder systems use other techniques to more precisely limit radio communication range. Some use a loop buried in the ground at the finish line, which has a directional and localized electromagnetic field so that transponders are identified quite precisely.

The Wikipedia article mentions some race transponder systems. Google will help you find others. I have no idea of the cost, but the tags are surely very inexpensive (often disposable). However, the rest of the system is likely to cost some significant \$, I expect. If the competitor transponder tags use a standard LF or HF RFID technology like 125 kHz or 13.56 MHz, then you might be able to build an inexpensive reader and be able to take advantage of cheap off-the-shelf RFID tags.