Abstract: A speakerphone control circuit is disclosed. The control circuit includes a first electronic switch coupled between the speakerphone microphone and a hybrid circuit coupled to the telephone line and a second electronic switch coupled between the speakerphone loudspeaker and the hybrid circuit coupled to the telephone line. A first sensing circuit for sensing the microphone signal and a second sensing circuit for sensing the received loudspeaker signal are provided. The outputs of the first and second sensing circuits are multiplexed and digitized and fed to a microprocessor controller. In response to the levels of the multiplexed signal, the microprocessor determines the state of the speakerphone from among four possible states, including a first talk state, low gain talk state, first listen state and low gain listen state.

Abstract: Polarity of transducer signals is controlled in encoding apparatus of the acoustic rod type, e.g. where key-actuated strikers impact an acoustic bar having a transducer at each end of the bar, the impact giving rise to divergent acoustic waves. The wave fronts of these acoustic waves are sensed by the transducers, the output signals of which are used to produce codes corresponding to the actuated key. By varying the shape of the bar at each point of impact, the polarity of the wave fronts can be controlled so as to distinguish the operation of adjacent strikers and thus provide correspondingly coded outputs or can be combined with elapsed time sensing systems to afford more reliable encoding even in the presence of lot-to-lot differences in the bar material's acoustic wave properties--differences aggravated by temperature changes.