A sensor interface, comprising: a circuit to allow an amplitude and frequency of a sinusoidal voltage waveform to be digitally monitored, comprising: a sinusoidal-amplitude-to-digital-output, SADO, circuit , comprising: a comparator with an input terminal , a reference terminal , and an output terminal ; a digital bus connected to the output terminal; a reference voltage source connected via a resistor to the reference terminal; and a feedback resistor connected in parallel with the comparator between the output terminal and the reference terminal to provide hysteresis and convert an input voltage received at the input terminal into a digital pulse-width modulated, PWM, waveform that varies non-linearly with amplitude of the input voltage; said sensor interface further comprising: a sine wave generator , for applying a sinusoidal voltage waveform to a sensor, connected to the input terminal of the comparator to provide the input voltage as a sinusoidal voltage waveform; and a field programmable gate array, FPGA, or microprocessor device connected to the digital bus and configured to calculate the frequency of the sinusoidal voltage waveform using the PWM waveform received at the comparator output terminal, and to calculate the amplitude of the waveform by referencing, from a lookup table, an observed duty cycle of the PWM waveform .with an associated amplitude according to a duty cycle function. a comparator with an input terminal , a reference terminal , and an output terminal ; a digital bus connected to the output terminal; a reference voltage source connected via a resistor to the reference terminal; and a feedback resistor connected in parallel with the comparator between the output terminal and the reference terminal to provide hysteresis and convert an input voltage received at the input terminal into a digital pulse-width modulated, PWM, waveform that varies non-linearly with amplitude of the input voltage; said sensor interface further comprising: a sine wave generator , for applying a sinusoidal voltage waveform to a sensor, connected to the input terminal of the comparator to provide the input voltage as a sinusoidal voltage waveform; and a field programmable gate array, FPGA, or microprocessor device connected to the digital bus and configured to calculate the frequency of the sinusoidal voltage waveform using the PWM waveform received at the comparator output terminal, and to calculate the amplitude of the waveform by referencing, from a lookup table, an observed duty cycle of the PWM waveform .with an associated amplitude according to a duty cycle function. a sine wave generator , for applying a sinusoidal voltage waveform to a sensor, connected to the input terminal of the comparator to provide the input voltage as a sinusoidal voltage waveform; and a field programmable gate array, FPGA, or microprocessor device connected to the digital bus and configured to calculate the frequency of the sinusoidal voltage waveform using the PWM waveform received at the comparator output terminal, and to calculate the amplitude of the waveform by referencing, from a lookup table, an observed duty cycle of the PWM waveform .with an associated amplitude according to a duty cycle function. <EOS>