In this paper, the design of an alarm automatically dial-up circuit, it has P IC58BS microcontroller as the core, with two-Audio dial-up circuit for the MT8888 chip, the signal for the detection of LM 567 chip for recording the sound of the ISD1420 chips, Some of the subsidiary telephone interface circuits, sensors on the completion of the transmission signal processing, external dial-up, and testing telephone lines, and other functions. This system is dedicated DTMF signal chips MT8888, and the use of signal detection circuit, the lines busy for the detection, automatic dial-up than the general circuit is simple and strong stability. And low cost.
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