LM555 help

Discussion in 'The Projects Forum' started by jchannel, Sep 13, 2012.

  1. jchannel

    Thread Starter New Member

    Jul 15, 2009
    4
    0
    I am new to 555 and have never worked with one other than a kit. I want to build two units to control two relays. The fist is to set off an alarm sounding three times for 1 to 2 seconds each round. On the third one it turns off. The second is simple, a ten second timer to trip a relay supplying power to the rest of the project.

    Being so new to all this, I think I have over read and confused myself to what I think I know. Any help is appreciated.

    Chris
     
  2. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    First, a 555 one-shot set to clock out 6.5 seconds.
    That feeds power to the second 555 that is astable at 1 second on and one second off.
    Then there is the simple one.
     
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
    745
    Ok let me see if i understand ,

    two timers one set to astable mode (oscillating) at 1second on 2 seconds off.

    the second timer set to monstable (once only) this sets the first timer off then times out after 10 seconds and triggers your relay and stops the first timer from oscillating?
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    Use a microcontroller instead.
     
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
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    Looks like #12 has it, but seems there are 3 on's & 2 off"s, so only need 5.5 sec on first 555.
     
    #12 likes this.
  6. ScottWang

    Moderator

    Aug 23, 2012
    4,854
    767
    The following is an idea, and to be a reference.

    NE555 Monostable (About 6sec) → Ctrl Reset Pin(NE555 osc set to 0.5~1 Sec) → CD4017 Out "1","3" → Add 2 1N4148 + 10K to GND → NPN driver → Relay → Sound Alarm

    If you wish to auto stop the Monostable of NE555, then you can use CD4017 Out "6" to a NPN driver as Inveter, and from C of NPN driver to control the Reset(Pin 4) of the first NE555 Monostable.
     
    Last edited: Sep 15, 2012
  7. absf

    Senior Member

    Dec 29, 2010
    1,492
    372
    Below is the schematics constructed based on scottwang's description. Since second and third part are easy, you should be able to do it without help.

    Allen
     
    Last edited: Sep 15, 2012
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