First of all I am getting back into electronics after a LONG pause and am going back to the 555 roots. I am attempting to create a simple circuit that will light an LED after a period of time. In the circuit I have a reset, that I would like to...reset the operation.

The problem is, my current circuit is doing the exact opposite of what I want. I feel that I am so close to an answer as it works perfectly....just the direct opposite result I am looking for :) Any help would be greatly appreciated.

I am looking for simplicity so if something is part of the circuit that can be simplified, I am all ears!

Link to tinkercad design: https://www.tinkercad.com/things/2vyzH4CGXoF-problem555-monostable

Tinkercad design

Intended logic: LED remains off for a period of X seconds/minutes. After time elapses, LED will turn on. User can press the switch to reset the LED again for time period.

  • 4
    \$\begingroup\$ wouldn't connecting the LED to supply instead of ground (and if necessary, changing its series resistor) solve your problem? Also, honestly, draw schematics, not wiring diagrams: I'd have to think a lot to understand your board, but with an actual schematic, it would be clear in one blink of an eye :) \$\endgroup\$ May 27, 2021 at 13:57
  • \$\begingroup\$ Would be glad to help you if you provide a schematic rather than the mock-up circuit. There is a schematic editor available with the edit option for your question. Help others help you. \$\endgroup\$ May 27, 2021 at 14:27

1 Answer 1


The 555 timer can source current as well as sink current. You currently have it wired to source current.

While the output is high after being triggered, the 555 is supplying current to your LED. You could wire it so that the anode of your LED is connected to the supply rail and the cathode connected to the 555 output. You will of course still need a series resistor. This way, while the output is low, your LED will light, then once triggered and the output goes high, your LED will extinguish until the time period has expired.

The 555 I just looked up was able to supply 200mA and sink 50ma, so it is able to cope with sinking the current required for an LED.

The website I took this image from has a tutorial about this -

enter image description here


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