Free Electronic Circuits & 8085 projects

Electronic projects with circuit diagram and 8085 microprocessor projects.

Telephone combined – ears circuit for home security

Published on Mar 14 2011 // DIY Telephone Circuits

Telephone combined - ears circuit for home security.

Home telephone fitted with the device to have the "ears" function, when you’re out, no one at home, if you do not trust the security of home, just dial the home phone, home, collect all sounds at the end of all ring , are able to remove your worries!
  Rapid development of modern science, to bring a convenient and affordable, in recent years a variety of phones on the market after another, there is a remote video telephone, automatic alarm call, you can access and browse the phone … …, but these new Telephone expensive, non-salaried employee can enjoy. This paper describes the electronic enthusiasts an "ears" small circuit, as long as friends can be a bit of hands-on production capacity, and the circuit is simple, easy to find components, the cost as long as ten dollars, for lovers hands it a try.
  "Ears" of the circuit, see Figure below. "Ears" circuit boards, small size, can be fixed inside the phone. Appropriate position in front of the phone 3mm drill a small hole, in which an electret microphone mounted on the handle in BM2 and BM1 telephones in parallel, two normally open relay contacts K1 K1-1, K1- 2 (circuit not shown) in parallel with telephone hook the two contacts on the telephone, install a double switch sides S1, control the external +12 V power supply and the speaker off.
  When the phone rang at home, the ringing signal is rectified by the VD1, VS SCR triggering unidirectional conduction, the work of the relay K1 is energized, normally open contacts K1-1, K1-2 is closed, telephone hook, in BM2 polar body was electric microphone to work, you can hear the ring in a variety of home, while normally open relay contacts K1 K1-3 closed, by the delay circuit composed of NE555 was electric work, then the {3} NE555 Output pin low voltage, relay K2 release, after a few minutes of delay (this time can be changed by adjusting the RP1), NE555’s output {3} pin high potential, the work of the relay K2 is energized, the normally closed contact K2- 1 Disconnect the relay K1 off the release, the normally open contacts K1-1, K1-2 break, telephone hang up, the normally open contacts K1-3 off, and power outages caused by delay circuit, following K2 release electrical power, the normally closed contact K2-1 pull, the entire circuit is restored, wait for the next job.
  Power switch S is in "OFF" position, power off, S1-2 ON, does not affect the normal telephone use, the switch S is in "ON" position, S1-1 connected, the circuit is energized work, light-emitting diodes VD3 shiny, S1-2 off, speaker phone does not ring.