I just got my 556 timers and I wired it up just like the 555 but now: it flashes one HighTime and stays off then...

I used this calculator and basic diagram: http://www.ohmslawcalculator.com/555-astable-calculator

And changed it to fit the 556: 556 Schematic

You guys have any idea why this is not working?

(P.S.: I used green wires here if lines are overlapping)

Thank you!

  • \$\begingroup\$ I didn't look too close to your circuit, but I think, the 556 doesn't work at 3V. Which kind of 556 do you have? \$\endgroup\$ Commented Jan 2, 2019 at 8:33
  • \$\begingroup\$ Oh; yes; I added it to 5V (WeMos D1Mini) - just did it wrong when I created the schematics for here \$\endgroup\$
    – dessi
    Commented Jan 2, 2019 at 8:34
  • \$\begingroup\$ Does the LED flash on at startup then go off? That 10k resistor is way too high to drive that LED. It may be that you get a spike go through it when you first start it up, then it'll turn off as 10k is much too high. Also is your capacitor really 1 millifarad? That's quite high too! Try scoping the OUT pin (if it really is a 1mF cap you are using, a DMM will do too as it'll be slow enough to see the transition) and see if the output is going from high to low \$\endgroup\$
    – MCG
    Commented Jan 2, 2019 at 8:37
  • \$\begingroup\$ I would have written an answer, but want to clarify these few things first, as it could well be something completely different \$\endgroup\$
    – MCG
    Commented Jan 2, 2019 at 8:38
  • \$\begingroup\$ The LED works with the 10k resistor, when I use the 555; and with the 1mF (1000uf) I want to push the cycle length to ~20 seconds; or you have an alternative for this? And yes: it flashes up on startup; does one cycle but then it stays off. But I will try it with a lower resistor value later. \$\endgroup\$
    – dessi
    Commented Jan 2, 2019 at 9:23


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