Homemade motorcycle anti-theft alarm

This article introduces a motorcycle anti-theft alarm. It uses coded radio transmission and radio receiving decoding. Its features are: (1) Small size, the transmitter part can be concealed in the motorcycle body. The receiver can be carried by the driver; (2) Moderate cost (about 50 yuan); (3) No matter what means the thief uses to open the front lock, the alarm circuit will immediately emit a coded radio signal. At the same time, the engine ignition power is cut off, making the motorcycle unable to start; (4) If the thief attempts to lift the locked motorcycle onto other vehicles and transport it away, the motorcycle will also emit a coded alarm signal when it shakes; (5) Multiple motorcycles are equipped with this circuit without causing mutual interference, which is suitable for mass production by manufacturers; (6) The monitoring alarm distance is not less than 100 meters (if the distance is too far, it is difficult to catch up with the stolen motorcycle).

1. Circuit Working Principle

The circuit of the coded radio signal transmitter of the alarm is shown in Figure 1. Relay K and unidirectional thyristor VS form a switch circuit. It is used to control the power supply of the coded transmitter circuit. Al (VD5026) is a coding integrated circuit. According to different address codes and data code arrangements (grounded, positive or suspended), it can generate up to 260,000 different control signals. A2 (F03) is a miniature radio transmitter integrated module. Figure 2 is its appearance diagram. The operating frequency of wireless transmission is 320MHz, the operating voltage is 6~12V, and the operating current is 10~15mA. Transmission distance: 100 meters without antenna (the transmission distance can reach 200 meters after connecting a 10cm soft wire). Pin ① of A2 is the modulation signal input terminal; pin ② is the positive pole of the power supply; pin ⑧ is the negative pole of the power supply.

Figure 1 is in the waiting alarm state. As long as the power switch S1 is turned on and S3 is turned off (i.e. the front lock is locked), the relay J is in the released state. The coding transmitter circuit does not work, so no power is consumed.

When the front lock is opened (i.e. S3 is turned on), VS is triggered to conduct, and relay J is energized. Its contact K-1 is closed, connecting the power supply of the coded signal transmitter circuit. Al and A2 are both powered on. The 6th pin of A1 outputs a serial pulse representing the address code of the alarm, which is sent to the 1st pin of A2 through RP2. After being modulated and amplified by F03, the wireless coded alarm signal modulated by the serial pulse is radiated into the air at a radio frequency of 320MHz. As long as S3 is turned on, the normally open contact of K-2 is closed, and S3 is self-locked. At this time, even if S3 is cut off (i.e. the front lock is locked), the power supply is still in the on state. The coded radio signal continues to be transmitted. At this time, only by disconnecting S1 can the transmission of the coded radio signal be stopped.

When relay K is activated, its normally closed contact K-2 is disconnected, cutting off the engine ignition circuit, making the motorcycle unable to start. S2 (TV-1) is an all-round high-sensitivity vibration sensor. It keeps the circuit disconnected when static. When a vibration occurs in any direction, S2 is turned on once, the vibration stops, and S2 is disconnected immediately. Its working process is the same as S3 and will not be repeated.

Figure 3 is the radio decoding alarm receiver circuit. A3 (J03) is a radio receiving demodulation integrated module paired with A2 (F03) in the transmitter circuit. Figure 4 is its appearance diagram. The operating frequency of both the transmitter and the receiver is the same, the operating voltage is 3V, and the static operating current is 0.2mA. The low power consumption and high-quality resin packaging of Figure 4 enable it to be in a stable receiving state for a long time. J03 also has extremely high receiving sensitivity. It can output a square wave digital signal of about 50mV without an external antenna and has a signal-to-noise ratio of 10dB. Pin 1 of J03 is the demodulation signal output terminal, pin 2 is the positive pole of the power supply; pin 3 is the negative pole of the power supply. A4 (CD4069) is a shaping amplifier circuit that can output a 3V square wave signal. A5 (VD5027) is a decoding integrated circuit, and its address code is exactly the same as the address code in the transmitter. Because the encoding and decoding circuit can combine 260,000 different passwords, it can provide 260,000 motorcycle anti-theft devices with different signal encodings to achieve non-interference. A6 (VT665) is a music chip, where pins ① and ② are signal output terminals; pin ③ is the negative pole of the power supply; pin ④ (the top heat sink) is the positive pole of the power supply; the working voltage is 1.5~3.5V; the static current is less than 1μA; the output current is greater than 12mA. Each time the power is turned on and triggered, the stored music will be played once, and it will automatically stop working after playing a song, and the circuit will enter static state.

When the power switch S is closed, the circuit is powered. When A3 does not receive the radio coded signal sent by the transmitter, its pin ① has no signal output, A4, A5, and A6 do not work, and the entire circuit is in standby mode. Once A3 receives the radio coded signal sent by the transmitter, after its internal high-frequency amplification and shaping processing, its pin ① outputs a 50mV negative pulse square wave signal, and this signal is then amplified and shaped by the non-gate 1 to gate 3 to output a 3V positive pulse square wave signal. It is added to A5 through R6 for decoding. When the address code is determined to be exactly the same after three detections inside A5, the pin (17) outputs a high potential. At this time, V is turned on, connecting the working power supply of A6, and its pins ① and ② output audio signals to drive the speaker BL to emit a loud music alarm sound. Remind you that the motorcycle may be stolen or someone is shaking it. At this time, you should immediately go to the motorcycle parking place to check to prevent the motorcycle from being stolen. The music alarm sound is emitted along with the coded signal radiated by the transmitter. Therefore, when the transmitter stops transmitting the coded signal, the alarm sound also stops. Then transmit and then alarm, thus completing the anti-theft task of the motorcycle.

2. Component selection and debugging

The transmitter power supply G1 of this alarm circuit is powered by the battery on the motorcycle. It can be 6V or 12V. When the power supply voltage is 6V, the relay J should be 6V, and the contact current should be ≥1A. If the power supply voltage is 12V, a 12V DC relay should be selected. VS uses a 1A/50V unidirectional thyristor. S2 is a TV-1 type vibration sensor. G2 is two 1.5V No. 5 dry batteries. The models and parameters of the other components are marked in the figure, and you can select them according to the specifications.