straight RF with 433.92MHz modules must be encoded if you don't want to have false trigger at the receive end
like MM53200/UM3750/MC145026 etc but the modulation speed for these modules is limited to 2/4KHz and the code/decode over 10/13 bits + 3 iteration is very long 
Genesis92:
straight RF with 433.92MHz modules must be encoded if you don't want to have false trigger at the receive end
like MM53200/UM3750/MC145026 etc but the modulation speed for these modules is limited to 2/4KHz and the code/decode over 10/13 bits + 3 iteration is very long
But "Very" is a relative term. In terms of human performance in a race it's not Very at all, it's instant.
ok so some number application
1/4000 = 250us per bit
13 bits = 3.25ms
3 iterations = 9.75ms
so in the best case 10mS only for the receiver side (neglecting the speed of the EM wave xD)
But upon reception of the VERY FIRST bit, the reciever can start the counter. The rest of the signal is simply confirmation. There's 99% of your latency GONE!
no because it's internal to the chip and the "receive decode" signal goes low only when the 3 iterations are ok. and it's 66% not 99% because you need at least one complete message decoded.
except if you do the OOK mod/demod or balanced manchester by the arduino board.
but the emitter speed is allways 4KHz max
Now i belive that if i just use a 100m cable (cat5 for instance?), it will not works due to the length...
I believe a wired solution could work quite well.
A basic sensor signal, even at 10kHz (100µs timing resolution), should transmit reliably. Some simple signal conditioning might be required at the Arduino end. Enough wires for both power and sensor output.
Hi, looking back on it all, a piece of twin flex to 100m, that just has a on or off state is going to be fine when you consider the reaction time of the ultrasonic detector.
How does it detect start and stop?
Tom...... 
Woua loads of information for me to process in here!
I am not searching for extra accuracy, millisec is perfect...
So i will try the naive solution with 100m cable for the 5v sensor and see what happens
KenF:
Perhaps we should arrange a race of RF vs Cat5. By the time you allow for the capacitance of 100m of twisted pair, I think it should be a pretty even match.
If you properly match the driving impedance and the termination, the capacitance doesn't matter.
dlloyd:
I believe a wired solution could work quite well.A basic sensor signal, even at 10kHz (100µs timing resolution), should transmit reliably. Some simple signal conditioning might be required at the Arduino end. Enough wires for both power and sensor output.
Could you elaborate on the simple signal conditioning thing?
I have a similar problem than the OP's, except with shorter distances (less than 10 meters) but I really suck at electronic (I originally picked Arduino to learn it) and never worked with cables more than 20 cm long.
@LienRag, please start another topic describing what you're using (sensor part#, Arduino board) and what you're trying to achieve / problems etc. I'm sure someone here could help if I can't get around to it.
It's here:
http://forum.arduino.cc/index.php?topic=279673.0
On short term, the best solution may be to work at high temperature; but on long term, I want to put the cards and shield outside the oven, and wire them to the sensors inside (so, wire lenght ranging from 2 to 10 meters).
How to handle long wires is the same question as the OP's I think, except that I want 10 m maximum when he asks 100 m?
Start a new topic. There is no generic "how to use long wires". It depends on the sender and receiver. There is also no such thing as a generic sensor.