I need some advice, newbie here.

Discussion in 'Digital Circuit Design' started by msarian, Sep 25, 2017.

  1. msarian

    Thread Starter New Member

    Sep 25, 2017
    12
    0
    Hello,

    I need to create a circuit that will make a small speaker go off when the power source (24 Watts Max) is disabled and then a battery takes over. Speaker needs to sound no more than 15 seconds.
     
  2. Sensacell

    Moderator

    Jun 19, 2012
    2,361
    760
    What does "go off" mean?
     
  3. msarian

    Thread Starter New Member

    Sep 25, 2017
    12
    0
    A DC speaker to sound intermittently for 15 seconds.
     
  4. ScottWang

    Moderator

    Aug 23, 2012
    6,714
    1,033
    How are the V/I ?

    Use two 555 or one 556, the first 555 is a monostable multivibrator when it triggered then it will turn on for 15 seconds, and the second 555 is a astable multivibrator to drive a buzzer, works as 2 Hz oscillator.
    555 monostable multivibrator.
    555 astable multivibrator.
     
  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    9,945
    2,408
    By "DC speaker" do you mean an audible alarm?
     
  6. msarian

    Thread Starter New Member

    Sep 25, 2017
    12
    0
    V/I?
     
  7. ScottWang

    Moderator

    Aug 23, 2012
    6,714
    1,033
    V = Voltage , power supply
    I = current, A, mA
    How many volts of the circuit? (5V,9V,12V,24V)
    How much current (mA) the circuit draw?
     
  8. msarian

    Thread Starter New Member

    Sep 25, 2017
    12
    0
    Basically, all I want to do is create a device that I can plug into a USB charger (PC or car) and when the power is on, the small speaker (audible device) remains off. When the power goes out, I want the speaker to sound.
     
  9. msarian

    Thread Starter New Member

    Sep 25, 2017
    12
    0

    12V
    (mA) unsure at this time.
     
  10. ScottWang

    Moderator

    Aug 23, 2012
    6,714
    1,033
    12V Power source disable → 12V Battery on → 0.1uF/25V → npn inverter → 15S 555 monostable multivibrator → 2 Hz 555 astable multivibrator → 12V Buzzer

    >USB charger
    Is this needs to use a dc-dc (5V to 12V) converter?
     
    msarian likes this.
  11. msarian

    Thread Starter New Member

    Sep 25, 2017
    12
    0
    Scott, i'm not sure if I need a converter. I do appreciate your response above, but I guess I have to understand how to tie it all together.
    Like I said, I do not know much about electronics. I just have a great idea.
     
  12. msarian

    Thread Starter New Member

    Sep 25, 2017
    12
    0
    What component would make the battery go on when the device receives no power from the source?
     
  13. ScottWang

    Moderator

    Aug 23, 2012
    6,714
    1,033
    If the battery is 12V then you will need a 5V to 12V converter.

    The circuit below shown the trigger function and alarm(1 Hz), you can adjust the frequency of alarm, please refer to the link, I changed the bjt to N MOSFET for the power consumption of battery and using the cmos 555.

    You still need to decide how to active the battery, use plug or switch, or connected all the time but use some voltage detector to detect?

    PowerOffAlarm15S_two555_ScottWang.gif
    555 Monostable Circuit Calculator.
    555 Astable Circuit Calculator.
     
  14. msarian

    Thread Starter New Member

    Sep 25, 2017
    12
    0
    Scott,

    Thats what I'm trying to figure. The battery needs to become the source of power when this prototype gets unplugged from the 12V or USB plug.

    The power source can also be a USB port in a vehicle. I want to say the output on that is 24 Watts.
     
  15. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    9,945
    2,408
    What is the "device" that is being powered by the source or battery?
     
  16. msarian

    Thread Starter New Member

    Sep 25, 2017
    12
    0
    The device is what I'm trying to build.
     
  17. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    9,945
    2,408
    What is the battery voltage?
    How does disabling the power source cause the battery to take over? Do you have a circuit for doing this automatically?
    What is the battery powering?
     
  18. msarian

    Thread Starter New Member

    Sep 25, 2017
    12
    0
    Hi Alec,

    This device will be small. I imagine the battery will be a small lithium battery, maybe 3V.
    I would like this device to be plugged into a USB port, either my PC/laptop or in the car.
    When the device loses power, the battery needs to sound the mini speaker for 15 seconds and then shut off.
    While there's power, the speaker needs to remain off.
     
  19. msarian

    Thread Starter New Member

    Sep 25, 2017
    12
    0
    Of course, once I figure it out.
     
  20. msarian

    Thread Starter New Member

    Sep 25, 2017
    12
    0
    It almost has to be like tamper switch. When it detect no power from the source, it must switch on VIA the battery.
     
Loading...