Description the working of Fire alarm System with Automatic Exit Door Unlock

Discussion in 'The Projects Forum' started by NTCM, Jun 15, 2014.

  1. NTCM

    Thread Starter New Member

    Apr 17, 2013
    could you please support and help ASAP to describe technically of the attached circuit

    Description the working of the circuit (How is it working)?
    Function of each elements in the circuit ?

    The idea of the circuit (Fire alarm System with Automatic Exit Door Unlock)
    a smoke detector alarm circuit connected with a relay to unlock the emergency exit door. When the sensor detects smoke, it triggers a current to flow to the relay and energized it and thus, will unlock the door
    The output of the circuit door unlock automatically + Exit light ON + Sound
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    The photo led emits a beam of light to the photo transistor, when there are smoke particles in the chamber the photo transistor turns off, turning on transistors T1, T2 which fires the gate on the thyristor T3, and latches the relay on,T4 also turns on and sounds the buzzer and puts the led D1 on. The preset P1 will allow for different sensitivity of smoke, P2 for gate voltage.
  3. eetech00

    Active Member

    Jun 8, 2013

    I would redesign the circuit so that if the circuit fails, the relay would de-energize, and unlock the exit door.
    Maybe use an OSC to generate a regularly occurring pulse that, when sensed by a detector, would maintain energy to the
    relay, keeping it energized.

    Last edited: Jun 15, 2014
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    Don't know where in the world you are, but AFIK here in the UK emergency exit doors in public buildings have to be kept unlocked if the building is occupied.
    GopherT likes this.