July 12, 2023
Visual intercom is a complex of modern services for prosperous residential buildings, providing two-way visual communication between visitors and residents, dual image and voice recognition, thereby increasing security and reliability, saving a lot of time and improving work efficiency. .
The main applications of video intercom
Visual intercom used in one or more residential buildings, multiple households share master at door, commonly referred to as visual intercom system, building visual intercom system; and used in a single home, such as a villa, commonly referred to as single-family video intercom or villa video intercom.
Visual intercom is mainly used in individual apartment buildings or villas in foreign countries, so there are not many Internet-connected video intercom systems, while home video intercom systems are usually used in large residential areas. Many residential areas with thousands or even tens of thousands of households have higher requirements for bandwidth and stability of networked households. The mainstream of video intercom system is still use of RS-485 bus signaling, and trend is towards digital development. systems with larger households and bandwidth using TCP/IP are slowly maturing.
Currently, video intercom is widely used in urban residential buildings around world. Its manufacturers are mainly concentrated in Shenzhen, Guangzhou, Shaoguang, Guangdong Province, China, where security industry is relatively developed, and Xiamen, Fuzhou, Fujian Province, China Wait City.
Wiring diagram and working principle of visual intercom access control system (image source network)
The following figure shows main circuit of intercom doorbell, and second figure shows part of internal telephone.
The low voltage AC output from secondary of transformer is bridge rectified, filtered by a capacitor, and voltage stabilized by 7812 to produce +12V DC, which is supplied through Vl connector, one path directly supplies power to relay K. , and other path isolated D3 to generate VCC to power other circuits.
When someone on street presses one of buttons S1~S10, such as S1, base of Q5 passes through R17, socket V6①pin through Sl, phone switch SA②,③pin, and speaker LB goes down to ground, generating a current. The channel is equivalent to ground of bottom end of R17, so base of Q5 is very low, Q5 is saturated and on, music pin lC② has a high level trigger, and its pin ③ outputs music signal, which is amplified with Ul (LM386), and then output with Ul pin ⑤, through pin V6 ①, Sl, reed switch SA ②, kThe contact ③ of phone is sent to speaker LB to make a sound. Due to special design of SA telephone switch, audio signal can also be connected to ④ pin of SA telephone switch, and then connected to U2 (TDA2822M) pin ⑦ through V3 pin ② of socket, and then output from ① pin after amplification, so that person who presses on doorbell, could also hear sound of LB1. After owner heard LB's voice, he picked up phone and two people inside and outside house could talk. The audio signal received by MIC1 is sent to ⑥ pin of U2, amplified and output to ③ pin, through V3 connector ① pin, C3 on phone, SA phone switch ①, ③ pin is connected to LB speaker, owner can hear voice of other party. After VCC is lowered by main circuit resistor R5, it supplies power to MIC2 and Q1 of internal phone through connector pin V3②. The host's voice is picked up by MIC2, amplified by Q1, and then sent to U2 through SA switch ④ and ⑥, and through V3 ② to U2 ⑦. sound, thereby realizing a conversation between two people.
After owner removes phone, path from V6① pin of connector to ground is cut off, lower end of R17 returns to high level, Q5 is cut off, and music chip and Ul stop working. . V3 socket contact ① is normally high due to release switch SB tripped, regulator tube ZD1 is broken, Q1 is saturated, Q2 is off, and door cannot be opened if relay K is not working. don't get involved. When owner presses release switch SB, V3① contact is grounded, ZD1 is disconnected, Ql is disconnected, Ql collector high level is connected to Q2 base through Cll, Q2 is saturated, relay K is energized, contact is closed, and LOCK electromagnetic lock is activated. Electric movement, building door opens.
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