Patent ID: 7064682

Claim:
A method of keypad decoding employing a relaxation oscillator with a resistor/capacitor time constant comprising the steps of: disposing pushbutton key switches relative to the resistor to change a resistance value of the resistor to unique resistance on a key press; detecting an oscillation frequency of the relaxation oscillator including counting clock pulses between consecutive cycles of the relaxation oscillator, detecting when a current count differs from a prior count for more than a predetermined number of oscillation frequency count cycles, if the current count differs from the prior count for more than the predetermined number of oscillation frequency count cycles, then detecting when a variance in the current count is less than a predetermined variance threshold for more than a predetermined number of oscillation frequency count cycles, and if the variance in the current count is less than the predetermined variance threshold for more than the predetermined number of oscillation frequency count cycles, then setting the prior count to the current count; and determining a key pressed from the oscillation frequency.