Laser alarm circuit help

Discussion in 'Homework Help' started by Noj123, Apr 14, 2015.

  1. Noj123

    Thread Starter New Member

    Apr 14, 2015
    3
    0
    Hi all

    I need to build a laser security circuit for a school project and was wondering if it would be possible to add a exit delay to my circuit so that there would be around 20 seconds to leave the room without triggering the alarm.

    This is the circuit i have come up with so far... sorry i am a bit of a noob when it comes to electronics and any help would be much appreciated.

    laser circuit2.png

    Thanks
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    397
    Try connecting a 555 timer output, pin 3 via diode, k to 3, anode to 400 ohm. One meg R from Vcc to pin2, & 20 uF gnd. to pin 2, 10k ohm Vcc to pin 4 ,reset. On power-up ckt will be hot, with SW pin 4 to gnd. pressing SW will reset 555 for 20 sec, disabling laser from opening 400 ohm ckt.??
     
  3. Noj123

    Thread Starter New Member

    Apr 14, 2015
    3
    0
    Thanks for your reply. I am a bit unaware of the 555 timer.. is this how it should look? i am not sure where i should actually include this in my current circuit and where i should connect the output of pin 3 to.

    555 timer circuit.png
    Thanks
     
  4. Noj123

    Thread Starter New Member

    Apr 14, 2015
    3
    0
    Managed to solve the problem now. Thanks for your help.
     
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