We all know that proximity sensors are used every where including in the mobile phone covers. I teach science experiments to children but they want to learn about building simple IR proximity sensors. If you have a circuit - simple circuit - with diagram, component list and step by step instructions on how to build such a working sensor, I will greatly appreciate it. Ready made sensors are available for less than Rs. 100 ($1.5) in the market. The fun is in making them. Kids will love the experience and would be encouraged to learn and apply more knowledge in the field of electronics.
Thank you for your help.

 

Just Google 'IR sensor circuit' and check out the Images for IR sensor display, shows many examples as only 4 or 5 components are needed!
Max.

 

Thanks Max... will do...

 

An ir emitter (LED) will have a cone angle of illumination. A phototransistor or photo diode will also have a detection angle (cone). If the two are placed next to each other (slightly tilted towards each other), then the phototransistor will pick up more and more reflected IR energy as a reflective surface approaches. This is only working well in the range of 1" to about 12". You may get lucky and get a bit more range if ther are no other ir sources in the area. You can also extend the range if you use a pulsing technique (like a TV remote). That way, you are looking for differences (AC component) instead of absolute IR and you can subtract the background (DC) with a capacitor. 38khz modules exist that pulse and filter for you. Mostly made by Sharp.