Interface circuit between MT8880, AT89C51 and voice circuit

Interface circuit between MT8880, AT89C51 and voice circuit

There are five registers inside the MT8880, which are the receive data register, the transmit data register, the transceiver control registers CRA and CRB, and the transceiver status register. In this design, since only the sending data register, sending and receiving control registers CRA and CRB are used to send DTMF signals to realize the automatic dialing function, only these three registers are introduced here. The data in the send data register determines the frequency of the dual audio signal to be sent, so data can only be written to the send data register. The two transceiver control registers occupy the same address, so whether to operate CRB is determined according to the value of the register selection bit in CRA. Its interface circuit is shown in Figure 4.

The ISD1420 voice chip uses direct analog storage technology, and has excellent recording and playback sound quality, and has a certain reverberation effect; its peripheral components are simple, and only simple resistors and containers can be used to form a simple recording and playback circuit; no backup is required Power supply, long information storage time, no special programmer or voice developer required; strong address selection capability, the memory can be divided into 160 segments for management, resulting in a minimum recording and playback time of 125ms. The interface circuit diagram is shown in Figure 4.

Voice segmentation method: The address input terminals A0~A7 are arranged from low to high. Each address represents 125ms addressing. 160 addresses cover the voice range of 20s (160×0.125s=20s). The recording and playback functions are from Starting from the set starting address, the end of recording is determined by the stop operation. The chip automatically inserts an end mark (EOM) at the end of the segment; and when playing back, it automatically stops playing when it encounters the EOM mark. In this design, because four segments of alarm prompt voice are needed, each voice segment is set to 5s during the design, and its starting addresses are 00000000B, 00101000B, 01010000B, and 01111000B. It can be seen from these four starting addresses A7, A2, A1 and A0 are all 0, so connect them to ground.