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5-Star Wireless Alarm

2016-02-18 07:19  
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5-Star Wireless Alarm

 

Present a variety of commercially available phone alarm expensive, its principles and simple circuit, mainly to detect a voltage drop. When the phone when you hang up the telephone line so the voltage is 60V. Pick up the handset, as with the telephone load (DC resistance of about 300O or so), the line voltage down to about 8V. Alarm as long as this change is detected, the alarm signal interference.
  Circuit: As shown, the circuit by a 12V voltage regulator tube to detect. When the line is normal, added to both ends of 60V reverse voltage regulator to turn on, LED light, that line is working. A point potential at this time is about 30V, R2 provides base current to B1, B1 to B grounding conduction. Interference chip KD9561 alarm does not work. Once someone unauthorized use of phone, the external voltage is reduced to about 8V, DW1 into a cut-off by the turn. A point potential is zero, B1 closed. B2, B3 turn, interfere with the alarm circuit so that thieves can not be normal dial-up. LED2 light at this time, the speaker also issued a short emergency Y1 sound the alarm. When the user use the phone, the optocoupler circuit in series in the conduction point B can also grounded, the circuit does not interfere with police work.

2N5551 transistor, 2N5551 Application Circuits, 2N5551 Circuit Diagrams

Component Selection: KD9561 is four syllables alarm chip, simply power poles can be connected to the circuit. Optocoupler optional 4N25; B1, B2, B4 should use special telephones VCEO = 100V transistor 2N5551; B3 can be 2N5401; LED1 choice of green light-emitting diode; LED2 can choose red.