> 18" so IR should work.  I just did a x4 pulse width increase

Alan, IR will definitely work at 18". Things to look at

- source impedance of the power supply. If the voltage doesn't hold up
for the duration of the transmission, then power output will drop off. A
reservoir capacitor of 100uF or more can help, particularly with battery-
operated transmitters

- pulse width / limiting resistor / sharpness of the driving signal /. Most
protocols use very short pulses, which allows for high current through
the LED. Consequently the current-limiting resistor is often small, perhaps
only 1 or 2 ohms. A fast switch means more even power, without rounded
edges (which is why I tout the Zetex range)

- a sensitive and discriminating receiver

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