1. Line multiplexing technology
The smart monitor and the
electronic lock are placed in different places. The smart monitor supplies the power required by the electronic lock and receives the alarm information and status information sent by it. If the communication line and the power supply line are separated, it is bound to increase the number of cable cores and increase the safety hazard. In this paper, the line multiplexing technology is used, and only one two-core cable is used to realize the transmission of power supply and information.
At the sending end, the electronic lock boosts the modulated data signal through the pulse transformer T and sends it out; at the receiving end, the pulse transformer T steps down the received data signal and sends it to the demodulator to reduce the carrier signal in the transmission process. losses in . In order to reduce the mutual interference between communication and power supply, the selection of choke coil L and coupling capacitor C should be comprehensively considered.
Set the carrier frequency fo=400kHz, in order to ensure that most of the signal energy is transmitted to the receiving end, take L=33.7μHC1=0.047μF.
2. Current monitoring technology
In order to prevent the human sabotage of the communication line and the electromagnetic actuator from burning the coil due to excessive current flowing through the electromagnetic coil for some reason, this paper adopts the current monitoring technology in the design of the smart combination lock.
The current monitor adopts the current/voltage conversion chip MAX471 produced by MAXIM Company. The chip can convert the measured current I into the ground output voltage U, and has the characteristics of large measurement range, high precision, and the output voltage U is proportional to the measured current I.
The output voltage of the current monitor is sent to the A/D converter. The single-chip microcomputer reads the A/D conversion result to know the change of the current in the line, finds the abnormality in time through analysis, and issues an alarm signal.
3. Data communication and preprocessing technology
The intelligent monitor receives the status information sent by the lock (including the opening and closing of the lock, the first password is wrong, the second password is wrong, the third password is wrong, etc.), the current value flowing through the electromagnetic actuator coil, and the Read the power supply current value of the communication line at this moment, and combine the three to form a data block, in which the operation state occupies 1 byte, the power supply current occupies 2 bytes, and the coil current occupies 2 bytes.
During the process of communication with the electronic lock, the intelligent monitor is always in the receiving state. In order to improve the reliability of communication, this paper adopts the method of repeated transmission in the communication protocol. The electronic lock retransmits each group of data 5 times. Accuracy of data received.
In addition, in order to save memory, it is necessary to use preprocessing technology for the received data, that is, after each received data, first compare the data with the set threshold value, if it is greater than the threshold value, an over-limit alarm will be issued; if it is less than If the threshold value is set, the data will be compared with the similar data received on that day, and the larger one will be reserved. In this way, the data stored every day is the largest value in the same kind of data.
These three key technologies can effectively improve the safety and reliability of smart locks. Each Smart Lock must be designed in strict accordance with the standards of these key technologies. If you have technical control friends, you can learn more about them.
