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Here is a functional NE555 push-on push-off switch. But the problem with this is whenever the power source is connected, it starts in random On or Off position.

How to modify it so that it always remains in OFF position when power is just connected (aka. system is restarted).

For actual values, you can see a YouTube video.

Fritzing drawing available

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Reset to default
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Pull up the reset to VCC with a resistor, and place a capacitor between the reset and ground, as show in the schematics.

When you power on the 555, C1 will hold the /RESET line for a brief time. This will reset the flip-flop of the 555.

NOTE: The reset input current on the TTL version of the 555 is very high (between 0.4 mA and 1.5 mA) so R must be rather small. 100 Ohm will ensure that the levels are within specifications.

Adjust the \$R_1 \cdot C_1\$ time constant so that the low-level pulse is longer than your power supply turn-on time.

EDIT: The diode allows quick discharging the capacitor in case there is a very quick turn off/on cycle (thanks @Brian Drummond).

schematic

simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ And if you switch it off and back on, charge stored on C1 holds RESETn high. If that's a problem, a normally reverse biassed diode from C1 to V+ discharges C1 when the power fails. \$\endgroup\$
    – user16324
    Commented Oct 2, 2017 at 10:37
  • \$\begingroup\$ yes, you're correct, I will edit the schematics, thank you \$\endgroup\$
    – next-hack
    Commented Oct 2, 2017 at 10:41
  • \$\begingroup\$ It may not be a problem ... I am just one of those very useful idiots when it comes to testing, lol! But the trick is worth knowing. \$\endgroup\$
    – user16324
    Commented Oct 2, 2017 at 10:43
  • \$\begingroup\$ Yes, in fact the time constant is very fast (assuming a "0"-Ohm load), but I also like stressing my circuits by quickly turn on/off and see if any erratic behaviors occur. The diode will help in preventing them (provided that the circuit will have an equivalent load resistance much smaller than 100 Ohm, otherwise adding the diode might not bring significant advantages). \$\endgroup\$
    – next-hack
    Commented Oct 2, 2017 at 10:48
  • \$\begingroup\$ Yes, without the diode, it seems it turns on "again" when pressing the button, as if it is not obeying the push event for turn-off. \$\endgroup\$
    – Bimal Poudel
    Commented Oct 3, 2017 at 0:08

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