Telephone ringtone automatic adjustment circuit diagram

This figure shows the automatic ring tone adjustment circuit added to the HA18 (V II) P/TSD telephone (the dotted box is the circuit of the original telephone). As the number of ringing increases, the volume and tone of the ringing sound gradually change to achieve the purpose of ringing program control. The entire device requires no external power supply. The circuit is simple, reliable and does not affect the communication line.
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