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

The automatic alarm includes DTMF automatic dialing circuit, password control circuit, voice detection and alarm circuit , telephone interface circuit, power supply
circuit and keyboard display circuit.
    (1) The MT8888 chip in the automatic dialing alarm part not only has the function of sending and receiving DTMF signals, but also has the function of detecting telephone signal tones
. It can be easily interfaced with the MCS51 series microcontroller. In this system, MT8 and peripheral circuits are shown in Figure 13-41. Its receiving
part adopts single-ended input and consists of Rz0 1, R2U2 and C20i. Its sending part Rs, R206, G, Ck and XTAL2 It
is composed of R2c3 and Goi. Since the IRQ and CP terminals are open source outputs, pull-up resistor R204 is required. C203 is a decoupling capacitor. DTMF
IN and DTMF OUT are connected to the telephone interface circuit.