Can you help me? I want to use infrared as an electrical circuit can feel the presence of man in space 40 to 200 m. Water is not impertont but on port rxd.
Look for PIR sensors (Passive Infra Red). Check the datasheet for what signal they give out. Interface. Write program. Use.
Not sure what you mean by "Water is not imperont [sic!]". Do you mean that the sensor need not support IP67 or similar, i.e. withstanding rain or immersion?