Using RF for lap timing?

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Hey guys. I have been trying to build a lap timing device that times my laptimes around a track with my bike. i have built something that trips with a laser but only one person can ride then. What I want to do is build a device that can time multiple bikes at the same time. 

 

Is it possible to use radio transmitter and receiver devices such as the nrf24L01 or the 433MHz units to act as timing devices?

 

I have thought about this and as far as i can understand you will be able to transmit unique ID's for each different bike if they all fitted with a transmitter. However the part that i am not sure about (not even sure if it is possible) is how do u ensure the unique ID is sent at the exact same spot each lap? Like when the bike gets closer to the receiver the receiver will pickup the unique ID and do its thing and display the time but how can i make sure it picks up the unique ID at the exact same place every time?

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There's no such thing as 'exact'. You need to define what is acceptable. For F1 cars i think they time down to the millisecond, so your application would be somewhat more. When i race, i get a transponder for timing. I have wondered how these work. I'd guess they would use a spread spectrum technique to send a ping when they get polled by the finish line loop. Each transponder has a unique number which is used to seed the LFSR (Google that). Reception is somewhat trickier as you need a number of correlators to extract multiple responses.
Gps uses such a technique to allow a number of transmitters on the same frequency to send data at the sane time.
I've given you a number of keywords that you can Google. In short, this is not a trivial task and you'd probably want an engineering degree. The hardware would be relatively simple, but the software is where the fun is. The receiver would probably use a DSP.

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<edited inappropriate response...sorry>

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

Last Edited: Mon. Feb 22, 2016 - 03:18 PM
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calvingloster wrote:
What I want to do is build a device that can time multiple bikes at the same time.

 

You might want to explore "chip timing" as is used in running races.  AFAIK those are RFID.

 

 

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Kartman wrote:
There's no such thing as 'exact'. You need to define what is acceptable. For F1 cars i think they time down to the millisecond, so your application would be somewhat more. When i race, i get a transponder for timing. I have wondered how these work. I'd guess they would use a spread spectrum technique to send a ping when they get polled by the finish line loop. Each transponder has a unique number which is used to seed the LFSR (Google that). Reception is somewhat trickier as you need a number of correlators to extract multiple responses. Gps uses such a technique to allow a number of transmitters on the same frequency to send data at the sane time. I've given you a number of keywords that you can Google. In short, this is not a trivial task and you'd probably want an engineering degree. The hardware would be relatively simple, but the software is where the fun is. The receiver would probably use a DSP.

 

Thanks Kartman, u have created an endless thought process in my head now and my thoughts are seeded by the things i read which in turn makes me read more and so on until i become unseeded and can no longer generate different thoughts to read more and feed my though process..........

 

Ok i was thinking something in the line of covering the receiver with impenetrable signal material and only allowing signal in from one angle haha. Im just joking but never thought it would be so complex. thank you for giving me all those keywords to google. what i have gathered from it is that i will need to generate checksums to quantify how good (close) the signal is from the receiver it identify when its good enough to actually say ok start and stop timing. This is however a few light years away from my grasp. i will continue reading however.

 

 

I was thinking, how about a laser trip beam that signals the receiver to only start listening when the laser is tripped? what do you guys think about this? so the transmitter will continuously be transmitting a unique ID and once the laser trips it listens for a few milliseconds for a unique ID? 

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How do you determine who has broken the beam? How do you distinguish between multiple transmitters?
The current systems have a big loop at the finish line. This signal magnetically couples (like a big transformer) to the transponder. Since the field doesn't go far beyond the loop, that ensures you trigger only transponders in the loop. Then you're left with the challenge of discriminating between multiple transponders.