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555 in Bistable Mode - Flip Flop
Left button sends a LOW pulse to trigger pin
Right button sends a LOW pulse to reset pin
Both the trigger (pin 2) and the reset (pin 4) inputs are connected to Vcc through a 10 kΩ resistor. When the set switch is depressed, pin 2 is shorted to ground. This causes the voltage to bypass pin 2, resulting in a momentary low pulse, which triggers the 555. When triggered, the output pin goes high.
In astable or monostable mode, the output pin would remain high until the voltage at the threshold pin (pin 6) reaches two-thirds of the supply voltage. However, because pin 6 isn’t connected to anything in this circuit, no volt-age is ever present on pin 6. Thus, the threshold is never reached, and so the output remains high indefinitely until the 555 is reset by a low pulse on the reset pin (pin 4).
The reset input (pin 4) is connected to Vcc in the same manner as the trigger input. As a result, when the reset switch is pressed, pin 4 is short-circuited to ground, creating a low pulse, which resets the 555 and brings the output back to high.
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