Push-button dial for a telephone

摘要

A solid state push-button dial circuit in which a push-button key pad uses a simple on-off switch for each key to mute the receiver and open the circuit to the transmitter while a dial tone is being generated. The circuit, when operating with the speaker phone, mutes the speaker phone when the key is depressed. The phone can be easily switched to a polarity-sensitive state in which the tone generator is turned on only if the proper polarity is present on the telephone line.