PIC microcontroller controlled remote anti-theft alarm circuit

The circuit of AG9900 intelligent remote control motorcycle anti-theft system is shown in Figure 1 and Figure 2. The single chip microcomputer PIC16C54 is the main controller, and VD5026 and VD5027 are the codec circuits. The alarm has the functions of three-level interlocking anti-theft with sound and light, flashing rolling alarm, anti-robbery, keyless driving, overtaking and searching for cars, releasing the flameout and sensitivity adjustment. Its full remote control operation is very suitable for installation and use on motor vehicles.

1. Transmitter circuit

The VD5026 and T4 in Figure 1 form a remote control transmitter unit. One 12V power supply directly supplies the high-frequency transmitter circuit, and the other one is divided by D10, R24~R27 to obtain a voltage of about 5V when the transmitter keys K1~K4 are pressed, and then supplied to the VD5026 through D6~D9. When one of the transmitter keys K1~K2 is pressed, the pin will output a coded pulse string, which is transmitted after being modulated by T4 at high frequency (the frequency of the high-frequency oscillator composed of T4 is about 180MHz). A0~A7 of the VD5026 are the encrypted address coding input terminals, and each bit has three states: "1", "0", and open circuit. A8~A11 (D0~D3) has a dual input function, which can be used as the address coding input terminal together with A0~A7, or as the control data coding input terminal, respectively connected to "0" or "1" (not marked in Figure 1). Pin TE is the start terminal for sending the coding pulse, and the low level is effective. When the encoding pulse of the transmitting end pin of VD5026 is at low level, it outputs the serial pulse of the encrypted address and data encoding. The oscillation resistor R28 is connected across the pin, and its frequency f0 = 1.6 × 106 / RH, which is about 900 Hz.

2. Receiving, decoding, instruction processing and interface circuit

Figure 2 is the receiving, decoding and output circuit. When antenna Y receives a high-frequency signal, it is input to the common emitter-common base cascade high-frequency amplifier composed of T1 and T2 through high-pass filtering by C1, L1, and C3, and then input to the emitter of T3 through C4. T3 and the external LC network form a super-regenerative detection circuit, which detects the 900Hz coded pulse string, which is amplified by IC4 in two stages and sent to the ***VD5027 pin (coded pulse input terminal). When in use, the encrypted address code of VD5027 is required to be consistent with the code of VD5026. Its ~ pin (D0~D3) is the control data output terminal, and each bit has only two states of "1" or "0". The ~ pin is the decoding output terminal. When decoding is effective, VT changes from low level to high level. This pin and ~ pin together provide the basis for state judgment for the single-chip microcomputer.

The single-chip microcomputer receives the decoded signal and puts the system into the corresponding working state. Its , ...

The 2P plug of this unit supplies power to the electronic horn of the alarm.

The sensitivity of this machine is adjusted by controlling the level of the BZ vibration signal output to IC2 pin (a total of 10 levels, not shown in the figure). Due to space limitations, other functions of this machine will not be described in detail here.