How does the Basic Infrared Emitter Detector Basic Circuit work?

[Arkboy]

I searched the site but I couldn't find a topic on this.  How does the Infrared Emitter Detector Basic Circuit actually work? 
http://www.societyofrobots.com/schematics_infraredemitdet.shtml


I see the voltage going through the IR emitter and I see the voltage go through a resister then either out the Vout or the IR detector to ground.  If the detector does not see anything does its resistance go to infinity and the voltage go towards the Vout and if it does see IR its resistance drops and allows more current to flow through it and less through Vout?  Or am I missing something that would explain it?
 

[pterrus]

If there's no light detected, T1 acts like an open circuit and Vout goes to Vcc.

If there is light detected then Vout is pulled down to GND.

That's the theory anyway.  Make sure your detector is actually a phototransistor, not a photodiode, or you'll need a different circuit.

[Soeren]

Hi,

I searched the site but I couldn't find a topic on this.

Strange, it's one of the circuits I have explained lots of time.

I see the voltage going through the IR emitter and I see the voltage go through a resister then either out the Vout or the IR detector to ground.  If the detector does not see anything does its resistance go to infinity and the voltage go towards the Vout and if it does see IR its resistance drops and allows more current to flow through it and less through Vout?  Or am I missing something that would explain it?
 

Nope, sounds like you've got it

[Arkboy]

Strange, it's one of the circuits I have explained lots of time.

I must of been searching for the wrong keywords.  I saw a lot of post for the amplified circuit with people troubleshooting but I didn't see any with the basic circuit and function. Thank you for the response and confirmation though.