Pet door systems and methods of operation thereof

1. A method of operation of a pet door system comprising a pet door, a controllable lock for locking and unlocking the door, a resonant circuit having an antenna, a drive circuit for driving the resonant circuit with a drive signal at a driving frequency so that the antenna can communicate with an RFID device carried by a pet and so that the RFID device can modulate a signal in the resonant circuit to carry data, and a demodulator for demodulating the modulated signal in the resonant circuit to produce a demodulated signal and for deriving the data from the demodulated signal, the method comprising the steps of:

performing a setting-up operation comprising the steps of:

varying a value of a setting parameter, being at least one of capacitance and inductance, of the resonant circuit and so varying the resonant frequency while driving the resonant circuit at a first driving frequency,

detecting a first value of the setting parameter at which the resonant circuit is substantially in tune while the resonant circuit is driven at the first driving frequency, and

storing the first value of the setting parameter; and

subsequently performing a reading operation comprising the steps of:

reading the stored first value of the setting parameter,

driving the resonant circuit at the first driving frequency with the capacitance and/or inductance of the controllable element set to the read first value of the setting parameter, and

deriving data from the demodulator.

2. A method of claim 1 , wherein:

the setting-up operation also includes the steps of:

varying the value of the setting parameter of the controllable element while driving the resonant circuit at a second driving frequency,

detecting a second value of the setting parameter at which the resonant circuit is substantially in tune while the resonant circuit is driven at the second driving frequency, and

storing the second value of the setting parameter.

3. A method of claim 2 , wherein:

the reading operation, after a first phase of the aforementioned steps, further includes the steps, during a second phase of the reading operation, of:

reading the stored second value of the setting parameter,

driving the resonant circuit at the second driving frequency with the setting parameter of the controllable element set to the read second value of the setting parameter, and

deriving data from the demodulator.

4. A method of claim 3 , further comprising the step of:

determining, from the data derived during such a first phase of the reading operation, whether to make such a change to such a second phase of the reading operation.

5. A method of claim 3 , wherein:

the steps of deriving data during such a first phase and such a second phase of the reading operation are performed without interruption.

6. A method of claim 1 , wherein:

the reading operation is repeated automatically; and

such a setting up operation is not performed automatically between every successive pair of reading operations.

7. A method of claim 1 , wherein the method further includes the steps of:

detecting proximity of a pet to the door; and

in response to such detection, performing such a reading operation, but not such a setting-up operation.

8. A method of claim 1 , wherein:

such a setting-up operation is performed in response to powering-up of the system.

9. A method of claim 1 , wherein:

such a setting-up operation is performed at predetermined time intervals.

10. A method of claim 1 , wherein there are included the steps of

driving the resonant circuit at the first driving frequency,

deriving data from the demodulator,

detecting if the modulator is overloaded by the strength of the antenna signal, and

reducing the antenna signal strength.

11. A method of claim 1 , wherein the method further includes the steps of:

performing a registration operation in which such a reading operation is performed and at least some of the derived data is stored; and

performing such a setting-up operation in conjunction with such a registration operation.

12. A method of claim 1 , further including the step, during such a reading operation, of:

detecting the signal strength of the demodulated signal; and

adjusting the value of the setting parameter of the controllable element and/or the driving frequency in dependence upon the monitored signal strength.

13. A method of claim 12 , wherein:

the value of the setting parameter of the controllable element and/or the driving frequency is adjusted so as to maximize the detected signal strength.

14. A method of claim 12 , wherein:

the value of the setting parameter of the controllable element and/or the driving frequency is adjusted so as to reduce the detected signal strength to a predetermined value.

15. A method of claim 1 , wherein:

the resonant circuit includes:

an inductor, which forms the antenna, and a first capacitor permanently coupled into the resonant circuit,

a second capacitor, and

a switch for switchably coupling the second capacitor into the resonant circuit for a part of each cycle of the waveform of the drive signal, the switch and second capacitor forming the controllable element, and the part of each cycle being determined from the setting parameter.

16. A method of claim 1 , wherein the setting up operation is performed without reading the RFID device.