Three little 555 circuits on one AC/DC adaptor? help

Discussion in 'The Projects Forum' started by ALAS, Sep 25, 2013.

  1. ALAS

    Thread Starter New Member

    Sep 25, 2013
    Hi guys,

    I have a problem which seems like it shouldn't be too hard to figure out, but when I searched on the internet for advice, no one else on the internet seems to be doing quite the same thing.

    I made 3 of this simple 555 timer-based circuit, each of which controls a few LEDs: Each of them works great on its own when connected to its own 9V battery. Since they are all going to be inside the same object, I thought it would make the most sense to use an AC adapter to power all of them simultaneously. I am pretty sure I could do it easily using 3 jacks and a guitar-pedal-powering daisy chain setup, but I want to just have one jack.

    At first this seemed like a no-brainer. The adapter I was using is a 9V adapter with 1 amp of current (I do not know the current draw of each of the circuits, but I know that 3 circuits that run well with 250 mA each should run OK on 1 amp). What I did was make "rails" from the + and ground of the jack and then put each of the circuits along them parallel to each other, connecting each to the appropriate rails using the same wires that had connected it to the + and - of the battery originally.

    When connected to the adapter with this jack, the LEDs in the circuits all light up and flash, but they do so erratically. It sort of seems like they are modulating each other - as in, the rate I set each circuit to flash at using the pot in the circuit affects the rate at which the others flash, and the flashes of each speed up and slow down unpredictably.

    What did I do wrong? What is the right way to do this? Is there any way to do this with the adapter I am already using, and just 1 jack?

  2. MrChips


    Oct 2, 2009
    I have said this once before and I will say it again. 555 timer circuits will modulate each other (your words) when powered on the same circuit.

    Replace your 555 chips with CMOS versions, TLC555, LMC555.

    Add decoupling capacitors across the power rails, 0.1μF in parallel with 10μF electrolytic capacitor. For 555 timer circuits, you can put an additional 100μF electrolytic capacitor across the power source.
  3. ALAS

    Thread Starter New Member

    Sep 25, 2013
    thanks for the advice about the CMOS chips. Other than helping the circuits to work independently, will switching to the CMOS 555's otherwise change the function of the circuit?

    if I can't get the other chips in time for when I need to use it, could I just add those capacitors you mentioned and at least have some improvement in the situation?

    Thanks again.
  4. #12


    Nov 30, 2010
    1) No.
    2) Yes.
  5. Brownout

    Well-Known Member

    Jan 10, 2012
    Better make sure the CMOS version has enough output current to drive your loads.