Design of Laser Coded Lock Based on AT89C51

2.1 Coding Principle and Implementation

The password controller is mainly composed of an AT89C51 chip that is programmed to realize its specific functions. The main principle is that when the user enters the password through the keyboard, the microcontroller will automatically convert the processed machine code into a pulse signal that controls the power on and off. After the signal is coupled, the weak signal is amplified by a triode or an operational amplifier, so that the semiconductor laser can be driven to ensure that the laser transmitter can normally emit laser pulse signals.

Password design and signal generation principle: When the user enters a number 20 from the keyboard, the binary code written into the memory is 10 100. When programming the single-chip computer, set "0" to power off for 40 μs and set "1" to power on for 40 μs. Then, when the user transmits the switch, this group of codes is taken out as a signal to control the power supply. When programming, this process is designed to be cyclic until the user stops pressing the button, and then the transmitter converts the on-off electrical signal into a laser signal and transmits it. This avoids the disadvantages of using fixed frequency waves that are easily interfered by the outside world and have a low safety factor, and improves safety and reliability.

2.2 Design and implementation of signal reception and processing

This part mainly involves the detection of laser signals and their processing. First, the hardware uses a UDU2C photodiode as the main component for detecting laser signals. However, in order to improve its detection accuracy and detection distance, an optical concave mirror is added in front of this diode so that the divergent light emitted from a long distance can be refocused, ensuring its long-distance reception and detection. Finally, the detected signal is reshaped and amplified again to make the signal meet the requirements. Here, an AT89C2051 chip is used, and then the microcontroller is programmed to implement its specific calculation processing. When the cipher receives the shaped and amplified signal, it starts to judge. If this signal is a password setting signal, then this signal is put into the memory as memory content storage; if it is an unlocking signal, the received signal is compared with the password previously stored in the memory. When the received signal is the same as the password pre-stored in the memory, the output signal A is used to start the relay of the mechanical lock device, and then the small motor is started, thereby driving the latch to open the lock. When the compared signals are different, the output signal B is used to start the alarm circuit to sound an alarm. Considering that this combination lock may be powered off during use, a power supply and power-off protection device is added here. When the power is off, the power supply is automatically connected to the battery to ensure its normal use. When the power is low, it automatically issues a low power warning to remind the user to charge. Its basic circuit diagram is shown in Figure 2 (the power-off protection device can be used by slightly modifying Figure 2).