Electronic – Generating a delayed pulse with one 555 timer upon powering up the circuit

555

This is a very beginner's question – I apologize if this is some trivial extension of a known practice.

Can I use one 555 timer without any extra transistors/IC to generate a delayed pulse as shown below upon powering up the circuit?

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The intended circuit has no buttons or other external triggers. It is activated by being suddenly connected to power (from z-wave smartswitch) and is supposed to:

  • after power up, keep output pin low for ~15 seconds
  • put output pin to high for ~5 seconds
  • finally, put it to low and keep it there forever

This probably can be done easier with two 555 timers but I think that one 555 timer should be able to do it as well. This is also a great learning experience in understanding the mechanics of 555.

Best Answer

I created the following circuit that seems to be able to accomplish that task with just one 555 and no external triggers.

Explanation of my circuit:

  • The left-side attempts to simulate a delayed trigger pulse.
    • R1-C1 is slowly decreasing the voltage from high to low and manipulates the length of time when output will be on LOW (~15 seconds)
    • R3-C3 is increasing the voltage but slightly slower than R1-C1 so that Trigger voltage dips below 3V but not for long
  • The right-side is a monostable 555 implementation
    • R4-C4 manipulates the length of time when the output would be on HIGH (~5 seconds)

schematic

simulate this circuit – Schematic created using CircuitLab

Here are the voltage measurements:

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Here are the current measurements:

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I think this implementation works but is there an easier way to accomplish that?