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I trying to create a circuit with only one 555 to send HIGH on output(3) for very short time, like 200ms, then set LOW for something like 20~30 seconds.

Then I'm just need turn on circuit, then: a) fast HIGH (~200ms) b) long LOW (~20-30s)

I already able to make a "default" 555 circuit with stable HIGH/LOW in same timing (1000ms/1000ms), but I'm getting trouble to make this with different HIGH and LOW timmings.

Thanks.

Carlos
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1 Answers1

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General approach is to separate the discharge resistor into two using diodes.

schematic

simulate this circuit – Schematic created using CircuitLab

The capacitor C2 charges through R1 + R3 and discharges through R2, ignoring diode drops and discharge transistor collector voltage when on.

Approximately, on time is proportional to R1 + R3 and off time is proportional to R2, so you can make the ratio suit your application.

Spehro Pefhany
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  • +1, there is an example of the same thing with adjustable mark to space ration in this question. https://electronics.stackexchange.com/questions/336785/ne555-based-speed-controller-circuit-contradicting-pins-in-2-tutorials/336790#336790 – Trevor_G Nov 20 '17 at 03:59
  • Worked great at simulator. Going to build it now, thanks. http://everycircuit.com/circuit/5064547242344448/555-long-delay – Carlos Nov 20 '17 at 15:04
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    Both worked, from @Spehro and "555 timer in astable mode: How can I achieve longer low output than high?" http://everycircuit.com/circuit/5750062543273984 – Carlos Nov 20 '17 at 17:28