Radio telephone having analog key signal output for power conservation

摘要

A radio telephone has an array of manually operable switches mounted on a respective support. A processing circuit processes signals received via said switches and said support supplies signals to said processing device over a single transmission line. The processing device is arranged to determine an analogue characteristic of a signal received from the support via said transmission line in order to determine which of said manually operable keys has been manually operated. An analogue-to-digital converter can be used to measure voltage values identifying key selection or a timer can be used to measure capacitor charging or discharging.