Building intercom system circuit analysis - Power Circuit - Circuit Diagram - Huaqiang Electronic Network
Many households today rely on building intercom systems for the convenience of managing access to their buildings. However, due to the lack of circuit diagrams provided with most building intercom systems, it can be challenging to maintain these systems. Having repaired several sets of such systems, I have clarified their working principles, drawn circuit schematics based on the physical boards, and created wiring diagrams. This documentation serves as a reference for future maintenance efforts.
Building intercom systems generally fall into three categories: direct-press intercom systems, digital intercom systems, and visual intercom systems. As illustrated in Figure 1, the structure of a typical building intercom system includes five main components: the main unit, multiple extensions (one per household, though only two are shown in the diagram), the electric lock, the power supply box, and the connection system.
The operation of the entire intercom system works as follows: the power supply box powers the main unit, which contains an internal step-down charging circuit and a backup battery. Once the mains power is reduced, rectified, and filtered, the battery is charged. When the mains power fails, the battery takes over the power supply. The main unit acts as the heart of the system, housing a power control circuit, a calling circuit, an intercom circuit, a video circuit, and an unlock circuit. These circuits are connected via a call line, a transmission line, a telephone line, a video line, an unlock line, a ground line, and so on, linking to each household’s extension. If a visitor wishes to enter the building, they press the corresponding household button on the main unit at the security door. This triggers a ringing sound at the household extension, allowing residents to verify the visitor via the intercom and video systems before pressing the unlock button, activating the unlock circuit and opening the electronic lock.
1. Direct-Press Intercom System
In this type of system, each household has a dedicated call button on the main unit. Each button is linked to the corresponding resident through a call line, as depicted in Figure 1. Pressing the button allows for a direct call to the resident, making it straightforward and user-friendly. However, it lacks any security features. For a building with 20 households, this setup would require 20 separate call lines, in addition to the four standard lines: transmission, telephone, unlock, and ground. While the cost of the main unit is relatively low, the connection system is expensive due to the large number of wires required.
2. Digital Intercom System
This system features a keypad with numbers 0 through 9 on the main unit. It includes a built-in code recognition system where each household is assigned a unique set of digits. To call a specific household, one must enter the correct code; otherwise, the call cannot proceed, providing a level of privacy and reducing unwanted disturbances. All users can connect to the main unit via a shared call line, with the code system identifying and connecting the caller to the intended recipient. Although the cost of the main unit for this type of system is higher, the connection system is simpler and more cost-effective, requiring just five common lines: call, send, voice, unlock, and ground.
3. Visual Intercom System
The visual intercom system further enhances communication by incorporating cameras into the main unit and adding imaging equipment to the extensions. Based on the previous types of connections, additional video signal cables or amplifiers are necessary, along with individual small power supplies for video display at each user's location.
The Lilin JB-220V building intercom system discussed in this article integrates the unlocking circuit into the main unit and shares the transmission system across a single line, simplifying wiring requirements. This innovation reduces both complexity and costs while maintaining functionality.
Understanding these different types of intercom systems helps ensure that homeowners can choose the right solution for their needs, balancing cost, convenience, and security. Whether you’re looking for a simple direct-press system or a feature-rich digital or visual option, each type offers distinct advantages depending on your priorities.
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