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Using IR receiver in open collector configuration as shown in the schematic, the maximum detection distance is about 15cm. How can I increase the maximum detection distance? Current IR setup:

enter image description here

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How can I increase the maximum detection distance?

Detection distance is increased if you use more sensitive receiver or more powerful source. However, sensitive receivers will be subjected to ambient light fluctuations, and the circuit might have false detection.

Industry has solved this problem by using modulated light, with carrier frequency of 30-56 kHz, and narrow-band receivers with high gain under automatic control loop. Here is an example from vishay.com: enter image description here

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The easiest options would be to get either a more powerful LED or a larger, more sensitive phototransistor (or a photodiode).

Harder but potentially more effective at very long range would be to add an optical system to collect light and relay it onto a detector.

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