This is the simple circuit of proximity infrared detector, proximity sensor based infrared. The applications of this circuit are the most varied. From placing it in the front door to prevent people stop in front of this circuit, or even placing it in the back and front of the car to warn other drivers when they get too close to the park.
The circuit operation is based on emitting a burst of infrared light signals which bounce off the close object is received by another component. When received the system detects proximity with the LED output is activated (shines).
The integrated circuit is a generator / decoder tones that well meets the needs of this design. Both the photodiode and phototransistor be situated with units suitable approach to improve the range. With simple LED reflectors are available scope of the order of meters. With convex lens can cover distances of five meters. It is convenient to sacrifice some range but placing UV filters and SUNLIGHT which do not let the phototransistor (receiver element) sunlight.
The power of this circuit can be any voltage between 5 and 9 volts.
To drive external circuitry will suffice to replace the LED by an optocoupler, which actuated by means of its internal transistor circuit to be controlled.