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Phone Jewelry principle

2016-02-04 06:43  
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Next is the phone jewelry works. The most effective way is to grasp the principle of combining schematic view text, combined with text to understand the principle. See Figure: Resistor R1 and an ordinary neon light, lights form a complete visual bell circuit. This simple arrangement does not require DC blocking capacitor because, under idle conditions, the telephone line voltage is not sufficient ionized gas, so the neon lamp does not light. Only when the ring signal is received, it flashes during ringing rate to indicate an incoming call. Bridge rectifier diode D1 through D4 acts as a polarity guard used to protect electronic circuitry from any change in the telephone line polarity. Zener diode D5 Output This bridge rectifier circuit for additional protection. Part of a transistor T1, resistors R2, R3 and zener diode D6 form a constant-voltage regulator, which provides a low output voltage of approximately 5 volts. Dial tone, the speech signal from the switch is connected to the receive audio amplifier stages around the transistor T2 and the associated components, the resistors and capacitors C5, R6 R7. Amplified signal from the collector connected to a dynamic receiver transistor T2 rt - 200 (for headphones) through the capacitor C7. A condenser microphone, connected as shown in the circuit as a transmitter. An audio signal at the microphone is connected to the base through the development of the capacitor C3, the transistor T1. Resistor R4 determines the required DC bias microphone. Amplified by the transistor T1, the audio signal is coupled to the telephone line through the diode bridge. The entire circuit can be connected in a very small  PCB  and live in a medium-size headphones, see illustration. For better results in low line current, the value of resistor R2 may be reduced in the test. The principle is simple but effective. You can read several times to grasp the principle.

Telephone Headgear

Telephone Headgear

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