1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Please help modified a circuit

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by cannibal, Sep 27, 2007.

  1. cannibal

    cannibal New Member

    Joined:
    Sep 24, 2007
    Messages:
    101
    Likes:
    0
    Hello

    I am using Dark activated circuit which is in black color in the attached image

    but I thought it would be better to use buzzer with timed one

    so I added other circuit which is blue color in the attached image
    it has 555 IC

    1) I would like to know if the circuit will work or not so I won't lose money buying components

    2) how to make the whole circuit working with B1 or B2 only NOT two source?

    3) what value should be for R9 ???
     

    Attached Files:

  2. ljcox

    ljcox Well-Known Member

    Joined:
    Dec 25, 2003
    Messages:
    3,205
    Likes:
    28
    Location:
    Melbourne Australia
    It won't work because the 2 circuits are only joined at one point.

    You have not explained what you're trying to do.

    You can easily run it from one battery. Just connect the 0V and V+ lines.
     
  3. cannibal

    cannibal New Member

    Joined:
    Sep 24, 2007
    Messages:
    101
    Likes:
    0
    The circuit will active the buzzer when there is no light on photo resistor

    I modifiy it again please check
     

    Attached Files:

  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,445
    Likes:
    937
    Location:
    Canada, of course!

    The 555 draws a fair amount of current even if it is not doing anything. A Cmos 555 (LMC555, TLC555 and ICL7555) draw almost no current.

    The 555 does not time out when its pin 2 is low. Add a coupling capacitor to pulse pin 2 low then use a pullup resistor.
     
  6. cannibal

    cannibal New Member

    Joined:
    Sep 24, 2007
    Messages:
    101
    Likes:
    0
    I have this type

    IC

    D&P
    NE555
    0531


    Do I have to add something ??

    and could you please show me how to add a coupling capacitor to pulse pin 2 low then use a pullup resistor
     
  7. ljcox

    ljcox Well-Known Member

    Joined:
    Dec 25, 2003
    Messages:
    3,205
    Likes:
    28
    Location:
    Melbourne Australia
    You should remove R10 and D2. These should not be in series with the battery.

    Do you want the LED to glow when the Buzzer is sounding?
     
  8. cannibal

    cannibal New Member

    Joined:
    Sep 24, 2007
    Messages:
    101
    Likes:
    0
    I fixed the LED and R10

    the circuit is working but not correct


    this what happens

    when there is light there is some low sound from buzzer which should not be

    when there is dark the buzzer sound louder which is correct
     
  9. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,445
    Likes:
    937
    Location:
    Canada, of course!
    If Q8 is connected upside down then it would act like a 7V zener diode in series with the buzzer and make it have a low level sound.

    Then when it turns on it will have a small amount of current gain which makes the buzzer a little louder.
     
  10. cannibal

    cannibal New Member

    Joined:
    Sep 24, 2007
    Messages:
    101
    Likes:
    0
    Hi

    I just fixed the circuit problem

    Now it’s working like I want

    But still one more problem

    When switching the 9V ON, the buzzer starts making sound even if there is light on photoresistor
    but it will stop after some time because of 555IC and then the circuit functioning with no problem


    HOW can I solve the buzzer problem (when the circuit starts up) ????
     

    Attached Files:

  11. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,445
    Likes:
    937
    Location:
    Canada, of course!
    Now you have pin 2 of the 555 at a low voltage all the time. With pin 2 low then it makes its pin 3 high which turns on Q3 and the buzzer all the time.

    Pin 2 of a 555 must be pulsed low for a moment to trigger it then it must return to being high.

    The signals at the emitters of the transistors are at a very low level. The trigger pin 2 of a 555 needs a high signal level.
     
  12. cannibal

    cannibal New Member

    Joined:
    Sep 24, 2007
    Messages:
    101
    Likes:
    0
    Could you please show in the diagram
    because I couldn't follow
     
  13. cannibal

    cannibal New Member

    Joined:
    Sep 24, 2007
    Messages:
    101
    Likes:
    0
    Yes the buzzer now sounds all the time !!

    I am now confused :(
     
  14. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,445
    Likes:
    937
    Location:
    Canada, of course!
    Pin 2 of the 555 is connected to a 47 ohm resistor (R6) to ground. Its voltage is about 0.08V. Pin 2 needs to be at least 6V for the 555 to time-out.
     
  15. cannibal

    cannibal New Member

    Joined:
    Sep 24, 2007
    Messages:
    101
    Likes:
    0
    how can I make it 6V ??!!!
     
  16. cannibal

    cannibal New Member

    Joined:
    Sep 24, 2007
    Messages:
    101
    Likes:
    0
  17. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,445
    Likes:
    937
    Location:
    Canada, of course!
    Is this what you want?
     

    Attached Files:

  18. cannibal

    cannibal New Member

    Joined:
    Sep 24, 2007
    Messages:
    101
    Likes:
    0
    hello

    I tested the circuit you provided in breadboard

    I faced these problems

    1) the buzzer making sound when there is light and that should be revered
    the buzzer should make sound if it's in dark

    2) the buzzer not stoping making sound

    3) the sound of the buzzer is too week
     
  19. ljcox

    ljcox Well-Known Member

    Joined:
    Dec 25, 2003
    Messages:
    3,205
    Likes:
    28
    Location:
    Melbourne Australia
    I don't see why you need Q3 and R8.

    Connect the buzzer to the 555 pin 3.
     
  20. cannibal

    cannibal New Member

    Joined:
    Sep 24, 2007
    Messages:
    101
    Likes:
    0
    hello
    with out Q3 and R8 it won't work

    Mr audioguru

    I tried to test again your circuit and it's working fine
    but facing one simple problem

    1) the buzzer won't stop when it get activated :(

    I appricate your help
     
    Last edited: Sep 29, 2007
  21. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,445
    Likes:
    937
    Location:
    Canada, of course!
    In my circuit the 555 is a monostable exactly like in its datasheet. The 10k resistor holds its pin 2 high so it can time out and stop the buzzer.

    When it gets dark then Q1 turns off. Then R4 turns on Q2. The collector of Q2 then has a negative-going pulse through the 47nF capacitor that triggers pin 2 of the 555 so it makes a timed output for the buzzer. R4 and R9 are 10k ohms and R5 is 470 ohms.
     

Share This Page