Astable multivibrator mode is the most commonly use mode of the 555 timer. Astable means that the output keeps turning on and off indefinitely. This can also be referred to as going high and low, zeros and ones, etc.

Video below: 555 timer astable multivibrator circuit step by step build and explained with diagram by electronzap Click here to watch directly on YouTube!

555 timer astable multivivrator oscillator circuit diagram by electronzap electronzapdotcom
555 timer astable multivivrator oscillator circuit diagram by electronzap electronzapdotcom

The speed that the 555 time output oscillates on/off, and the percent of time that the output is on versus off (duty cycle), is determined by how fast a capacitor charges to 2/3Vcc and then discharges to 1/3Vcc. These are the 2 conditions where the 555 timer output changes whether it is high or low and whether the capacitor starts charging or discharging.

Video above: Liumy LM2001 multimeter oscilloscope used in a how to format to take oscilloscope measurements of the output of a 555 timer circuit wired up in astable mode.

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