The voice storage and playback module uses ISD4004 from ISD. The voice device adopts multi-level direct analog storage (Chip Corder) patent technology, the sound does not need to be A / D converted and compressed, and each sample value is directly stored in the on-chip flash memory, thereby avoiding the general solid recording circuit quantization and compression Quantization noise and metallic sounds caused. The picture shows the principle circuit of voice playback. Voice input is directly connected to the differential drive input of the ISD4004 pins IN + and IN- through the microphone (MIC). The voice output terminal is amplified by LM386 and connected to the voice output terminal of the radio station. The system adopts keyed recording and playback mode. 10 different voices can be recorded through the recording key, and each recording corresponds to a key on the keyboard. According to the received voice signal, 10 keys can play different voices, which is convenient and flexible to use. 
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