Handset attachment for simplex call station - uses operational amplifier and potential divider for calling and reception

摘要

The circuit is used to operate a handset at a simplex loudspeaker call station. The receiver (H) and the speaker (M) of the handset are connected in parallel by a connecting cord (c, d) to the input of a high impedance amplifier (OP). This forms part of an adaptor module (HM) which can be fitted to the telephone set (SA). A push-button (T) determines the speaking direction. The speaker signal is amplified by the operational amplifier and passes through the transformer (UE) to the loudspeaker system. The receiver signal at the transformer is attenuated by the potential divider (R1, R4) to a level low enough not to overdrive the handset receiver. The module also has a cradle for holding the handset (HA).