Patent ID: 8866642

Claim:
An electronic keyboard, comprising: a plurality of keys arranged as a matrix of two or more rows and two or more columns, each key comprising: a plunger; and a conductive element on the bottom of said plunger said conductive element having a characteristic resistance; an electrical circuit mounted on a surface beneath said plurality of keys, comprising: a current source outputting a current, I x to a node whereby the current I x passes through a fixed resistance, R x , when no key of the keyboard is depressed and passes through a variable resistance, (R x *R I )/(R x +R I ), when any combination of keys is depressed where R I is a unique value for each combination of keys that may depressed; and an analog-to-digital convertor coupled with said electrical circuit such that a voltage in ut to the analog to digital convert is one of (I x *R x ) or (I x ·(R x *R I )/(R x +R I )), for converting the voltage input to a digital signal; and a controller coupled with said analog-to-digital convertor for determining from the digital signal generated by said analog-to-digital convertor that two keys are simultaneously pressed, and for identifying the two keys that are pressed, for any two of said plurality of keys.