555 issue

Discussion in 'The Projects Forum' started by trekpilot, Nov 11, 2013.

  1. trekpilot

    Thread Starter New Member

    Nov 11, 2013

    New here. I have pretty much zero knowledge of electronics. I recently soldered this circuit for my ship lighting. It worked fine on my 9v battery, so I assumed it was ok. I then hacked up a DC power supply and plugged it in. The timing is now uneven and even has a weird double-flicker at the end. Happens on both circuits. I tried with multiple LEDs (with correct resistors) and also on a pre-resistored LED light strip. I also tried different power supply (12v). The flicker changes its pattern but it's still there. Any ideas on what the issue might be?
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    Your DC power supply isnt smoothed enough, so the ripple on the supply is causing the 555 timers to self trigger, put bigger electrolytic capacitors on the supply like 2200uf and 100nf, the timing is also effected by the supply voltage fluctuations, at 9v the timer oscillates between 3v-6v, at 12v it oscillates between 4V to 8V, so you need to use a good regulated supply.
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    That circuit was published by a lawyer; what do you expect? Another crap circuit published on the Internet.

    He forgot power a supply bypass capacitor between Vdd (Pin 8) and Vss (Pin 1).
    He left out the required bypass caps between Pin 5 and Vss (Pin 1).
    He put a series diode in the Vss leg of his circuit.

    Any of which could cause erratic timing and interaction between the timing circuits.

    He didn't specify what the supply voltage is (12V battery?)

    Maybe you could sue him, or hire me as a plaintif's expert witness ;)
  4. trekpilot

    Thread Starter New Member

    Nov 11, 2013
    This seems to have worked!!! I put a 2200uf capacitor between the power supply and the 555 circuits and the flicker is gone! You're a champ. So first problem is solved. In the off position, the current seems to dissipate a bit slower now (assuming because of the capacitor), but I can live with that.

    Now, second issue I just noticed is that the faster of the two flashers seems to have an irregularity every second flash. It's maybe 2 tenths of a second faster than the first. It alternates like that. I just noticed this, and it happens both with the DC power and the battery. Any way to fix that? I'm willing to scrap and try again (I've already put 60+ hours into this model, so a bit of soldering isn't a big deal). Keep in mind please I'm totally clueless. Thanks!

    Edit: The dissipation issue seems to have gone away on its own. Not sure why. The irregularity is still there.
    Last edited: Nov 11, 2013
  5. trekpilot

    Thread Starter New Member

    Nov 11, 2013
    LOL. Interesting that it even works at all with the omissions you mentioned. It seems to be ok, but I'm a perfectionist and the discrepancy in timing I mentioned above is bothering me. I'm open to ideas on how to tackle this. I can follow a diagram and know how to burn myself with a soldering iron, but that's about it.