Speech
Cordless phone CT (CORDLESS TELEPHONE) is a low-power duplex wireless telephone that is connected to the city's exchange network user. The general cordless phone has all functions of ordinary phones, such as redial, pause, hanging, hands-free, memory, etc. However, since the cordless telephone handle is wireless connection, this has determined that it has some of the characteristics of ordinary phones, such as channel conversion, identification, and more.
All major developed countries in foreign countries have invested a lot of manpower, and the material is actively conducting a development and development of cordless phones, and has quickly put commercial use. It has been developed from CT-0 to CT-3 in just ten years; from the simulation to digital; from the room to outdoor Common; developed by a single zone to multi-zoning, and can be exchanged, roaming communications, etc. Multi-channel scanning cordless telephone (CT-1), foreign developed countries began commercial use in the mid-1980s, and has developed rapidly.
1 system block diagram and principle
The CT-1 system is typically composed of a landline and a mobile phone, and the mainstline is used to establish a wireless signal connection between the landline and the mobile phone. The working mode is a non-frequency duplex.
At the current rule of the cordless telephone, the wire transmit frequency is 48/45 MHz, a total of 10 channels. Due to external electromagnetic interference, some channel communication can be poor, and the user can choose the best channel through channel conversion during use. . Identification features are very important in cordless phones, and early cordless phones are often controlled by the microcontroller, and in the microcontroller system, as long as the handle is set, it can better solve this problem. The system uses a 16-bit password with a password number of 64 k, so that system security is greatly improved.
Control landline system block diagram (Figure 1), the main function involved in the mandrel MCU is: (1) receiving the control code. The control code is sent by the mobile phone MCU. After the phone is modulated, transmitted, the landline is received, and the shaped handling is filtered, and the shaped processing inputs the machine MCU. (2) Send a control code. The control code is output by the landline MCU, and is modulated by the stand, transmitted to the phone. (3) Double-lock phase loop (DPLL) control. Initialize the phase-locked loop, transfer the phase-locked data (determined system RF frequency points) to implement RF channel selection function. (4) Dual audio generator. In fact, a DTMF subroutine in the MCU is actually in the MCU. As a civilian product, it is required to require large quantities, low cost, high quality, need to take various measures to reduce costs. In fact, there is already mature, itself with a single-chip product of the hardware DTMF generator, but the price is high. The software is used to generate a DTMF signal, and the same functions can be implemented using a common general MCU. (5) Ringing detection. Testing if there is a bell stream from the mission network. (6) Relay control. Used to control line picking and pulse dialing. (7) Other signals and signal control. Such as a channel number display control, transmit circuit power control, transmission loop, and receiving loop audio closed control, pulse / dual-tone multi-frequency dial mode conversion control, etc.
The mobile phone system block diagram and the landline are similar, and the difference is some modules that are unique to the phone. The main functions of the MCU include 1, 2, 3 of the above-mentioned landline, including mobile phone power control, keyboard scan control, mobile phone ringing signal, various LED control (call instructions, low voltage instructions), charging detection, Battery low pressure detection, etc.
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Figure 1 block diagram of the landline
This article briefly explains two modules with both the landline. One is a voice processing network, which includes both an audio filter and a pressure-extension, the former usually forms a second-order low-pass network by op amp (such as LM324), the latter uses TA3 1101 integrated block; another DPLL double phase The loop, this paper uses the MC145162 integrated block, which is a universal programmable double-lock phase ring, mainly used for CT-1 products.
2 Single Chip Microme COP840C
And the general industrial control system is different, the cordless telephone system requires low cost as a civilian product, and as mobile communication products require small power consumption and low operating voltage. The author uses the COP840C microcontroller of American National Semiconductor Corporation (NS), which has the characteristics of low cost (suitable for civilian products), small power consumption (suitable for handlers). The following is a simple introduction.
COP840C is the 8-bit microcontroller produced by NS, its main characteristics are: 8-bit CMOS processor; low power, full static; I / O and register are mapped to data memory address space; 2 KROM, 128 Byteram and 23 I / O port; variable, software can set I / O; 16-bit universal clock, with a related 16-bit automatic load / capture register; three modes of clock work: 1PWM; 2 external incident count; 3 Independent capture registers; three interrupt sources: external interrupts, clock interrupts and software traps interrupts. Detailed performance, you can see the relevant manual of NS. , Reading the full text, the technology area
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