In this application (sensing presence of an object), you'd be wise to
use an integrated IR receiver. This is a 3 pin device that will output
a logic signal when your object is present. It's exactly what's used
to receive signals from a TV remote. These devices are very common,
and very cheap. This willl eliminate all problems with ambient light.
You will need to switch your LED on and off at about 40kHz.

Neil

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