Best Infrared beam emitter and sensor?

[Liamlambchop]

Hey guys,

I am looking to buy a IR beam emitter (is this known as an IR LED?) and a photodiode sensor to go with it.
I am going to be using them outside and they will be used for a people counting device. The setup will be thus:
When people walk through the beam, IR radiation to the photodiode is momentarily stopped, and an arduino, which is connected to the photodiode, will recognise this as a count. The arduino will then output that data to a GSM modem, which will send the info to a webpage server.
What IR beam emitter and photodiode do you recommend I buy? I've noticed that there are a whole lot of IR LEDs which emit IR at a whole lot of different wavelengths, and likewise for photodiodes and receiving the IR. How do I know what wavelength I should buy? I need something that'll be very durable, because it'll be used outside in rain, hail, and shine.

Thanks!!

 

[duke37]

I doubt if the wavelength is important, just get a matching pair.

However, there will be a problem with ambient light. This can be alleviated by switching the led at high frequency and then filtering the received signal at that frequency (sychronous detection?).

Duke

 

[Liamlambchop]

Thanks Duke.
I am going to use an arduino to make the LED switch at 38KHz, and then use a 38KHz receiver to detect it.
Should work just fine.
Do you, or does anyone else, know where I could get some lens' for my transmitter and/or receiver, just in case I need the signal focused?