Running two circuits in parallel off one power supply help

Discussion in 'The Projects Forum' started by big hank, Jan 3, 2010.

  1. big hank

    Thread Starter New Member

    Aug 17, 2009
    3
    0
    Hey gang! Been a long time lurker and can usually find my answers through other people's threads but I'm stuck here!

    I modify and customize action figures, and currently I am working on a Transformers tank/robot.

    I have a little dollar store LED/sound space gun toy I gripped the PCB out of to install in the tank turret. It has one red LED and a piezo for the sounds. It uses a momentary switch to cycle through 7 variations of sound and light.

    I also have a dedicated blue SMD size LED for the eyes. Running off a slider switch to turn it on and off.

    Because of the space constraint's in an action figure I want to run both circuits off one power supply (4.5v, three button cells LR44 I think).

    It all works great except when the "eyes" are on and I activate the cannon LED/sounds, the PCB for the LED/sound seems to steal the power and I lose the blue LED eyes while the other circuit is functioning.

    I have tried a resistor on the LED that is in the sound/LED module. No good, also I tried a capacitor on the "eye" LED thinking it may hold enough voltage to power it during cannon "firing", also to no avail.

    I cannot tell the IC used on the PCB because of the black epoxy dot over it. I'm thinking something like 555, because I only see 7 traces on the PCB.

    The piezo and red LED are on the same two traces on the PCB, and the pitch and light behave the same, as far as pulsing and emitting sound at the same rates.

    I can add another component if it's small enough, but I'm getting real cramped as is (Ive got the PCB under the turret, which must also share the robot's head and arms, plus the back side of the switches.

    To summarize, I want to turn the blue "eyes" on and off at will, and when on I want to be able to activate the PCB gizmo without affecting the output of the eyes LED, All running off one power source.

    Sorry for the long read folks, just trying to give as much info as I have.:D
     
    Last edited: Jan 3, 2010
  2. djb

    Member

    May 17, 2008
    18
    0
    don't you think you have to figure out the problem first ??

    if i where you, i would connect the "eyes" directly with external wires to the source. (batteries and then regulator if there is any) so you can understand if it is power problem (limit) from the source, or a PCB problem. or try with other ways to figure out where the problem is, by bypassing some parts. after that, we can talk further.
     
  3. big hank

    Thread Starter New Member

    Aug 17, 2009
    3
    0
    Did that, thanks though. I am running the eyes off separate wires at the moment. You did hit on something with the regulator, I wasn't using one. If I can shoehorn it into the space I have it may work.

    Will update tonight after I try a few things I thought of as well.

    Appreciate the help.
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Your tiny battery does not have enough power to activate the sound and light circuit plus light the two blue LEDs.

    It might work for a few minutes if the battery cells are brand new name-brand ones.
    A 100uF supply bypass capacitor might help.
     
  5. john13busa

    New Member

    Jan 3, 2010
    2
    0
    Why not seperate the two circuits and isolate the power. No additional space just seperate them electronically. they may have created the sound by switching the power through a multivibrator. You could even isolate one of your batteries for a dedicated circuit to the eyes.
     
  6. big hank

    Thread Starter New Member

    Aug 17, 2009
    3
    0
    Would this be just a typical 100uF Cap? By power do you mean Voltage, I may be a able to reconfigure the psu to accomodate 6 volts, but I don't think I'd be able to increase the current by twofold with that deal. Which circuit would I want to bypass? The eyes or the PCB gizmo?

    Thank you for the suggestion!



    I have done that with other projects, I just honestly don't have the real estate for another psu. I think I need to snap a few pics, so you all can see where I'm at, I'm not at the workshop at the moment, I'll be in town on Friday, will try all the suggestions and update with pics!


    I really appreciate the advice guys!:D
     
  7. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Power is voltage times current. Your tiny battery voltage drops when it is overloaded by trying to supply too much current. When the voltage drops then the blue LEDs turn off.

    A 100uF capacitor across the "4.5V" battery on the pcb might be able to hold the voltage high enough to light the blue LEDs when the sound circuit is pulsing.

    Measure the 4.5V while the sound and blue LEDs are both turned on and you will see its voltage drop too low.
    Is the battery a brand new name-brand?
     
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