infrared emittors and sensors
IR emmitter/sensor pairs are all aroud you. How about your TV remote? Or the sensor that keeps your garage door opener from closing on you? And on and on.
For experimenting any of the common opto-isolators, (look in your electronics catalog), are fine.
A basic isolator consists of a Gallium Arsenide infrared emitting diode, and a silicon phototransister mounted together in a dip pacage. The pair can be seperated whth a airgap in which case the device is called a photo-interuptor.
If you can forward bias a diode, you can operate an opto-isolater or interupter.
There are several forms of output devices used in isolaters ranging from simple transistors through darlington pairs, scrs and triacs.