How is the key to the doorphone arranged and why does it work
Well, when the entrance to the apartment building is equipped with an intercom: no strangers, clean entrance. Using this device every day, we no longer think about how the lock works and why our key does not unlock the neighboring doors. It is believed that the keychain contains a magnet, but imagine: this is not true! The principle of operation of the intercom is based on a completely different technology.
What's inside the key
The key is a read-only memory device inside which the code (serial number) is stored. When contact with the lock occurs, information from the key fob memory is read out and the door opens.
The key memory is non-volatile. The most common type of memory is Touch Memory. Information is exchanged with the intercom using the One Ware protocol (single wire): interaction occurs simultaneously with several devices and transfers power to these devices through a single channel.
At the time of communication with the intercom module, short-term power supply to the storage device occurs due to the capacitor built into the key fob. The main unit periodically gives a signal (at least once every 120 microseconds), supporting the necessary charge level and power supply of the key chip. The intercom keychain does not create any impulses on its own.
How is the main unit
The intercom module operates in standby mode and periodically sends signals to the key. Upon contact with the lock, the key fob waits for such a signal and generates a pulse that allows the main unit to establish communication. Then the intercom module starts reading the key memory, identifies its serial number and unlocks the corresponding door. Therefore, even if the whole house is serviced by one company, residents cannot penetrate other people's entrances.
The principle of operation of the main unit does not change, but for different manufacturers the "filling" of the key has differences in characteristics. That is, a specific intercom unit can work only with a certain type of key fobs.
Why does the right door open
Upon contact with the key, the circuit closes and a channel is created for reading information. The main module receives it in the form of pulses. In total, 64 bits of information are received, that is, the number of generated pulses is 64.
The system works by transmitting different intervals of release and circuit closure. If the key needs to pass a logical zero, then it "nullifies" the bus. When transmitting a logical unit, the key is silent.
The intercom analyzes the received data and compares them with the list. The lock opens when the module finds a match. The key serial numbers (codes) are added to the list by the installation company during installation of the device.
If something went wrong
The operation of the system, that is, the speed of reading information and the response of the lock open signal, is influenced by weather conditions and the technical condition of the “tablet” (level of contamination or surface damage). Therefore, you need to be careful about the keychain.
If you find that someone from outsiders has picked up a key to the doorphone of your entrance, then it is necessary to recode the lists of numbers. To do this, contact the discussion company. The same thing needs to be done if you have lost the key to the doorphone - you will be given a duplicate.
This access control system is widely used because it is inexpensive and reliable. Most likely, the keychain from the intercom will remain a familiar attribute of our daily life for a long time.
