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Video intercom access control system principle and wiring diagram
Source: Smart Soft Last updated: 2016-7-28 9:36:04

Video Intercom Access Control System Principle

The figure below is the main circuit of the intercom doorbell , and the second figure is the indoor phone part.

The AC low voltage of the transformer secondary output is bridge rectified, capacitor-filtered, and 7812 stabilized to obtain a + 12V DC voltage. It is directly input to the relay K through the socket V1 input, and the other is isolated by D3 to generate VCC to power other circuits.

When someone presses one of the buttons S1 to S10, such as Sl, the base of Q5 passes R17, socket V6 ① through Sl, phone switch SA ②, ③, and the speaker LB reaches the ground, forming a current path, which is equivalent. Since the lower end of R17 is grounded, the Q5 base is extremely low, Q5 is saturated and turned on, and the music lC② pin has a trigger high level. Its ③ pin outputs a music signal, which is amplified by Ul (LM386) and then output by Ul⑤ pin, via V6① Feet, Sl, the phone and spring switches SA②, ③ feet to the speaker LB to make it sound. Due to the special structure of the phone switch SA, the audio signal can also be coupled to the phone switch SA④ pin, and then to the U2 (TDA2822M) pin via the socket V3② pin. After amplification, it is output by the ① pin, so that the doorbell can also hear LB1 Make a sound. After the host heard the sound from LB, he took off the phone and the two people in the house and outdoors could talk. The sound signal picked up by MIC1 is sent to U2 ⑥ foot, which is amplified and output by ③ foot, which is coupled to speaker LB via socket V3 ① foot, C3 on the phone, and phone switches SA① and ③ feet. The host can hear the other party's voice. After VCC is depressurized by R5 of the main circuit, power is supplied to the MIC2 and Ql of the indoor phone through the V3② pin of the socket. The voice of the host is picked up by MIC2 and amplified by Ql, and then sent to the U2 jack via the switches SA④ and ⑥ of the phone, and the jack V3②. After amplification, it is output by ① and pushes the speaker LB1 to make a sound, thereby realizing the conversation between the two.

After the host took off the phone, the path from the foot of the socket V6① to the ground was cut off, the lower end of R17 returned to a high level, Q5 was cut off, and music lC and Ul stopped working. Socket V3① foot is normally high because the unlock switch SB is disconnected. Zener ZD1 is in a breakdown state, Q1 is saturated, Q2 is turned off, and relay K cannot be closed without opening the door. When the owner presses the unlock switch SB, the V3 ① pin is grounded, ZD1 is turned off, Ql is turned off, the high level of the Ql collector is coupled to the Q2 base via Cll, Q2 is saturated, the relay K is powered, the contact is closed, and the electromagnetic lock LOCK is Electrically operated, the building door opens.

Video intercom access control system wiring diagram

Video intercom access control system principle and wiring diagram
Video intercom access control system principle and wiring diagram

Video doorphone doorbell fault repair

Press any key from Sl to Sl0, if you can hear the door bell, it means that Q5, music IC and Ul are basically working normally.

The two parties can talk, indicating that the U2 and the indoor phone are working normally.

Socket V3 ① The feet are normally high potential. ① When the feet are shorted to ground, if you can hear the sound of relay K, the unlocking circuit is normal.

The building door intercom system has many discrete components and complicated circuits, but with the schematic, maintenance is easy.

Due to the low supply voltage, the failure rate is not high. Electromagnetic locks are frequently used, so they are easily damaged. During maintenance, if you can hear the closing sound of relay K, but the electromagnetic lock does not work, it can be considered that the electromagnetic lock is damaged. In addition, the main circuit is prone to open welding failure due to vibration.

If any part of the circuit is abnormal, first check the power supply part. Because the interface of each part is clearly marked, it is generally easy to troubleshoot the motherboard, the keypad, and the phone for maintenance.

Example 1: ZD2 breakdown, no door bell, but somehow, when the unlock switch SB is pressed, the sound of K is not heard, and the fault is removed after changing to a new K.

Example 2: Can't talk. It was found that U2 (TDA2822M) was damaged, and it was damaged shortly after the renewal. It was found that the VCC voltage was 16V, which was higher than the maximum power supply voltage of TDA2822M 15V. It was finally found that the 7812 breakdown of the power board was estimated to be overheating damage. Replace it with a new one and increase the heat sink for troubleshooting.

Example 3: The doorbell doesn't ring when you press individual buttons. Generally, it is a malfunction of the buttons. After the replacement, the malfunction can be eliminated.

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