A keypad encoding circuit contains a voltage dividing network and an
integrated circuit. The voltage dividing network includes a string of
resistors that generates an encoding signal voltage. The integrated
circuit converts the encoding signal voltage into a digital value
indicative of which of the keys has been pressed. The cost of the voltage
dividing network is reduced by forming the resistors from a layer of
conductive carbon and avoiding the cost of providing discrete resistors.
Each resistor has the same resistance even where the dimensions of the
conductive carbon patches that form the resistors vary. Providing the
resistors does not involve additional manufacturing cost because the
resistors are made in the same step as are the landing pads of the
voltage dividing circuit. Manufacturing costs associated with etched
printed circuit board layers are avoided because inexpensive printed
layers are used to realize the required traces and resistors.