I have a problem in Falstad that when making a 555 IC based signal delayer that should delay a power-off of a certain device, that the whole circuit behaves really weird and doesn't work as stated by multiple people who tried it out on the internet. Why doesn't it work in the sim?

There is no delay, it turns on as soon as the switch is toggled. When applying putting there a diode it seems to behave very strangely.

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here is a link to captured screen video of the behavior I am facing: https://youtu.be/XtibAHLGqTE

Here is a link to the schematic I was coming out of (but there are many like it): https://elonics.org/adjustable-auto-on-off-delay-timer-circuit-using-555/

  • 3
    \$\begingroup\$ "Really weird" is totally undiagnosable. Explain exactly what the difference(s) between what you expect, and what you see. Edit your question to add this. \$\endgroup\$
    – LordTeddy
    Apr 26, 2023 at 19:25
  • 1
    \$\begingroup\$ If you need a 1 minute timer with some level of accuracy, there are both better and cheaper ways than 555 + 470 uF. \$\endgroup\$
    – winny
    Apr 26, 2023 at 19:35
  • \$\begingroup\$ when you press and then release the switch does it not take 1 minute before the output turns off again? \$\endgroup\$ Apr 26, 2023 at 20:23

1 Answer 1


The simulation is actually wrong. But likely the component values are not entirely well thought anyway. For an ideal 470 uF capacitor it will work, but for a real-world 470uF electrolytic capacitor with leakage current, the value is just unrealistic for real world purposes.

On a real chip, if trigger is active, i.e. low, then threshold voltage is irrelevant, and the output is always high, and disharge pin will be always off. It means that trigger pin overrides the discharge pin.

The point is, don't keep trigger pin low. Pulling trigger low will trigger the delay, start charging the capacitor and set output high, but trigger must be released before capacitor threshold voltage is reached.

It would not work in real life either, if you keep trigger low permanently. And it would likely be affected by non-idealities of real world electrolytic capacitors too, likely requiring much longer time than calculated.


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