timing a peizo buzzer with a lm555

Discussion in 'Digital Circuit Design' started by RBDUFFER, Sep 20, 2016.

  1. RBDUFFER

    Thread Starter New Member

    Sep 17, 2016
    6
    0
    A friend has a 120 volt converter on his truck and asked me to make a warning beeper to indicate when it is turned on.

    It should beep roughly 2 seconds off and then one second on.

    I have a bunch of small power supplies from PC speakers, Modems, answering machines, etc. in the range from about 3 to 10 volts and 100 to 1000 Ma.


    There are a number of websites showing how to computer R1, R2 and C1 to get this timing.


    Here are the Piezo buzzer specs
    Operating Voltage 3-24V
    Rate Voltage 12 V DC
    Buzzer Type Piezoelectric
    Frequency 3900±500Hz[​IMG]
    Termination Lead Wire
    Drive Method Drive Circuit Built-in
    Sound Pressure Level 87/30dB
    Max Current Rating10mA

    Please see the attached schematic in pdf format

    Can I connect points AA, BB and CC on Fig 2 to the corresponding points on Fig 1 ?

    Can I connect points BB and CC on Fig 3 to the corresponding points on Fig 1 ?

    Are current limiting resistors needed anywhere. ?

    What cautions/suggestions do I need to observe to prevent unwanted side effects. (like maybe blowing up his truck).


    Thanks in advance.
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    Almost. BB to BB requires a 4.7K resistor.
    Yes, direct connect.
    Not much. An inline fuse will make you feel safer, anything between 0.1A and 1 A.

    For the on time to be less than the off time, you'll need fig. 2, not 3. You can direct connect fig 3 if the 555 timing components are modified with 1 or 2 small signal diodes. The piezo will be fine either way.

    ak
     
    RBDUFFER likes this.
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,176
    397
    Maybe another way is ( Fig 1 & 3 ) connect AA to Buzzer BB & BB to CC; when output is low, buzzer on
    If timing Rs are about 100k ea. C = 10 uF, then pin 3 high for about 2 sec., buzzer off, C charges to 8 V, 555 resets in about 1 sec., pin 3 low, buzzer on. Buzzer might be at a low level when pin 3 high as pin 3 does not completely reach Vcc, 12V.
     
  4. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
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    DUH!!! (feel like a dummy).

    ak
     
  5. RBDUFFER

    Thread Starter New Member

    Sep 17, 2016
    6
    0
    Maybe another way is ( Fig 1 & 3 ) connect AA to Buzzer BB & BB to CC; when output is low, buzzer on


    I am not sure I undestand this. Doesn't this connect Vcc to Ground ?
     
  6. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,176
    397
    This would be easier if each lead had its own letter. Vcc thru buzzer to ground via 555, pin 3.
    Connect buzzer + to Vcc, buzzer - to 555, pin 3.
     
  7. RBDUFFER

    Thread Starter New Member

    Sep 17, 2016
    6
    0
    OK, I understand.

    Thank you
     
  8. RBDUFFER

    Thread Starter New Member

    Sep 17, 2016
    6
    0
    Thank you all.
    I connected the buzzer from pin 3 on the 555 timer to ground and it worked perfect.
     
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