I'm looking for a transmitter/receiver that will trip my lap timer button on a stopwatch. It will need to be directional so it triggers at the same point each time. I'm out my depth with RF so help would be appreciated. This is for motorcycle racing so there could be the option of another bike screening the signal.

 

I don't think this will be accurate with an RF system as there are may factors that will affect range and signal path. What about using a helmet mounted infra-red beacon (no bigger than a postage stamp) and an elevated detector so that the beacon always has a clear line of site?

When I say beacon, I mean a few high-power infra-red leds driven at around 38 - 40kHz which would match up nicely with one of the many IR receiver/ demodulators available out there.

 

When I say beacon, I mean a few high-power infra-red leds driven at around 38 - 40kHz which would match up nicely with one of the many IR receiver/ demodulators available out there.[/quote]

The IR sounds great. The stamp could be on the bike as we don't want any wires around the helmet on a racetrack.

Any suggestions on the IR receiver ? I presume that I would use a modulated signal and decoder so as to not get mixed up with the Sun's IR.

Thanks Wallace

 

As an example, something like this http://home.planet.nl/~midde639/specs/sfh506.pdf but there are others that do the same thing. They're available for various frequencies.
The transmitter leds can be driven of the good old 555 timer chip and if mounted on the bike you can have plenty of them.

You could use several receivers connected in parallel for better coverage or maybe use a lens to improve efficiency. This is one of those things that will need a bit of experimentation to get right but it seems like it could work.