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RF Lap Timer ?

Z

zipzit

Jan 1, 1970
0
Looking for some design ideas...

I'm would like to build a lap timer for athletes who travel around on
a short track. Track size is 100M... (entire track floor size is 100 x
200 feet).

--I'm assuming a small device each athlete carries on tight waistband
(like a CD/MP3 player butt pack...)Obviously smaller is better. This
device would then transmit info on laptimes to a base station..

--Finish and start times absolute do NOT matter. The only thing the
coach really watches is lap time splits. These guys change lead so
often in practice who is in first doesn't really matter, its easy to
see who is where. Today's constant stopwatch work the coach has to do
is pretty disruptive. Rather than focussing on the athletes, he is
always watching the watch.

--Track is generally indoors (i.e. likely no GPS... and I'm not into
Pseudolites... although it is an option, I doubt it is cost
effective.)

--Needs to be reasonably inexpensive.

--Must be non-evasive to the track. I can't place cable overhead, or
under the floor. No way, no how. I think that kills radio frequency
Identification (RFID) ideas.

--Lap accuracy should be to nearest tenth of a second. I can wait for
up to two seconds after lap measurement zone for a display. I would
hope to get up to six athletes measuring at the same time. Lap times
should be in range of 9 seconds up to 15 seconds/lap depending on
drills.

The only thing I can come up with is a battery operated weak RF
transmitter, located somewhere along the side of the track. Each
individual unit includes a RF receiver, which looks for a signal
minimum threshold (T). The individual recievers measure lap start
time as (threshold boundary in (i) + threshold boundary out (i))/2 .
Lap finish time (threshold boundary in (i+1) + threshold boundary out
(i+1))/2. I would then send lap time to base station (laptop or PDA
with WI-Fi or Zigbee card...)

In ascii:

*
Athlete * *
-------> --------T(in)-------------T(out)----------->
Path * *

* *

* R *
F
* *

* *

* *

* *
*
RF Source is off track. T = RF Power Threshold * = RF power.

This is an idea I've been toying with in my head. Anybody else have
suggestions?

Many thanks, LB
Temporily in Chicago, IL
 
R

Robert C Monsen

Jan 1, 1970
0
zipzit said:
Looking for some design ideas...

I'm would like to build a lap timer for athletes who travel around on
a short track. Track size is 100M... (entire track floor size is 100 x
200 feet).

I heard that the NY Marathon gave RFID chips to the participants, and kept
track of where they were along with way with sensor checkpoints. It kept
track of time, and all got mapped to a website where you could look up the
times.

Thus, its probably a product you can go out and buy.

Regards,
Bob Monsen
 
K

Klaus Vestergaard Kragelund

Jan 1, 1970
0
Robert C Monsen said:
I heard that the NY Marathon gave RFID chips to the participants, and kept
track of where they were along with way with sensor checkpoints. It kept
track of time, and all got mapped to a website where you could look up the
times.

Thus, its probably a product you can go out and buy.

I attended a 4x5km relay race last year and the stick had an RFID on it. So
it is widely available at low prices. Don't know about the accuracy though

Cheers

Klaus
 
R

Reinier Gerritsen

Jan 1, 1970
0
I attended a 4x5km relay race last year and the stick had an RFID on it. So
it is widely available at low prices. Don't know about the accuracy though

Cheers

Klaus
Have a look at our website www.championchip.com. There are some new
low cost products to be introduced within 6 months. They are not on
the website at this moment but use similar kind of equipment and mats.
Our product are used all over the world for timing athletes, including
NY marathon.

Reinier Gerritsen
ChampionChip
The Netherlands
 
Z

zipzit

Jan 1, 1970
0
Have a look at our website www.championchip.com. There are some new
low cost products to be introduced within 6 months. They are not on
the website at this moment but use similar kind of equipment and mats.

Ugh. Sorry I wasn't absolutely clear. I CAN'T TOUCH FLOOR OR CEILING
ON THE TRACK, NO WAY, NO HOW. YES, I AM YELLING! As I understand it,
because of this, currently packaged RFID solutions are absolutely no
good. I know they make mats, but that won't work in my case. I can't
touch floor (or ice) as the case may be. Does anybody really
understand the mechanics of the RFID. I know there is a transmitter
antenna which sends out a magnetic field, which excites the
"transponder" chip, and causes the chip to send a signal to a receiver
antenna. Because I can have the athletes carry a small battery pack
unit, I don't need the B Field exciter force... What I don't
understand is the mechanism on the signal going back to the base
station antenna. What does this signal look like? Packet size,
digital code, etc... Anybody been here before?

I really want to do my processing on athlete, as opposed to processing
at base station.

Many thanks, and sorry for the yelling.
LB.
 
R

Reinier Gerritsen

Jan 1, 1970
0
Ugh. Sorry I wasn't absolutely clear. I CAN'T TOUCH FLOOR OR CEILING
ON THE TRACK, NO WAY, NO HOW. YES, I AM YELLING! As I understand it,
because of this, currently packaged RFID solutions are absolutely no
good. I know they make mats, but that won't work in my case. I can't
touch floor (or ice) as the case may be. Does anybody really
understand the mechanics of the RFID. I know there is a transmitter
antenna which sends out a magnetic field, which excites the
"transponder" chip, and causes the chip to send a signal to a receiver
antenna. Because I can have the athletes carry a small battery pack
unit, I don't need the B Field exciter force... What I don't
understand is the mechanism on the signal going back to the base
station antenna. What does this signal look like? Packet size,
digital code, etc... Anybody been here before?

I really want to do my processing on athlete, as opposed to processing
at base station.

Many thanks, and sorry for the yelling.
LB.
Communication with low frequency passive transponders has two main
"flavours": half and full duplex. Texas Instruments uses half duplex:
50ms energizing magnetic field charges the transponders battery (a
capacitor) to about 7V, then field stops and transponders sends ID
code 20ms (128 bits code, FM modulation 123 and 134 KHz, 16 cycles per
bit).
Rest of the world uses full duplex: load modulation of the energizing
carrier (about 125KHz). The transponder modulates the resistance
across its LC-tank circuit. There are different ways to encode the
transponder ID, usualy some kind of Manchester coding. The code can be
found as a tiny AM modulation on the reader antenna.

Read range and S/N ratio is better for TI transponders, but
communication speed and price is better for full duplex types.

The antenna you want to get rid of is not only used to transfer energy
to the transponder, it also locates the transponder within about 1
meter. If you have a read range of 10 meters, where is your precision
comming from? You'll need a UHF communication system to get long
range. More than a few meters is not possible using lof frequency.
Success,
Reinier
 
C

Charles Edmondson

Jan 1, 1970
0
zipzit said:
Looking for some design ideas...

I'm would like to build a lap timer for athletes who travel around on
a short track. Track size is 100M... (entire track floor size is 100 x
200 feet).

--I'm assuming a small device each athlete carries on tight waistband
(like a CD/MP3 player butt pack...)Obviously smaller is better. This
device would then transmit info on laptimes to a base station..

--Finish and start times absolute do NOT matter. The only thing the
coach really watches is lap time splits. These guys change lead so
often in practice who is in first doesn't really matter, its easy to
see who is where. Today's constant stopwatch work the coach has to do
is pretty disruptive. Rather than focussing on the athletes, he is
always watching the watch.

--Track is generally indoors (i.e. likely no GPS... and I'm not into
Pseudolites... although it is an option, I doubt it is cost
effective.)

--Needs to be reasonably inexpensive.

--Must be non-evasive to the track. I can't place cable overhead, or
under the floor. No way, no how. I think that kills radio frequency
Identification (RFID) ideas.

--Lap accuracy should be to nearest tenth of a second. I can wait for
up to two seconds after lap measurement zone for a display. I would
hope to get up to six athletes measuring at the same time. Lap times
should be in range of 9 seconds up to 15 seconds/lap depending on
drills.

The only thing I can come up with is a battery operated weak RF
transmitter, located somewhere along the side of the track. Each
individual unit includes a RF receiver, which looks for a signal
minimum threshold (T). The individual recievers measure lap start
time as (threshold boundary in (i) + threshold boundary out (i))/2 .
Lap finish time (threshold boundary in (i+1) + threshold boundary out
(i+1))/2. I would then send lap time to base station (laptop or PDA
with WI-Fi or Zigbee card...)

In ascii:

*
Athlete * *
-------> --------T(in)-------------T(out)----------->
Path * *

* *

* R *
F
* *

* *

* *

* *
*
RF Source is off track. T = RF Power Threshold * = RF power.

This is an idea I've been toying with in my head. Anybody else have
suggestions?

Many thanks, LB
Temporily in Chicago, IL

Hi LB,
Two possibilities. RF - you have a small base station with a highly
directional antenna to define your 'finish' line. If you mount it on a
pole or a wall, and aim it down, you can get pretty well defined pattern
for limiting your trigger point. Biggest problem will be bounce to the
far side of the track, and getting double triggers. Your individual
runners then have a small package with received, microcontroller,
perhaps a small LCD display for times, and even a small speaker so it
will beep as they pass the finish line.

Second possibility - IR LEDS. Give you a nice, well defined field, esp.
if you raise it up and have it look down so the bounce will be up in the
air on the other side of the track. Give it modulation, perhaps a
time code, so it is easier to pick out the signal from any noise. Then
you just have a photo-transistor as your reciever, as well as the same
LCD, micro, speaker, etc.

Charlie
Edmondson Engineering
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