Switching System Having Coded Push-buttons

Abstract

An elective lock in the form of a set of pushbuttons which each have an alternately closing and opening contact. The contacts are connected in parallel with one another, so that switching off the lock is possible only by pushing solely the same buttons as are pushed in locking the device.

Description

The invention relates to a switching system for rendering an apparatus operative or inoperative. The system comprises a plurality of operating members which return to their rest positions. Several of the members are to be operated according to a predetermined code to enable the apparatus to be switched off. Such switching systems may be used, for example, for switching off an alarm apparatus, for opening a door, and so on. It is an object of the invention to provide a simple and cheap arrangement in which the code may readily be changed.

According to the invention the same operating members may be used for setting the code thereby rendering the locking on other apparatus operative and on the other hand for rendering the locking on other apparatus inoperative. A very simple embodiment of this principle is characterized in that the operating members each operate a switching member having a bistable alternately closing and opening contact, the contacts of all the members being connected in parallel in the switch-on and switch-off circuit of the apparatus.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 is a block schematic diagram of a system according to the invention, and

FIG. 2 shows schematically a part of this system.

The arrangement shown in FIG. 1 comprises a number of pushbuttons 1 which serve as operating members and are always returned to their illustrated rest positions by a spring (not shown). When a pushbutton 1 is depressed (in the direction indicated by the arrow) an associated switching member 3 is operated, for example by means of an operating slide 5 with which it is provided thereby closing a contact 7. The switching member 3 is such that after each operation the contact 7 alternately opens and closes (push-push switch) and may, for example, be of the type having two automatically alternating positions, as frequently used for switching table lamps, floor lamps and the like on and off. However, the pushbutton 1 may also be directly used for operating an auxiliary contact to control a flipflop circuit which may alternately render a transistor conductive and non-conductive. In this case the transistor serves as an electronic switch playing the part of the contact 7.

As FIG. 1 shows, the contacts 7 are connected in parallel in the switch-on and switch-off circuit, i.e. in the circuit for rendering operative and inoperative an apparatus 9, in particular a burglar alarm apparatus. For rendering such an apparatus operative an arbitrary number of pushbuttons are depressed in an arbitrary combination, for examples the first, third and fifth buttons. To render the apparatus inoperative the same buttons must again be pushed, because otherwise the said circuit remains closed. If an attempt should be made to render the alarm apparatus inoperative by depressing all the buttons, the three previously closed contacts 7 would, it is true, be opened, but the remaining contacts would be closed. Thus, the code which must be known in order to enable the apparatus to be switched off may readily be changed, since the same operating members are used for setting the code -- and at the same time switching the apparatus on -- and for switching it off, that is, the same members are used for encoding and for decoding.

An inexpensive embodiment of the switching system described having simple mechanically operated switches which each have two automatically alternating positions is also highly suited for use with burglar alarm apparatus, for example alarm apparatus of the type which is provided with an ultrasonic transmitter and receiver. This type of alarm apparatus responds after a short delay time to frequency variations of the ultrasonic signal received after reflection by sounding an alarm. These frequency variations are due to the Doppler effect. The delay time is necessary to enable the user to switch off the apparatus before the alarm is sounded. The housing 11 of the burglar alarm apparatus preferably also accommodates the pushbuttons 1. If suitable switching members are used, this time is too short to permit an intruder to find the code in time by a trial-and-error method.

FIG. 2 shows schematically a switching member which may be used in the switching system described. To a pushbutton 1 capable of being depressed against the action of a spring 13 there is secured a resilient tongue 15 which plays the part of the operating slide 5 of FIG. 1 and stepwise drives a ratchet wheel 17 made of an insulating material. The ratchet wheel carries a plurality of strip-shaped contacts 19 which in the manner shown so cooperate with two fixed contact springs 21 that the electric contact between these springs -- corresponding to the spring 7-- is alternately closed and opened at each step.

Claims

What is claimed is:

1. A switching apparatus for selectively forming a conductive path and a non-conductive whereby an associated device may be selectively energized and disabled, comprising a plurality of bistable switching members; each member comprising a manually operated button biased to return to a single mutual position after release of manual pressure, and a bistable switch having at least two contacts alternately forming a conductive and a non-conducting path in response to manual operation of the button; and means for connecting all of the bistable switch contacts in parallel with the associated device, whereby a first manual operation of selected switching members to a stable conducting state forms a conducting path across the associated device, the conducting path being removable only by manual operation of solely those members selected during the first manual operation.

2. Switching system as claimed in claim 1, characterized in that the manually operated buttons are pushbuttons which each operate a switch having two automatically alternating positions.

3. Switching system as claimed in claim 1, characterized in that the associated device it serves to switch on and switch off is a burglar alarm apparatus with a given time delay.