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multiple circuits- one power source problem

Discussion in 'General Electronics Discussion' started by vwguy16, Sep 30, 2011.

  1. vwguy16

    vwguy16

    4
    0
    Sep 30, 2011
    Hi,
    I recently started to get into electronics with help of a PC program that allows you to design and test circtuits.

    The circuits that I made are to simulate running lights on a model starship:

    the primary LED flasher circuit that uses a 555 timer to flash 10 LEDs on and off every couple of seconds

    A secondary flasher(555 also) that briefly flashes 4 LEDs on for half a second every 3 seconds

    a fade in circuit..ie when power is applied the leds will take several seconds to fade up to full brightness.

    The idea was to put all 3 circuits inside my model and run the wires down the stand to a single switch and a 9v power supply.

    I had great success making these circuits and when i actually built them using real components they worked as well as the program said they would...individually....

    However, I wanted them to all run off of a single 9v power supply. Problem is if I connect the + wires for the two flashers together and the - wires together and apply power something goes wrong...the primary flasher does not behave the same..in that the flasher seems to be faster and the primary LEDs will turn off when the secondary LEDs turn off...so im guessing something is interfering....

    do i need to isolate the separate circuits somehow ? if so how do i do this?

    Any help would be great !!

    Thanks,
    Andy
     
  2. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    The circuits may make the power supply voltage jump up & down if the power source is inadeqate. Try replacing with a better one or add a capacitor at the junction.
     
  3. vwguy16

    vwguy16

    4
    0
    Sep 30, 2011
    the power supply should be ok as its a fairly high current rating....im running everything in parallel so voltage shouldnt be an issue should it ? (im still learning :) )

    would the size of the capacitor matter ? ..i think i understand what you are suggesting...the capacitor would act to even out the voltage and keep it constant ?

    please put me right if thats not the case...im keen to learn as much as i can
     
  4. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    If you have no decoupling capacitors on the individual circuits then they could cause interference and also be susceptible to interference from the other circuits.
    Long thin wires introduces a resistance in series with the power supply that allows current variations to set up voltage variations.
    Capacitors evens out those current (& voltage) variations.
     
  5. vwguy16

    vwguy16

    4
    0
    Sep 30, 2011
    Ahh I see. Thanks so much for your help ... I shall give this a go tonight.
     
  6. vwguy16

    vwguy16

    4
    0
    Sep 30, 2011
    After reading up on decoupling 555 timers I saw what i needed to do...basically use a .1uF decoupling capacitor on pin 5 and all is well....

    many thanks for your help Requeline!
     
  7. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    Thanks for reporting back, and glad to know you got it figured out!
    Decoupling is often/ easily overlooked, but it's as important as having good dampers on cars and a smooth pavement without potholes on the roads.
     
  8. daddles

    daddles

    443
    3
    Jun 10, 2011
    Too bad we can't solder capacitors between the ears and other protruding body parts of politicians to decouple them too.
     
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