555 timer and cap

Discussion in 'General Electronics Chat' started by itel933, Nov 9, 2010.

  1. itel933

    Thread Starter Member

    Aug 26, 2010
    38
    0
    What is the relation between the .1 cap (connected to trig and gnd) and the 555 timer. What is its funtion? If I put a higher value what does it do to the overall circuitry?
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,772
    931
    Sounds like its time for you to experiment some.. . :)

    Have you tried LT Pspice? It a free download circuit simulator. You place the components and use a draw tool to connect them. Right click on them and set values(10k,22uf,etc). Run the simulation,specify stop time and then use mouse to click around circuit and 'see' what the signals are doing.
     
  3. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The 0.1uF capacitor is discharged then when the battery is connected the capacitor causes pin 2 to be low which starts the timer. The 33k capacitor quickly charges the 0.1uF capacitor so that pin 2 is high allowing the timer to time-out. If the 0.1uF capacitor has a much higher value then the timer will never time-out.
     
  4. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,535
    [​IMG]

    This is a power up delay. You are triggering a monostable from the power up of the circuit. Look familiar?
     
  5. itel933

    Thread Starter Member

    Aug 26, 2010
    38
    0
    So whats the highest I can safely go. I notice that if I put a small value that the micro vibrator has a tendency to turn on immediately after I turn on the unit.

     
  6. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Doesn't the circuit work properly with 0.1uF as the capacitor and 33k as the resistor as is shown on its schematic?

    On another thread or on another website I asked if the 50M resistor (it is not a standard value and is much too high) works properly?
    Did the Red LED burn out?
    Do you have an ordinary 555 or a Cmos 555?
     
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