Devise a system which will allow a door to be opened only wh

Devise a system which will allow a door to be opened only when the correct combination of four push-buttons is pressed, any incorrect combination sounding an alarm.

Solution

This electronic combination lock is operated by depressing the proper combination of pushbuttons mounted on the faceplate of a circular handle, then rotating the handle to open the bolt. The pushbuttons are held outwardly by radially extending spring wires within the handle that also provide electrical connection, when a pushbutton is depressed, to inclined contacts mounted to the rear of the faceplate. Electrical leads extend through a hollow shaft connected to the handle.

The bolt is restrained in the locked position by a magnetically actuated locking pin which projects into a bore in the bolt. The shaft is connected to the bolt by a spring. When the proper pushbuttons are selected, electrical circuitry disclosed herein actuates the magnet, removing the pin and permitting the bolt to be opened by handle rotation. If the wrong combination is depressed, an alarm signal is produced, the magnet is not actuated, and rotation of the handle expands the spring without moving the bolt.