A really simple Infrared checker.
For this project all you need is an Infrared phototransistor, a 330 Ohm resistor, a LED and a 9 Volt battery. Connect the positive pole of the 9 Volt battery, to the LED's cathode and then, the anode to the 330 Ohm resistor. Afterwards, connect the resistor to phototransistor's anode and the cathode to the positive pole. Solder everything on a perfboard following the schematics or the various pictures, related to this project.