Fireproof and anti-theft telephone intelligent alarm circuit-voice circuit

The voice integrated circuit ISD1420 is a single-chip solid-state voice integrated circuit. Once the voice is recorded, it can be stored for more than 10 years and can be recorded repeatedly
100,000 times. The recording and playback time can reach
20 seconds. When the REC button is pressed, recording starts
and data is stored from address 0 until
the memory is full and the button is released.
When the PLAY button is pressed, playback starts
until the PLAY button is released or the memory
runs out. The voice circuit of this system is shown in
Figure 13-42. The voice signal is picked up by the electret microphone and input to the amplifier inside the chip
from both ends of MIC and rvnc REF for amplification. The amplified audio signal is output from both ends of sp+ and sp- and drives the speaker to produce sound. In this circuit, SP+ is used to connect to the telephone interface circuit to get voice signals in and out. C305 and R305 are gain adjustment circuits.