Bi-Stable Mode(Flip-Flop):

In bistable mode, both the output states are stable. At each interrupt, the output changes from low (0) to high (1) and vice versa, and stays there. For example, if we have a high (1) output, it will go low(0) once it receives an interrupt and stays low (0) till the next interrupt changes the status. Now we will demonstrate the bistable mode of the 555 timer with an LED and push buttons connected to the trigger pin and reset pin. Pressing the trigger button once will make the LED turn on and stay on. Pressing the reset button will make the LED turn off and stay off.

555 IC in BiStable Mode

555 Timer IC Circuit in Bi-Stable Mode

Pressing the trigger button allows current to flow from Vcc to ground, which causes the voltage at the trigger pin to drop. As we saw in the mono stable mode article, when the trigger pin is at a low voltage, the output gets switched on and the LED lights up. The output stays on until the voltage at the threshold pin goes above 2/3 Vcc. Since the threshold pin is wired to ground in this circuit, it never reaches 2/3 Vcc, so the output stays on indefinitely. Now if the reset button is pressed, the voltage at the reset pin flows to ground and the pin goes low. When the reset pin goes low, the output is switched off.

Applications of Bistable multivibrator:

  • As frequency dividers
  • As a storage device in computer memories or counters
  • As Latches and Counter.
  • Used in digital communications
  • It is also used for reversing to the
  • Supply to a given circuit at regular intervals

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