The core part of the host of this scheme adopts PIC16C57 single chip microcomputer. The MCU adopts RISC structure, which separates the data line and instruction line, that is, the so-called “Harvard structure”, with high execution efficiency and fast speed. At the same time, this single-chip microcomputer instruction is mostly single byte and adopts simplified instruction set. It has the characteristics of power saving, strong load capacity (output pull current can reach 25mA), low price and so on.

 Signal input interface

The signal input interface circuit is composed of super regenerative receiving module and PT2272 decoding circuit. The super regenerative receiving module contains amplification, shaping and decoding circuits. It has four leading out terminals, namely positive power supply, input terminal, output terminal and ground. The output signal is supplied to the decoding circuit PT2272. PT2272 is a low-power, low-cost general-purpose decoding integrated circuit manufactured by CMOS process. It is paired with the coding integrated circuit PT2262. The PT2272 integrated circuit in the host adopts 8-bit address code and 4-bit data code, with a total of 6561 non repeated codes. When in use, the frequency of the transmitting part and the receiving part must be consistent and the address code of the codec IC must be the same. In addition, the oscillation resistance of the codec IC must be matched, otherwise the transmission is invalid.

Circuit design diagram of a smart home security system

 Host signal processing circuit

The host signal processing circuit is mainly composed of dual audio decoding circuit, PIC single chip microcomputer signal processing circuit, number storage circuit, polarity conversion circuit, alarm sound circuit, etc.

If the host has recorded the alarm voice information and telephone number before use, in case of an alarm, in addition to the local high-loudness alarm sound, it will start dialing the telephone number set by the user in turn after a slight delay. These functions are controlled by RC2, RC5 and RC7 in the single chip microcomputer. RB0 and rb6 ports are connected with the external 24c02eeprom memory. RB0 port is the clock control end of 24C02, rb6 is the read-write data end, and the external resistance network of RC4, RC1, Ra0, ra1, ra2 and RA3 ports is the dual tone multi frequency signal network. After receiving the call, the user first outputs the high level from the RC2 port, and the telephone number data set by the user is called out. It is output to the external line through the dual tone multi frequency resistance network to start dialing the telephone set by the user. After the user presses the answer key, the RC7 port of the single chip microcomputer outputs the low level, which changes the 24th pin of the ic51sd1110 voice integrated circuit to the low level, so that the integrated circuit is in the playback state, The recorded alarm voice information is output to the external line through the polarity conversion circuit through the SP + terminal of pin 14, and then transmitted to the user’s phone. If the first group of phone numbers are blocked, after receiving the feedback busy and hang up signal, the host will dial the second group of phone numbers and cycle back and forth.

When conducting local or remote deployment, the 14th pin of IC2 outputs high level and drives LED1 to emit light to indicate successful deployment.

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