555 mono (restriction on Resistance value)

Discussion in 'The Projects Forum' started by vinodquilon, Feb 20, 2010.

  1. vinodquilon

    Thread Starter Member

    Dec 24, 2009
    Find the attachment (http://www.scribd.com/doc/27157788) . The purpose of the circuit is to turn on reed relay for 60sec, when
    first ring_signal occurs. For that I have to use C= 100 uF & R= 560 K. But somewhere I have
    read, in the design of 555 mono take R= 10 K to limit current through the internal transistor
    to 1 mA.
    Is it correct ? Can I use 560 K ?

    It is my first time experience with Eagle to draw schematic. If someone notice any drawing faults
    in my schematic, pls inform me to improve my drawing skill with Eagle.....
  2. Wendy


    Mar 24, 2008
    Looks good to me. Pin 7 is a simple transistor switch to ground, so Ohm's Law is in effect for the current. Figure around 100ma max (don't remember the exact spec).

    You can increase the resistances on the input quite a bit to reduce current draw, but it is a matter of taste. I'd go with 10KΩ.
  3. vinodquilon

    Thread Starter Member

    Dec 24, 2009
    Simple PICAXE-08 program to create accurate 60 sec output time delay when first ring trigger occurs.

    if pin3=1 then holdoff
    goto start

    high 2
    wait 60
    low 2
    goto start

    See the attachment. Opto-couplers' output goes to IP 3 (pin no.4) of PICAXE-08.
    I will connect IP/OP 2 (pin no.5) of PICAXE-08 to base of relay driving transistor BC547.
    Thus I can accurately turn on relay for 60 sec when first ring signal comes.

    I am newbie in the field of PIC microcontroller. Thanks for all help by IanP of edaboard.

    I couldn't find any eagle libraries for PICAXE-08 on cadsoft. Does anyone have ?
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