Patent ID: 8839556

Claim:
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.