answering machine circuit

The answering machine circuit is shown in Figure l-55c Ffr.
(1) When recording, close switch S4 and YYH40 enters the work preparation state. After pressing the button switch S2, the circuit starts recording.
The speech signal generated by microphone B is amplified by the amplifier composed of Ala and then enters the AU1 end of A2 for speech processing. It is converted into a digital quantity and then
stored in DRAM. During the recording period, the PR terminal is high level and LED1 does not light up. After the recording is completed, the PR terminal is low level. LED1 glows.
Switch S4 is turned off and recording ends.
    (2) When playing the sound, you must first close the switch 'S4, and then press the button switch S1 to start the sound playback. The speech signal is output from the AUO terminal,
amplified by Alb, filtered by a filter composed of Alc and resistor-capacitor components, and then enters the LM386. Perform power amplification to drive the speaker to produce sound. Circuit -board
composed of YYH40 chip