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Can you please help understanding how this circuit is flashing the two LEDs? I know about transistors, capacitors, and resistors functionality, but can't get how this works without a 555 timer.

enter image description here

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    \$\begingroup\$ asks google about: astable multivibrator \$\endgroup\$
    – Mike
    yesterday
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    \$\begingroup\$ Does this answer your question? Astable multivibrator using transistor \$\endgroup\$
    – awjlogan
    yesterday
  • \$\begingroup\$ Did you read the Wikipedia article? \$\endgroup\$
    – ocrdu
    yesterday
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    \$\begingroup\$ Pretty much every circuit I've ever designed works well without having a 555 timer fitted. Yours is no exception. \$\endgroup\$
    – Andy aka
    yesterday
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The capacitors will alternate between being charged and discharged, thereby turning on and off the transistors making the LEDs blink alternately. This is a passive circuit, no need for a NE555.

More information on: https://www.build-electronic-circuits.com/astable-multivibrator/

It is called an astable multivibrator circuit.

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    \$\begingroup\$ It isn't a passive circuit. Transistors are usually counted as active devices. The circuit is built of discrete components (no IC,) but it is not passive. \$\endgroup\$
    – JRE
    yesterday
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The 555 timer is an integrated circuit intended to make it easier to build oscillators and timed pulses.

Your circuit is an astable multivibrator made with discrete transistors.

The 555 is an integrated circuit containing a bucket of transistors in a very small volume:

enter image description here

Image from the linked Wikipedia article.

The 555 makes it possible to do things that a simple oscillator can't, but it is still built of transistors (and other components.)

ICs aren't magic boxes with little demons inside kicking electrons around.

They are complex electronic circuits with a known and defined structure and function. Some of them could be duplicated with individual parts - you can buy discrete 555 kits with standard components that you can assemble into a functional (though large) 555. Others are so complex (microprocessors, for example) that the equivalent circuit made of standard components would be too large to be practical (or even work.)

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