LED's pulsed for say 200% of their 'normal' current at a 50% duty cycle appear brighter than 100% current for 100% duty cycle even though the maths says that it's all the same average current. Remote controls are almost always pulsed. In fact, if you want to get more than a couple of feet covered, you almost *have* to pulse the ir LEDs. Note that since current in a series circuit is the same through all the series elements (non-reactive), you can string several LEDs in series and pulse the whole string using the same amount of total energy that you would have used to pulse just one. Instead of wasting the energy as heat in a resistor, you recover it as more usefil light from the LEDs. Multiple LEDs give you better 'coverage' than a single LED.
VCSEL laser diodes in plastic LED type packages collimated to 2 degrees beamwidth are simple to drive (constant current, no monitor diode needed), and best of all--VCSEL laser diodes begin lasing at 4 ma. ir beams can be 'hidden' on the tx and rx ends of the link by dark plastic (as your VCR has on it's front panel)-when you scrap a junk vcr, ALWAYS SAVE the black plastic in front of the ir recveiver module, same with some hand held remote control transmitters. VCSEL laser diodes are ideal for moderate range free space laser comm ap because the drivers are simple!
Microchip PIC specific ir I/O
Ubicom SX specific ir I/O
ir Remotes@ LEDs@, Light Sensors@
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<A HREF="http://piclist.com/techref/io/irs.htm?key=ir"> IRDA, 890nm, 940nm, Infra-Red Input / Output</A>
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