The principle of operation of an infrared led and receiver: the interruption or reflection?

Good day!
The goal is to make the counter count of the people in the room using infrared LEDs and receivers to automatically turn on the light.

To determine a person has entered or left will be used 2 infrared receiver. With system everything is simple and clear. Now you need to choose how you will operate infrared receiver: interrupt (IR led is opposite the receiver when someone enters the signal will be interrupted) or through reflection (IR led and receiver are close when someone enters the signal reflected from the obstacle and get to the receiver)

Important conditions: the minimum distance between the receivers, interference, and reliability. On what principle it is better to implement the system?
September 19th 19 at 12:34
1 answer
September 19th 19 at 12:36
Solution
On interruption of the beam. The range of the IR sensors operating in the reflection does not exceed 20 cm and is strongly dependent on the object color.
The minimum distance between the beams depends on the angle of divergence of the light. Even with a simple lens (converging lens + lens hood) it is possible to spot 1 cm at a distance of a few meters.
To protect against interference, the beam must be modulated. Accordingly, in the signal receiver checks the presence of the desired frequency level.

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