Extension Phone Ringer

Posted on Dec 29, 2012

The ac ringing voltage (typically 40 to 90 V at 26 Hz) is rectified by U1, the tone-ringer IC, and is used to drive

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that IC"s internal tone-generator circuitry. The tone-generator IC includes a relaxation oscillator (with a base frequency of 500,1000, or 2 000 Hz) and frequency dividers that produce the high- and low-frequency tones, as well as the tone-warble frequency. An on-board amplifier feeds a 20-Vpp signal to the transducer.

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