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Phone Broadcast circuit

2016-02-13 23:01  
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This article describes a telephone broadcast circuits. The circuit is simple, inexpensive, and effective. As long as Duokanjibian The schematic can master the principles of it. This circuit can be used as a wireless telephone amplifier. You want to know the circuit derive its power directly from the active telephone lines, thus avoiding the use of any external battery or other power source. This not only saves a lot of space for repayment. It consumes very low current from the telephone line without disturbing its performance. This circuit is very small, can use a single integrated circuit type veroboard, can easily be mounted on a telephone connection box 3.75 cm * 5 cm. The circuit consists of two parts, which automatically switch section and FM transmitter section.
Automatic switching section includes resistors R1 to R3, preset VR1, the transistor  T1 and T2, the zener diode D1, D2. Resistors R1, together with the preset VR1, as a voltage divider. When the voltage across the telephone line is the 48 v DC voltage at the wiper VR1 preset range from 0 to 32 v (adjustable). Circuit switching voltage depends on the Zener breakdown voltage (here 24 v) and switching voltage transistor T1 (0.7 v). Therefore, if we adjust the default VR1 overcome 24.7 volts, which causes the Zener breakdown, for transistor T1. Results collector transistor T1 will be pulled to the negative supply, cutting off the transistor T2. In this stage, if you lift the mobile phone, the line voltage down to about 11 v and the transistor T1 interrupt. Thus, the forward-bias transistor T2 through resistor R2, the transistor T3 to provide a DC path for the following part of the FM transmitter. In part by low-power FM transmitter oscillator transistor T3, the coil L1, and some other components. Common emitter transistor T3 is the RF oscillator transistor T2 as electronic 'on / off switch. Audio signals can be adjusted automatically through the telephone line through the transistor T2 oscillator frequency together with its series bias resistor R3. Modulated RF signal is fed to the antenna. The call can be heard on FM Receiver Remote when it is tuned to an FM transmitter frequency.



Phone Broadcaster



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