Keypad matrix expansion method

Details Keypad matrix expansion method Keypad matrix expansion method

H - Electricity

01

H

H01H 13/70 (2006.01) H03M 11/20 (2006.01)

Patent

CA 2335405

A keyboard matrix circuit includes means defining a first junction location and a second junction location. Two switches are wired in parallel between the junction locations, each switch being in series with a diode, and the two diodes being oppositely directed. Each junction location connects to line voltage along a current path which includes a resistance, so that current flow from line voltage to the respective junction location will cause that junction location to have a voltage lower than line voltage. For each junction location there is defined a current path permitting current to flow away from the respective junction location. Also, for each junction location current path there is provided a control means which either allows or disallows current flow along the respective location current path. Monitoring means, preferably in the form of gates, are.provided for detecting the voltage level at the respective junction location, thus providing a reading from which can be determined the open/closed status of the respective switch.

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