Design And Implementation Of The Building Digital Intercom System Based On DPMR Protocol

As the rapid development of intelligent building intercom in recent years, more and more intelligent residential and community have appeared. The building intercom system has won the praise of many consumers and developers. From the perspective of consumers, building intercom system should be user-friendly and has a high performance, while meeting the basic functions. But the current intelligent building intercom products have many defects, such as complexity, low operability and high cost. Considering the cost, productions of small and medium-size intelligent building intercom are not many. According to the specific design requirements of the market, this paper makes an attempt at designing a low cost intelligent residential building intercom system, meeting the requirements of reliability, cost-effective and power consumption.The design of intercom system is based on the special digital wireless interphone dPMR protocol. Firstly, the dPMR protocol architecture is briefly introduced according to the simplified OSI layer model. Then based on the study of three layered model of dPMR, its business channel frame structure, communication mode and type of business are analyzed. At last, the basic call state and message flow are described in detail.This paper basically completes the design of building intercom system, introducing the hardware parts of LT1801A baseband chip, the external storage, CODEC module, RF module and peripheral interface circuits. The peripheral interface circuits include the MIC input, audio output, encryption circuit interface and so on. Software development environment is based on the ARM CPU ADS 1.2, using own writing and reading frequency and control software. We also describe AT signaling and each function with the code in detail.Under the normal temperature environment, the design system is tested from electric power index, the menu functions and call test. The test results show that the system meets the dPMR protocol standard, which completes the digital interphone individual call and group call function with a good quality of conversation. Furthermore, the communication distance is about 90m, which verifies the feasibility and practicability of this design.