With the popularization of telephones, the telephone remote control system capable of realizing remote control of electrical equipment has attracted more and more attention because it does not occupy additional radio frequency resources and is not restricted by geographical distance. The telephone connection module PH 8810 has the characteristics of high integration, low power consumption, powerful functions and flexible use, and is very suitable for use in a telephone remote control system.
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1 How does the telephone remote control system work?
The telephone remote control system generally uses a single-chip microcomputer as a control unit, and is equipped with a circuit such as ringing detection, automatic hooking, DTMF decoding, voice prompting, and electrical equipment control driving. The working principle is shown in FIG.
When a call comes in, the system detects ringing. If it is not answered for a certain period of time, it will automatically pick up the phone and activate the voice prompt circuit. The user will use the own phone keypad to operate under the voice prompt. The DTMF decoding circuit decodes the received keyboard operation signal into a 4-bit binary number, and sends it to the MCU for corresponding processing, thereby issuing an electrical device control signal. If you enter the wrong control password multiple times or the standby time is too long during the operation, the system will automatically hang up.
2 PH8810 structure and function
PH8810 is a highly integrated telephone interface module, using a standard 40-pin DIP package, 5 V power supply, operating current ≤ 1 mA, with a unique low-power circuit design, to avoid excessive device overload Heating increases the service life of the device; the operating frequency is 300 to 3 400 Hz, and the dialing indicator conforms to the DTMF standard frequency. Integrated with ringing detection, telephone disconnection detection, automatic hooking, automatic gain adjustment, DTMF coded transmission (HT9200), DTMF receive decoding (HT9170) and other circuits; with 4 normal I/O ports (can be used as audio or DTMF) Signal input/output) and 4 I/O ports for automatic gain control (enables the input signal); a test output is configured to power other micropower systems. The internal structure block diagram is shown in Figure 2. The detailed functions of each pin are shown in Table 1.
When applied, the 8, 18, 40 feet must be connected to the power supply at the same time, 1, 32 feet are grounded at the same time; 2, 3 feet are connected to the telephone line; 3 feet and 7 feet are connected with a straight-line capacitor for ringing detection; DTMF decoding signal Output from 22, 23, 24, 19 feet; the voice signal to be loaded onto the telephone line can be input from any one of 28 to 31 when the level is large, and can be driven from the automatic gain control when the level signal is small. 10 to 13 any one foot input.
Because PH8810 has a high degree of integration, the telephone remote control system based on this module only needs to be equipped with a main control MCU, voice prompt and electrical control drive circuit. In the design, the single-chip microcomputer selects the commonly used AT89C51, the voice circuit uses the ISD company's voice chip ISD4004, and the electrical control drive circuit selects the integrated driver MC1413. The specific circuit design is shown in Figure 3. AT89C51, ISD4004 and MC1413 have a wide range of applications in various circuit designs. There are many more information about them. I won't go into details here. The following is mainly about the application of PH8810.
In the circuit, the 2nd and 3rd pins of the PH8810 are connected to the external line of the telephone. A 47 μF/240 V step-down capacitor is connected between the 3rd and 7th pins to isolate the 48 V DC in the telephone line to achieve the vibration of 90 V/25 Hz. The bell signal is detected. When there is a call, the ring detection output terminal 9 outputs a low level to the P2.4 port of the AT89C51 of the single-chip microcomputer. In order to prevent the remote call from being mishandled by the normal incoming call, the MCU delays for 10 s (by software programming). 9 feet for detection, if still low level output, AT89C51 automatically picks up the phone through P2.7 port control, and starts the voice circuit; audio output terminal of voice chip ISD4004 and PH8810 I/O port with AGC function 13 The feet are connected, and the pre-stored voice information is loaded onto the telephone line through the PH8810. After the operator receives the voice prompt through his own handset, he/she will send a DTMF-encoded control signal according to the prompt. The coded signal is transmitted to the PH8810 via the telephone line, and then decoded by its internal DTMF decoding circuit HT9130 to generate a 4-bit binary digital signal, which is output by 22 (D0), 23 (D1), 24 (D2) and 19 (D3) pins. P2.0 ~ P2.3 port of AT89C51. According to the different decoding signals received, the AT89C51 outputs the corresponding electrical equipment control signal to the relay driving chip MC1413 through the P1 port, thereby realizing remote control of the electrical equipment. In addition, the 38 pin of PH8810 is the telephone line disconnection detection terminal. If the telephone line is disconnected, the output is high level, and the telephone line connection is normal, it is low level.
The telephone remote control system uses the PH8810 interface module, with the AT89C51 as the control unit, and the ISD4004 voice chip and the MCl413 driver chip. The circuit structure is relatively simple, the stability is high, and the existing wiring pattern of the control site is not damaged at the time of installation, and After installation, it does not affect the normal use of the phone. In addition, PH8810 is widely used in telephone automatic alarm, telephone voice and data transmission systems due to its high integration and full-featured functions.
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