Smart Lock Fingerprint Recognition Working Principle

The working principle of smart lock fingerprint recognition and why the fingerprint recognition module fails when the fingers are sweaty or watery

The working principle of intelligent lock fingerprint recognition is very simple. Its principle is very similar to that of computer processing information. The workflow of fingerprint recognition is divided into the following three steps:

Step 1: After installing the smart lock, the householder needs to input the fingerprint to let the smart lock know who is the owner.

At this time, it is necessary to collect the fingerprint of the smart lock, and input the fingerprint of the family members who need to unlock permission according to the instructions. Generally, good smart locks have large fingerprint storage space, which can store dozens or even hundreds of fingerprint records at the same time. The work part of fingerprint input is equivalent to introducing the family to the smart lock one by one, so that the smart lock will remember its owner.

Step 2: The intelligent lock center processing system judges and processes the information input by the householder.

When the owner points his finger at the fingerprint acquisition window sensor module of the smart lock and presses the fingerprint, the smart lock system will photoelectric convert the fingerprint of the owner and compare the fingerprint data with the information in his fingerprint database.

Step 3: The intelligent lock center processing system makes a judgment and executes the command.

When the information matches correctly, the fingerprint record is consistent with the fingerprint record of the database, and the system judges that the fingerprint is the fingerprint of the head of the household, it is allowed to pass, and the result of processing is transmitted to the door lock through the power control box, so as to open the door, otherwise, it will not open the door.

At this point, the workflow of fingerprint lock is finished. Science has proved that everyone’s fingerprints are unique. There are not two identical fingerprints, even the fingerprints of identical twins are different. Therefore, it is very safe to use fingerprint as the “key” of door lock.


Why do sweaty fingers or water in fingers cause fingerprint recognition module failure?

At present, there are two ways to collect fingerprint, optical and capacitive (semiconductor).

1 Optical type

The optical fingerprint head obtains the fingerprint information by calculating the different distance between the light in the groove and ridge of the fingerprint and the collection window. When the finger has sweat or the collection window has water, it will affect the transmission and distance of the light, resulting in the error between the obtained fingerprint information and the original stored information, so the fingerprint lock identification fails.

2 Capacitive type

When the finger is pressed to the fingerprint collection window, because the human body is an electric field, the user fingerprint pattern and the sensor surface will form a coupling capacitance. For high-frequency current, the capacitance is a direct conductor, so the finger will absorb a small current from the contact point. This current flows out of the surrounding electrode, and the current flowing through the surrounding electrode is proportional to the distance from the fingerprint to the surrounding. The controller obtains the touch ripple related data through the accurate calculation of the current proportion. Because the water is conductive, when fingerprint identification is used when the fingers are sweaty or the collection window is stained with water, the current will be affected, so the above calculation is not accurate, and the natural identification fails.

When users of smart lock input fingerprint for the first time, they must keep their fingers and fingerprint acquisition windows dry and clean so as to input correct and clean fingerprint; when users use fingerprint unlocking, wipe their fingers and acquisition windows to avoid most fingerprint identification failures.

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