The initial stage of the building intercom system adopts non-visual building intercom, which is divided into two types from the use function: direct press type (that is, the door number is on the key) and coding type. The direct binding mode is divided into two kinds: multi-wire system and bus system. The encoding system is mostly bus system.

Direct multi-wire building intercom: generally use 4+n wire system (n is the number of households), that is, each household enters the household for 5 core wire, and the main trunk line for each household a core dedicated number line +4 core bus, the early 12 households generally use AVvR16*0.15 as the main line, the main function of each core main line :1\ host to the extension,2\ extension to the host (including positive power supply voltage).3\ unlocking special wire.4\ ground wire. With the emergence of two-way communication integrated circuits, some manufacturers changed the 4+n wire system to 3+n wire system. That is, the unlocking line is incorporated into the call between the host and the extension, and the ground-to-ground unlocking method is mostly used. And most of them ring when they press the button, and stop ringing when they release the button. With the use of Ding Dong doorbell pieces, the call button was later added to the direct-press model with three rings. When the chord music IC appears, the part is changed to a pleasant chord note. Most of the wiring methods are still 4+n wire system, and some manufacturers have changed to 3+n wire system.

Direct press bus system building intercom: with the advent of remote control chips, some manufacturers will be used in building intercom, such as VD5026 and VD5028 applications. This kind of intercom generally adopts 4-core bus mode or 5-bus mode. Each core wire function takes 4 bus as an example :1 extension power supply power line,2 call line (using half duplex call mode) including call decoding signal,3 ground line,4 unlock special line. Various ringing modes adopt chip decoding to output high and low levels to trigger the doorbell piece to emit sound.

Coded building intercom: With the emergence of high-rise buildings in the city, the capacity of direct-to-type building intercom systems cannot meet the requirements, so some manufacturers have launched coded non-visual building intercom systems. Some of the earliest products use the multi-audio dialing integrated IC in the telephone and some digital ics such as 4011 to encode each pin of the remote control coding chip. Then the decoding chip is used to solve the high and low levels and the rest of the working principle is the same as the four-bus direct press type.

With the application of MCU in building intercom system, building intercom system began to open the technical distance. The development cost of some manufacturers has been increased. There are various types of intercom systems, such as the two-wire system, directly using MCU for two-way codec. Due to the application of EEPRO, there is a direct encoding by the host computer without using the old 8421 code or binary code encoding of the original remote control chip. However, due to cost reasons, the non-visual intercom system has not been able to break away from the traditional wiring mode and go to the road of full digitalization.

As developers expand the construction of the community, building intercom system manufacturers have added networking management functions on the basis of the original, which can carry out two-way call functions with the security room. Some manufacturers have launched a multi-defense area alarm function, no matter how the model is changed, but its wiring mode will not change. After adding the alarm function, because the probe power supply should be provided by the intercom, the probe power supply is added on the basis of the original 4-core wire.

Product recommendation: non-visual building intercom system in the number of households below 14 households in fact, can use the direct multi-line system, its product economy, simple structure, the more simple its failure rate is lower. For the alarm type of non-visual intercom, its use value is not high, the reason is that once the security room is called, the security personnel often have the problem of improper operation of the owner, and some owners have never used this thing, which is more inconvenient for large communities, it is not as practical as only networking two-way call calls.

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