Abstract: A method of operation of a pet door system with a controllable lock and circuitry including a resonant circuit having an antenna and an element to vary the resonant frequency of the circuit according to a setting parameter, a drive circuit for driving the resonant circuit with a drive signal, and a demodulator, the method including a setting-up operation comprising varying the setting parameter 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. The method further includes a reading operation comprising reading the first value, driving the resonant circuit at the first driving frequency with the setting parameter set to the first value, and attempting to derive data from the demodulator.

Abstract: A method of operation of a pet door system with a controllable lock and circuitry including a resonant circuit having an antenna and an element to vary the resonant frequency of the circuit according to a setting parameter, a drive circuit for driving the resonant circuit with a drive signal, and a demodulator, the method including a setting-up operation comprising varying the setting parameter 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. The method further includes a reading operation comprising reading the first value, driving the resonant circuit at the first driving frequency with the setting parameter set to the first value, and attempting to derive data from the demodulator.

Abstract: A through-flow electric water heater has a cannister through which water to be heated flows and in which are disposed a first heating means comprising a plurality of electric heating elements and second heating means comprising at least one electric heating element. A control unit comprising a microprocessor receives a first input signal from a flow sensor and a temperature sensor which sense, respectively, the flow rate and temperature of the water flowing into the cannister and switches the plurality of heating elements of the first heating means on and off in different combination to achieve different heating levels and adjusts the level of heat dissipated by burst firing the at least one heating element of the second heating means to achieve a desired total heating level.