Switching device actuated by a transponder

1. A switching device actuated by a transponder for the generation of a switch signal, comprising:

an oscillating circuit with a capacitance;

an identification coil; and

an oscillator amplifier;

wherein the identification coil and the capacitance determine the resonant frequency of the oscillating circuit,

a frequency observer which evaluates the frequency tuned in the oscillating circuit and which when finding a change compared with an off-load state generates a switch signal, and

wherein said device further comprising a switch which either closes the oscillating circuit or connects a function circuit to the identification circuit, said function circuit being formed by any circuit which can be activated by the switch signal.

2. A switching device according to claim 1 characterized in that the switch signal is led via a control line to the function circuit.

3. A switching device according to claim 1 characterized in that the oscillator amplifier and the frequency observer are supplied with power by an independent power source.

4. A switching device according to claim 3 characterized in that the frequency observer is separably connected to the power supply.

5. A switching device according to claim 4 characterized in that the separability is realised by means of the switch which is actuated by the function circuit.

6. A switching device according to claim 1 characterized in that the switch can be actuated by the switch signal of the frequency observer.

7. A switching device according to claim 1 characterized in that the resonant frequency of the oscillating circuit is defined by the identification coil and a capacitance which is connected to the oscillating circuit for this purpose.

8. A switching device according to claim 1 characterized in that the resonant frequency of the oscillating circuit coincides with the resonant frequency of a transponder.

9. A switching device according to claim 1 characterized in that the frequency observer contains a differentiating circuit.

10. A switching device according to claim 1 characterized in that the frequency observer is formed as to identify a change in the phase relationship of the resonance oscillation tuned in the oscillating circuit.

11. A method for switching on a function circuit, comprising utilizing a switching device according to claim 1 .

12. A method according to claim 11 , characterized in that the function circuit is supplied with power by a limited power source.

13. A system triggering a function with a function circuit which can be switched on by a switch signal characterized in that the generation of the switch signal is effected by a switching device according to claim 1 .

14. A system identifying an authorization with a transponder reading device which verifies the authorization of a user by communication and by means of a transponder characterized in that the transponder reading device is connected to a switching device according to claim 1 which switches on the transponder reading device when a transponder has been presented to it.

15. A locking system for a door characterized in that it has a switching device according to claim 1 which switches on, by communication with a transponder, a transponder reading device that verifies the authorization of a user to actuate the locking system.

16. A locking system according to claim 15 characterized in that the identification coil is disposed in a door knob.

17. A locking system according to claim 15 , characterized in that the identification coil is disposed in a hollow space, the inside surfaces towards the door knob of which are covered with a shielding.

18. A locking system according to claim 15 characterized in that the shielding is made of a material that prevents losses caused by eddy currents induced in the door knob material.