Here is an electronic watchdog for your house that sounds to inform you that someone is at the door. The circuit comprises a transmitter unit and a receiver unit which are mounted face-to-face on the opposing pillars of the gate so that the IR beam is interrupted when someone is standing on the gate or passing there through. The transmitter circuit (see FIG. 1) is constructed around timer NE555 (IC1), which is wired as an astable multi-vibrator producing a frequency of approximately 38 kHz. The infrared (IR) beam is transmitted through the IR LED1.
Electronic watchdog is used for your home that sounds to inform you that someone is at the door or pass through it. The circuit comprises a transmitter unit and receiver units which are mounted face-to-face on the opposing pillars of the door or door such that the IR beam transmitted through the IR LED1 of the transmitter is interrupted when someone is standing at the door Or passing through.