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DTMF generators dial tone telephone circuit

2016-02-09 10:29  
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A dial tone (in British English often dialling tone) is a telephony signal used to indicate that the telephone exchange is working, has recognized an off-hook condition at the telephone, and is ready to accept a call. The tone stops when the first numeral is dialed. If no digits are forthcoming, the permanent signal procedure is invoked, often eliciting a special information tone and a Intercept message.This circuit shows theTP5700 directly interfacing to a low-voltage DTMF generator. VREGt supplies the necessary 2-V minimum bias to enable the  TP5380  to sense key closures and pull its mute output high. VREGt then switches to a 3-V regulated output to sustain the tone dialer during tone generation. The TP5700 DTMF input incorporates the necessary load resistor to V-and provides gain, plus AGC action, to compensate for loop length.A muted tone level is heard in the receiver. For DTMF generators with a higher output level than the TP5380, a resistive potentiometer should be added to reduce the level at the speech circuit DTMF input.A DTMF generator refers to any electronic device capable of generating dual tone multi-frequency (DTMF) signals used for dialing touch-tone telephones.Dual-tone multi-frequency signaling (DTMF) is used for telecommunication signaling over analog telephone lines in the voice-frequency band between telephone handsets and other communications devices and the switching center.