The optical key works as an infrared door opener for house, garage and the likes. Diagram 27.0 functions as the key. It is a transmitter module which sends out a modulated
infrared (IR) beam. The modulating frequency can be adjusted through P1.
Diagram 27.1 is the actual lock (receiver module). It uses a phototransistor to receive the IR beam coming from the key transmitter module. It compares the modulation
frequency of the transmitter beam to its internal frequency. When the two frequencies match, the relay is activated, thereby opening whatever elecric door lock is connected to it.
The circuit can be modified to switch a car alarm on or off by replacing the relay with a toggle flip-flop circuit.
Parts Placement Layout
Electronic Circuits volume 1.0 - Circuit Nr. 27
The complete data of the electronic circuit described above can be found in the following book and is available from Amazon.com.
Click on the image to view the book.