Production of universal mobile phone data cable

The original mobile phone data cable is expensive, which makes many users discourage it. Through the analysis and research on the data lines and schematics of Siemens, Samsung, Alcatel, Lenovo and other models, I found that the data lines of most models on the market are similar, but the interface shape and definition are different. The data lines of many models can be self-made, as long as the appropriate changes are made according to the definition of the actual model data line interface. This article takes Siemens 6688, 6618, 3618 and other mobile phones as an example to introduce the production of mobile phone data lines for your reference.

Let us first look at the definition of the computer RS232C port (serial port, as shown in Figure 1): 1 carrier detection (DCD), 2 accept data (RXD), 3 send data (TXD), 4 data terminal ready (DTR), 5 signal ground Line (SG), 6 Data Ready (DSR), 7 Request to Send (RTS), 8 Clear to Send (CTS), 9 Ringing Indicator (RI). Its signal is EIA level (-3 - -15V, +3 - +15V). The interface of Siemens 6688 and other mobile phones (Figure 2) is defined as: 1 ground wire, used for the negative pole of the charger and the ground of the data line; 2 left channel of the earphone; 3 positive pole of the charger; 4 empty, not short-circuited with other feet; 5 data OUT; 6 data IN; 7 empty; 7, 8 feet have the same function. Connect the switch (one of which is shorted first and ground, the other is connected to the switch on the earphone); 9 ground, commonly used for MIC ground; 10MIC positive; (11) Headphone right channel; (12) Headphone ground. Its signal is CMOS/TTL (0-3.3V) level. Since the electrical characteristics of the computer serial port and the mobile phone data port (TTL circuit) are different, signal conversion is necessary to enable the two to communicate with each other.

The working principle of the data line (see Figure 3): -5V to -15V in RS232C stands for 1, +5V to +15V stands for 0; while in TTL circuit, greater than 3V stands for 1, and less than 0.2V stands for 0. The MAX232 integrated circuit (MAX232 pin definition is shown in Figure 4) realizes the conversion of RS232C and TTL circuits. The 8-pin receives the TXD (transmit data) signal sent by the serial port 3-pin, and the output is output from the 9-pin to the 6-pin IO of the mobile phone. - RXD (data reception); 10 feet receive the IO_TXD (data transmission) signal sent from the mobile phone. From the 7 pin output to the serial port 2 pin RXD (receive data) and 1 pin DCD (receive line signal detection). The working power supply of MAX232 is provided by the serial port. The voltage of 12V output from the serial port 4, 6, 7, and 8 pins is rectified by two 1N14148 diodes. After the voltage is regulated by the 78L05 voltage regulator, the 5V voltage is output to the MAX232 (16) pin for integration. Block work. The 5V power supply is also sent to the 3-pin of the plug to charge the phone. If you don't want to use the charging function, you can not solder 3 pins or add a small switch in front. The four capacitor parameters of the MAX232 affect the data line transmission speed. The manufacturer's recommended value luF (0.1uF for MAX232A and MAX3232) is used here. The 470uF and 47uF capacitors are the power supply filter capacitors. If the circuit is desired to have a data transmission indication function, the indication circuit of FIG. 5 can be added.

Component selection: The core of this circuit is the MAX232 integrated block. There are two kinds of common packages, one is double in-line type, the volume is larger, and the welding is convenient; the other is patch type, and the volume is small. In addition, if you can't find MAX232, you can also use RS232 transceiver integrated blocks such as MAX232A, HIN232, MAX220, MAX3232, IL32, etc. The pin definition is the same as MAX232. The first two integrated blocks are faster. The appearance of the 78L05 is the same as that of a normal triode. Pay attention to the definition of the pin when purchasing. If it is found that the heat is severe, it can be replaced by 7805, or use a 1V voltage regulator to add a current limiting resistor instead. The welding of the capacitor should pay attention to distinguish between positive and negative. A 0.1uF CBB capacitor on both ends of the filter capacitor works better. The four parameter capacitors are preferably made of high-quality capacitors such as tantalum capacitors. The capacity of luF or O.1uF can be selected according to the integrated block. The harder to find is the phone plug, but it can be obtained from the old charger of the same type of interface, but pay attention to all metal pins must be complete. A shielded 6-conductor cable for the cable. The above materials can be purchased in electronic component stores or computer network consumables stores, and can be purchased at around 10 yuan.

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