Password type motorcycle anti-theft device

This password-type motorcycle anti-theft device uses multiple electrical switches on the vehicle as password keys. When driving, the relevant electrical switches must be turned on in a set order within a set time before the vehicle can be started, so the anti-theft performance is good.

Working principle :

The circuit is shown in the figure. CS1 is the main power switch, CS2 is the parking switch (closed when parking, disconnected when driving), CDI is the motorcycle electronic ignition, E is the on-board 12V battery, and the rest is the password lock circuit. S1~S4 is a four-analog switch. When the car lock is opened, CS1 is connected and CS2 is disconnected. At this time, S1~S4 are all in the disconnected state because the control terminals are all low level, so the thyristor SCR is cut off, the relay does not work, and its normally closed contact J1 shorts CS2, and the engine cannot start. If you want to unlock, you need to open the point a first. The switch of the light connected to point b is turned on, S1 is turned on because the control end gets a high level and is self-locked through feedback from VD2 and R2. Then the switch of the light connected to point c is turned on, S2 is turned on and self-locked through feedback from VD4. Finally, the switch of the light connected to point c is turned on, S3 is turned on, the power supply triggers SCR through S1~S3, J is attracted, J1 is disconnected, CDI enters the ready working state, the car can be started, and J2 disconnects the power supply of the password lock circuit. Since SCR can maintain conduction without trigger voltage once it is triggered, J remains attracted from then on, and the car runs normally.

In addition to the three real password input terminals a, b, and c in the figure, there are also three pseudo code input terminals d, e, and f. During the unlocking process, if the switch of the light connected to any of the terminals d, e, and f is opened by mistake, S4 is turned on, the S1 control terminal is grounded, and S1 is disconnected. At this time, if S2 is turned on, S2 is also disconnected. At the same time, capacitor C is charged. Since the input impedance of the CMOS analog switch control terminal is very high, C has no discharge circuit, and the voltage on it keeps the S4 control terminal at a high level, S4 remains connected, and S1 remains disconnected. After that, any attempt to unlock will be invalid. C and resistor R5 also form a time-limited circuit. Once CS1 is turned on, the power supply will charge C through R5. If the lock cannot be unlocked within the limited time, the voltage on C will increase to connect S4 and disconnect S1. At this time, the circuit enters a locked state and refuses to try to unlock again.

Component selection and production :

J uses a small 12V relay, and the rest of the components are shown in the figure. When making it, put the circuit board into an insulating box, and connect the cold end lead wire of the light switch and the password input terminal with a miniature plug and socket to facilitate changing the password at any time. The entire device can be hidden under the car seat or in the headlight shell. After installation, just adjust the resistance value of R5 to make the time limit appropriate, and you can easily open the lock yourself.