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I have a 5V supply to turn my circuit on, and i need a one pulse circuit. The condition should be look like this;

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When the circuit energized with 5 V it should go low after t1 time and it should stay low for t2 time. Then it should be switched to high condition and stay like that. This cycle should go like this for one time when circuit energized. How could I achieve that condition for my circuit? Unfortunenatly I can't use any MCU for that.

Note: I'll control a 5 V relay with this circuit if it will make a difference.

Note2: I made a circuit with 555 timer in monostable mode but it needs a switch for the trigger pin. I can't use that because circuit must be automatically do that after energized.

I hope I explained my problem well. Thank you for your possible answers.

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    \$\begingroup\$ Why can't you use an MCU? \$\endgroup\$
    – Finbarr
    Aug 21, 2023 at 8:56
  • \$\begingroup\$ What if the 5 volts comes up slowly (as will happen with most power supplies)? What is the threshold at which the added circuit should begin to start its timer? You need to state T1 and T2 and allow a tolerance band. \$\endgroup\$
    – Andy aka
    Aug 21, 2023 at 8:58
  • \$\begingroup\$ Is it a power supply supervisor? Like CAT803 OR TPS3808? \$\endgroup\$ Aug 21, 2023 at 9:07
  • \$\begingroup\$ @Finbarr It's a requirement for this project. And i'm curious if it can be achieved with a analog circuit. \$\endgroup\$ Aug 21, 2023 at 9:13
  • \$\begingroup\$ @Andyaka T1 and T2 can be 2 or 3 seconds and the power supply rise time is not a problem with that range of time. And any voltage above 2.5V can be considered as threshold voltage. \$\endgroup\$ Aug 21, 2023 at 9:18

1 Answer 1

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What about adding to your monostable Cct a resistor from vcc to the reset pin 4 with a cap between 4 and gnd? The cap at 0v initially will hold off the 555 until the cap is near vcc. I haven't tried but it seems it should work and is simple. If you need it to redisable another larger resistor from pin 4 to gnd to discharge the cap when supply is turned off.

Edit This was asked for pretty much as you're asking in this same group Try this How do I reset NE555 output to LOW when powered on? Should give you an answer or idea to work with

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