seconds delay timer

Discussion in 'The Projects Forum' started by jj_alukkas, Jul 8, 2009.

  1. jj_alukkas

    Thread Starter Well-Known Member

    Jan 8, 2009
    751
    5
    Hi everyone,

    I'm building a theft alarm system for my car and for the final alarm section, I need a delay ckt for 5 seconds. It is intended to run a warning buzzer to notify if I accidently left it on before the main alarm goes on.. Is it possible with a normal version of 555?? I dont want the CMOS type cos of some availabilty issues.. If 555 cant do, a transistor with capacitor would be enough just for the delay. how can i do it??
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,534
    The 555 Monostable should work, either CMOS or conventional. There really isn't much difference between them.
     
  3. jj_alukkas

    Thread Starter Well-Known Member

    Jan 8, 2009
    751
    5
    I breadboarded this circuit

    [​IMG]

    I am using a 50k resistor and 100uF capacitor instead of 100k + 1M resistor and 220uF cap.. I get a timing of 5 sec approx but most of the time I power on the circuit, the output goes low immediately instead of going low after 5 seconds.. I guess its a triggering problem.. how can I correct it??
     
  4. jsm09a

    New Member

    Jul 8, 2009
    5
    0
    You might try connecting NE555 pin 4 to pin 2 rather than VCC.
     
  5. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,534
    Let's see, 1.1 R(1E6) C(220E-6) = 242 seconds. You are talking minimum values, or you have a wiring error.

    Pin 4 is not an input for monostable, it is only for enable or disable the timer.

    You might also try the input conditioner I showed in my experiment referred to in post #2.

    With a DVM you should be able to see the voltage change on Pin6 and 7, it starts at ground (normal), then slowly charges up to 2/3 of Vcc, then resets to ground.
     
  6. jj_alukkas

    Thread Starter Well-Known Member

    Jan 8, 2009
    751
    5
    Oh the ckt works now.. it was some problem on the breadboard.. Everything is fine now.. gives 5 second high, then goes low.. Thanks bill.. have to thank u a lot
     
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