IR opto detector question

[Lucifre]

i am trying to design circuit controlled by Infra red LED. my question is ...
when opto detector (sensor) is illuminated by infra red light, is it the resistance that changes across its two pins? or is it something else? I've seen op amps used for this type of circuits but i am trying to design one myself from scratch.

 

[on1aag]

Hi,

When a detector gets illuminated by (infrared) light it will start conducting.
It's resistance decreases proportionally with the increase of illumination.
You could start with a continious ir source, but you will find that there are
a large number of other ir sources that will saturate your sensor, like the
sun or lighting bulbs,... Therefor you should use a pulsed ir source and a
tuned receiver to avoid these problems.

on1aag.