IR Sensors

[BrianT]

You talk of a "motion sensor". Do you mean a human presence/absence detector or a velocity measurement system.

If you are looking for humans, the easiest is to buy two ready to go PIR (Passive Infra Red) sensors. These are $10 and up and give a saturating transistor as the output. Harder to use, but more versatile, are the $30 thermopiles from companies like Melexis (which I use). Thermopiles can measure temperature remotely while the PIR style just detect a thermal anomaly and turn on the output transistor.
The thermopile approach requires you to build a reasonably sophisticated high impedance, very low leakage op amp circuit.

Tell me more about what you are trying to do and I can explain further.

HTH
Brian

[koossa]

Hi Brian

Thank you very much for your feedback!

Yes, I am talking about human presence/absence detector.
I just need something that will be reliable and it's for outdoor purposes (for security).

Do I need 2 sensors, or will one be reliable enough?

Thx a lot!!
koossa